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 /** @file exdb.h
  *  @brief Lightning memory-mapped database library
  *
  *  @mainpage   Lightning Memory-Mapped Database Manager (EXDB)
  *
  *  @section intro_sec Introduction
  *  EXDB is a Btree-based database management library modeled loosely on the
  *  BerkeleyDB API, but much simplified. The entire database is exposed
  *  in a memory map, and all data fetches return data directly
  *  from the mapped memory, so no malloc's or memcpy's occur during
  *  data fetches. As such, the library is extremely simple because it
  *  requires no page caching layer of its own, and it is extremely high
  *  performance and memory-efficient. It is also fully transactional with
  *  full ACID semantics, and when the memory map is read-only, the
  *  database integrity cannot be corrupted by stray pointer writes from
  *  application code.
  *
  *  The library is fully thread-aware and supports concurrent read/write
  *  access from multiple processes and threads. Data pages use a copy-on-
  *  write strategy so no active data pages are ever overwritten, which
  *  also provides resistance to corruption and eliminates the need of any
  *  special recovery procedures after a system crash. Writes are fully
  *  serialized; only one write transaction may be active at a time, which
  *  guarantees that writers can never deadlock. The database structure is
  *  multi-versioned so readers run with no locks; writers cannot block
  *  readers, and readers don't block writers.
  *
  *  Unlike other well-known database mechanisms which use either write-ahead
  *  transaction logs or append-only data writes, EXDB requires no maintenance
  *  during operation. Both write-ahead loggers and append-only databases
  *  require periodic checkpointing and/or compaction of their log or database
  *  files otherwise they grow without bound. EXDB tracks free pages within
  *  the database and re-uses them for new write operations, so the database
  *  size does not grow without bound in normal use.
  *
  *  The memory map can be used as a read-only or read-write map. It is
  *  read-only by default as this provides total immunity to corruption.
  *  Using read-write mode offers much higher write performance, but adds
  *  the possibility for stray application writes thru pointers to silently
  *  corrupt the database. Of course if your application code is known to
  *  be bug-free (...) then this is not an issue.
  *
  *  If this is your first time using a transactional embedded key/value
  *  store, you may find the \ref starting page to be helpful.
  *
  *  @section caveats_sec Caveats
  *  Troubleshooting the lock file, plus semaphores on BSD systems:
  *
  *  - A broken lockfile can cause sync issues.
  *    Stale reader transactions left behind by an aborted program
  *    cause further writes to grow the database quickly, and
  *    stale locks can block further operation.
  *
  *    Fix: Check for stale readers periodically, using the
  *    #edb_reader_check function or the \ref edb_stat_1 "edb_stat" tool.
  *    Stale writers will be cleared automatically on most systems:
  *    - Windows - automatic
  *    - BSD, systems using SysV semaphores - automatic
  *    - Linux, systems using POSIX mutexes with Robust option - automatic
  *    Otherwise just make all programs using the database close it;
  *    the lockfile is always reset on first open of the environment.
  *
  *  - On BSD systems or others configured with EDB_USE_SYSV_SEM or
  *    EDB_USE_POSIX_SEM,
  *    startup can fail due to semaphores owned by another userid.
  *
  *    Fix: Open and close the database as the user which owns the
  *    semaphores (likely last user) or as root, while no other
  *    process is using the database.
  *
  *  Restrictions/caveats (in addition to those listed for some functions):
  *
  *  - Only the database owner should normally use the database on
  *    BSD systems or when otherwise configured with EDB_USE_POSIX_SEM.
  *    Multiple users can cause startup to fail later, as noted above.
  *
  *  - There is normally no pure read-only mode, since readers need write
  *    access to locks and lock file. Exceptions: On read-only filesystems
  *    or with the #EDB_NOLOCK flag described under #edb_env_open().
  *
  *  - An EXDB configuration will often reserve considerable \b unused
  *    memory address space and maybe file size for future growth.
  *    This does not use actual memory or disk space, but users may need
  *    to understand the difference so they won't be scared off.
  *
  *  - By default, in versions before 0.9.10, unused portions of the data
  *    file might receive garbage data from memory freed by other code.
  *    (This does not happen when using the #EDB_WRITEMAP flag.) As of
  *    0.9.10 the default behavior is to initialize such memory before
  *    writing to the data file. Since there may be a slight performance
  *    cost due to this initialization, applications may disable it using
  *    the #EDB_NOMEMINIT flag. Applications handling sensitive data
  *    which must not be written should not use this flag. This flag is
  *    irrelevant when using #EDB_WRITEMAP.
  *
  *  - A thread can only use one transaction at a time, plus any child
  *    transactions.  Each transaction belongs to one thread.  See below.
  *    The #EDB_NOTLS flag changes this for read-only transactions.
  *
  *  - Use an EDB_env* in the process which opened it, not after fork().
  *
  *  - Do not have open an EXDB database twice in the same process at
  *    the same time.  Not even from a plain open() call - close()ing it
  *    breaks fcntl() advisory locking.  (It is OK to reopen it after
  *    fork() - exec*(), since the lockfile has FD_CLOEXEC set.)
  *
  *  - Avoid long-lived transactions.  Read transactions prevent
  *    reuse of pages freed by newer write transactions, thus the
  *    database can grow quickly.  Write transactions prevent
  *    other write transactions, since writes are serialized.
  *
  *  - Avoid suspending a process with active transactions.  These
  *    would then be "long-lived" as above.  Also read transactions
  *    suspended when writers commit could sometimes see wrong data.
  *
  *  ...when several processes can use a database concurrently:
  *
  *  - Avoid aborting a process with an active transaction.
  *    The transaction becomes "long-lived" as above until a check
  *    for stale readers is performed or the lockfile is reset,
  *    since the process may not remove it from the lockfile.
  *
  *    This does not apply to write transactions if the system clears
  *    stale writers, see above.
  *
  *  - If you do that anyway, do a periodic check for stale readers. Or
  *    close the environment once in a while, so the lockfile can get reset.
  *
  *  - Do not use EXDB databases on remote filesystems, even between
  *    processes on the same host.  This breaks flock() on some OSes,
  *    possibly memory map sync, and certainly sync between programs
  *    on different hosts.
  *
  *  - Opening a database can fail if another process is opening or
  *    closing it at exactly the same time.
  *
  *  @author Howard Chu, Symas Corporation.
  *
  *  @copyright Copyright 2011-2020 Howard Chu, Symas Corp. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted only as authorized by the OpenLDAP
  * Public License.
  *
  * A copy of this license is available in the file LICENSE in the
  * top-level directory of the distribution or, alternatively, at
  * <http://www.OpenLDAP.org/license.html>.
  *
  *  @par Derived From:
  * This code is derived from btree.c written by Martin Hedenfalk.
  *
  * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
  * copyright notice and this permission notice appear in all copies.
  *
  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 #ifndef _EXDB_H_
 #define _EXDB_H_
 
 #include <sys/types.h>
 #include <inttypes.h>
 #include <limits.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 /** Unix permissions for creating files, or dummy definition for Windows */
 #ifdef _MSC_VER
 typedef int edb_mode_t;
 #else
 typedef mode_t  edb_mode_t;
 #endif
 
 #ifdef _WIN32
 # define EDB_FMT_Z  "I"
 #else
 # define EDB_FMT_Z  "z"         /**< printf/scanf format modifier for size_t */
 #endif
 
 #ifndef EDB_VL32
 /** Unsigned type used for mapsize, entry counts and page/transaction IDs.
  *
  *  It is normally size_t, hence the name. Defining EDB_VL32 makes it
  *  uint64_t, but do not try this unless you know what you are doing.
  */
 typedef size_t  edb_size_t;
 # define EDB_SIZE_MAX   SIZE_MAX    /**< max #edb_size_t */
 /** #edb_size_t printf formats, \b t = one of [diouxX] without quotes */
 # define EDB_PRIy(t)    EDB_FMT_Z #t
 /** #edb_size_t scanf formats, \b t = one of [dioux] without quotes */
 # define EDB_SCNy(t)    EDB_FMT_Z #t
 #else
 typedef uint64_t    edb_size_t;
 # define EDB_SIZE_MAX   UINT64_MAX
 # define EDB_PRIy(t)    PRI##t##64
 # define EDB_SCNy(t)    SCN##t##64
 # define edb_env_create edb_env_create_vl32 /**< Prevent mixing with non-VL32 builds */
 #endif
 
 /** An abstraction for a file handle.
  *  On POSIX systems file handles are small integers. On Windows
  *  they're opaque pointers.
  */
 #ifdef _WIN32
 typedef void *edb_filehandle_t;
 #else
 typedef int edb_filehandle_t;
 #endif
 
 /** @defgroup edb EXDB API
  *  @{
  *  @brief OpenLDAP Lightning Memory-Mapped Database Manager
  */
 /** @defgroup Version Version Macros
  *  @{
  */
 /** Library major version */
 #define EDB_VERSION_MAJOR   0
 /** Library minor version */
 #define EDB_VERSION_MINOR   9
 /** Library patch version */
 #define EDB_VERSION_PATCH   70
 
 /** Combine args a,b,c into a single integer for easy version comparisons */
 #define EDB_VERINT(a,b,c)   (((a) << 24) | ((b) << 16) | (c))
 
 /** The full library version as a single integer */
 #define EDB_VERSION_FULL    \
     EDB_VERINT(EDB_VERSION_MAJOR,EDB_VERSION_MINOR,EDB_VERSION_PATCH)
 
 /** The release date of this library version */
 #define EDB_VERSION_DATE    "December 19, 2015"
 
 /** A stringifier for the version info */
 #define EDB_VERSTR(a,b,c,d) "EXDB " #a "." #b "." #c ": (" d ")"
 
 /** A helper for the stringifier macro */
 #define EDB_VERFOO(a,b,c,d) EDB_VERSTR(a,b,c,d)
 
 /** The full library version as a C string */
 #define EDB_VERSION_STRING  \
     EDB_VERFOO(EDB_VERSION_MAJOR,EDB_VERSION_MINOR,EDB_VERSION_PATCH,EDB_VERSION_DATE)
 /** @} */
 
 /** @brief Opaque structure for a database environment.
  *
  * A DB environment supports multiple databases, all residing in the same
  * shared-memory map.
  */
 typedef struct EDB_env EDB_env;
 
 /** @brief Opaque structure for a transaction handle.
  *
  * All database operations require a transaction handle. Transactions may be
  * read-only or read-write.
  */
 typedef struct EDB_txn EDB_txn;
 
 /** @brief A handle for an individual database in the DB environment. */
 typedef unsigned int    EDB_dbi;
 
 /** @brief Opaque structure for navigating through a database */
 typedef struct EDB_cursor EDB_cursor;
 
 /** @brief Generic structure used for passing keys and data in and out
  * of the database.
  *
  * Values returned from the database are valid only until a subsequent
  * update operation, or the end of the transaction. Do not modify or
  * free them, they commonly point into the database itself.
  *
  * Key sizes must be between 1 and #edb_env_get_maxkeysize() inclusive.
  * The same applies to data sizes in databases with the #EDB_DUPSORT flag.
  * Other data items can in theory be from 0 to 0xffffffff bytes long.
  */
 typedef struct EDB_val {
     size_t       mv_size;   /**< size of the data item */
     void        *mv_data;   /**< address of the data item */
 } EDB_val;
 
 /** @brief A callback function used to compare two keys in a database */
 typedef int  (EDB_cmp_func)(const EDB_val *a, const EDB_val *b);
 
 /** @brief A callback function used to relocate a position-dependent data item
  * in a fixed-address database.
  *
  * The \b newptr gives the item's desired address in
  * the memory map, and \b oldptr gives its previous address. The item's actual
  * data resides at the address in \b item.  This callback is expected to walk
  * through the fields of the record in \b item and modify any
  * values based at the \b oldptr address to be relative to the \b newptr address.
  * @param[in,out] item The item that is to be relocated.
  * @param[in] oldptr The previous address.
  * @param[in] newptr The new address to relocate to.
  * @param[in] relctx An application-provided context, set by #edb_set_relctx().
  * @todo This feature is currently unimplemented.
  */
 typedef void (EDB_rel_func)(EDB_val *item, void *oldptr, void *newptr, void *relctx);
 
 /** @defgroup   edb_env Environment Flags
  *  @{
  */
     /** mmap at a fixed address (experimental) */
 #define EDB_FIXEDMAP    0x01
     /** no environment directory */
 #define EDB_NOSUBDIR    0x4000
     /** don't fsync after commit */
 #define EDB_NOSYNC      0x10000
     /** read only */
 #define EDB_RDONLY      0x20000
     /** don't fsync metapage after commit */
 #define EDB_NOMETASYNC      0x40000
     /** use writable mmap */
 #define EDB_WRITEMAP        0x80000
     /** use asynchronous msync when #EDB_WRITEMAP is used */
 #define EDB_MAPASYNC        0x100000
     /** tie reader locktable slots to #EDB_txn objects instead of to threads */
 #define EDB_NOTLS       0x200000
     /** don't do any locking, caller must manage their own locks */
 #define EDB_NOLOCK      0x400000
     /** don't do readahead (no effect on Windows) */
 #define EDB_NORDAHEAD   0x800000
     /** don't initialize malloc'd memory before writing to datafile */
 #define EDB_NOMEMINIT   0x1000000
     /** use the previous snapshot rather than the latest one */
 #define EDB_PREVSNAPSHOT    0x2000000
 /** @} */
 
 /** @defgroup   edb_dbi_open    Database Flags
  *  @{
  */
     /** use reverse string keys */
 #define EDB_REVERSEKEY  0x02
     /** use sorted duplicates */
 #define EDB_DUPSORT     0x04
     /** numeric keys in native byte order, either unsigned int or #edb_size_t.
      *  (exdb expects 32-bit int <= size_t <= 32/64-bit edb_size_t.)
      *  The keys must all be of the same size. */
 #define EDB_INTEGERKEY  0x08
     /** with #EDB_DUPSORT, sorted dup items have fixed size */
 #define EDB_DUPFIXED    0x10
     /** with #EDB_DUPSORT, dups are #EDB_INTEGERKEY-style integers */
 #define EDB_INTEGERDUP  0x20
     /** with #EDB_DUPSORT, use reverse string dups */
 #define EDB_REVERSEDUP  0x40
     /** create DB if not already existing */
 #define EDB_CREATE      0x40000
 /** @} */
 
 /** @defgroup edb_put   Write Flags
  *  @{
  */
 /** For put: Don't write if the key already exists. */
 #define EDB_NOOVERWRITE 0x10
 /** Only for #EDB_DUPSORT<br>
  * For put: don't write if the key and data pair already exist.<br>
  * For edb_cursor_del: remove all duplicate data items.
  */
 #define EDB_NODUPDATA   0x20
 /** For edb_cursor_put: overwrite the current key/data pair */
 #define EDB_CURRENT 0x40
 /** For put: Just reserve space for data, don't copy it. Return a
  * pointer to the reserved space.
  */
 #define EDB_RESERVE 0x10000
 /** Data is being appended, don't split full pages. */
 #define EDB_APPEND  0x20000
 /** Duplicate data is being appended, don't split full pages. */
 #define EDB_APPENDDUP   0x40000
 /** Store multiple data items in one call. Only for #EDB_DUPFIXED. */
 #define EDB_MULTIPLE    0x80000
 /*  @} */
 
 /** @defgroup edb_copy  Copy Flags
  *  @{
  */
 /** Compacting copy: Omit free space from copy, and renumber all
  * pages sequentially.
  */
 #define EDB_CP_COMPACT  0x01
 /*  @} */
 
 /** @brief Cursor Get operations.
  *
  *  This is the set of all operations for retrieving data
  *  using a cursor.
  */
 typedef enum EDB_cursor_op {
     EDB_FIRST,              /**< Position at first key/data item */
     EDB_FIRST_DUP,          /**< Position at first data item of current key.
                                 Only for #EDB_DUPSORT */
     EDB_GET_BOTH,           /**< Position at key/data pair. Only for #EDB_DUPSORT */
     EDB_GET_BOTH_RANGE,     /**< position at key, nearest data. Only for #EDB_DUPSORT */
     EDB_GET_CURRENT,        /**< Return key/data at current cursor position */
     EDB_GET_MULTIPLE,       /**< Return up to a page of duplicate data items
                                 from current cursor position. Move cursor to prepare
                                 for #EDB_NEXT_MULTIPLE. Only for #EDB_DUPFIXED */
     EDB_LAST,               /**< Position at last key/data item */
     EDB_LAST_DUP,           /**< Position at last data item of current key.
                                 Only for #EDB_DUPSORT */
     EDB_NEXT,               /**< Position at next data item */
     EDB_NEXT_DUP,           /**< Position at next data item of current key.
                                 Only for #EDB_DUPSORT */
     EDB_NEXT_MULTIPLE,      /**< Return up to a page of duplicate data items
                                 from next cursor position. Move cursor to prepare
                                 for #EDB_NEXT_MULTIPLE. Only for #EDB_DUPFIXED */
     EDB_NEXT_NODUP,         /**< Position at first data item of next key */
     EDB_PREV,               /**< Position at previous data item */
     EDB_PREV_DUP,           /**< Position at previous data item of current key.
                                 Only for #EDB_DUPSORT */
     EDB_PREV_NODUP,         /**< Position at last data item of previous key */
     EDB_SET,                /**< Position at specified key */
     EDB_SET_KEY,            /**< Position at specified key, return key + data */
     EDB_SET_RANGE,          /**< Position at first key greater than or equal to specified key. */
     EDB_PREV_MULTIPLE       /**< Position at previous page and return up to
                                 a page of duplicate data items. Only for #EDB_DUPFIXED */
 } EDB_cursor_op;
 
 /** @defgroup  errors   Return Codes
  *
  *  BerkeleyDB uses -30800 to -30999, we'll go under them
  *  @{
  */
     /** Successful result */
 #define EDB_SUCCESS  0
     /** key/data pair already exists */
 #define EDB_KEYEXIST    (-30799)
     /** key/data pair not found (EOF) */
 #define EDB_NOTFOUND    (-30798)
     /** Requested page not found - this usually indicates corruption */
 #define EDB_PAGE_NOTFOUND   (-30797)
     /** Located page was wrong type */
 #define EDB_CORRUPTED   (-30796)
     /** Update of meta page failed or environment had fatal error */
 #define EDB_PANIC       (-30795)
     /** Environment version mismatch */
 #define EDB_VERSION_MISMATCH    (-30794)
     /** File is not a valid EXDB file */
 #define EDB_INVALID (-30793)
     /** Environment mapsize reached */
 #define EDB_MAP_FULL    (-30792)
     /** Environment maxdbs reached */
 #define EDB_DBS_FULL    (-30791)
     /** Environment maxreaders reached */
 #define EDB_READERS_FULL    (-30790)
     /** Too many TLS keys in use - Windows only */
 #define EDB_TLS_FULL    (-30789)
     /** Txn has too many dirty pages */
 #define EDB_TXN_FULL    (-30788)
     /** Cursor stack too deep - internal error */
 #define EDB_CURSOR_FULL (-30787)
     /** Page has not enough space - internal error */
 #define EDB_PAGE_FULL   (-30786)
     /** Database contents grew beyond environment mapsize */
 #define EDB_MAP_RESIZED (-30785)
     /** Operation and DB incompatible, or DB type changed. This can mean:
      *  <ul>
      *  <li>The operation expects an #EDB_DUPSORT / #EDB_DUPFIXED database.
      *  <li>Opening a named DB when the unnamed DB has #EDB_DUPSORT / #EDB_INTEGERKEY.
      *  <li>Accessing a data record as a database, or vice versa.
      *  <li>The database was dropped and recreated with different flags.
      *  </ul>
      */
 #define EDB_INCOMPATIBLE    (-30784)
     /** Invalid reuse of reader locktable slot */
 #define EDB_BAD_RSLOT       (-30783)
     /** Transaction must abort, has a child, or is invalid */
 #define EDB_BAD_TXN         (-30782)
     /** Unsupported size of key/DB name/data, or wrong DUPFIXED size */
 #define EDB_BAD_VALSIZE     (-30781)
     /** The specified DBI was changed unexpectedly */
 #define EDB_BAD_DBI     (-30780)
     /** Unexpected problem - txn should abort */
 #define EDB_PROBLEM     (-30779)
     /** The last defined error code */
 #define EDB_LAST_ERRCODE    EDB_PROBLEM
 /** @} */
 
 /** @brief Statistics for a database in the environment */
 typedef struct EDB_stat {
     unsigned int    ms_psize;           /**< Size of a database page.
                                             This is currently the same for all databases. */
     unsigned int    ms_depth;           /**< Depth (height) of the B-tree */
     edb_size_t      ms_branch_pages;    /**< Number of internal (non-leaf) pages */
     edb_size_t      ms_leaf_pages;      /**< Number of leaf pages */
     edb_size_t      ms_overflow_pages;  /**< Number of overflow pages */
     edb_size_t      ms_entries;         /**< Number of data items */
 } EDB_stat;
 
 /** @brief Information about the environment */
 typedef struct EDB_envinfo {
     void    *me_mapaddr;            /**< Address of map, if fixed */
     edb_size_t  me_mapsize;             /**< Size of the data memory map */
     edb_size_t  me_last_pgno;           /**< ID of the last used page */
     edb_size_t  me_last_txnid;          /**< ID of the last committed transaction */
     unsigned int me_maxreaders;     /**< max reader slots in the environment */
     unsigned int me_numreaders;     /**< max reader slots used in the environment */
 } EDB_envinfo;
 
     /** @brief Return the EXDB library version information.
      *
      * @param[out] major if non-NULL, the library major version number is copied here
      * @param[out] minor if non-NULL, the library minor version number is copied here
      * @param[out] patch if non-NULL, the library patch version number is copied here
      * @retval "version string" The library version as a string
      */
 char *edb_version(int *major, int *minor, int *patch);
 
     /** @brief Return a string describing a given error code.
      *
      * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
      * function. If the error code is greater than or equal to 0, then the string
      * returned by the system function strerror(3) is returned. If the error code
      * is less than 0, an error string corresponding to the EXDB library error is
      * returned. See @ref errors for a list of EXDB-specific error codes.
      * @param[in] err The error code
      * @retval "error message" The description of the error
      */
 char *edb_strerror(int err);
 
     /** @brief Create an EXDB environment handle.
      *
      * This function allocates memory for a #EDB_env structure. To release
      * the allocated memory and discard the handle, call #edb_env_close().
      * Before the handle may be used, it must be opened using #edb_env_open().
      * Various other options may also need to be set before opening the handle,
      * e.g. #edb_env_set_mapsize(), #edb_env_set_maxreaders(), #edb_env_set_maxdbs(),
      * depending on usage requirements.
      * @param[out] env The address where the new handle will be stored
      * @return A non-zero error value on failure and 0 on success.
      */
 int  edb_env_create(EDB_env **env);
 
     /** @brief Open an environment handle.
      *
      * If this function fails, #edb_env_close() must be called to discard the #EDB_env handle.
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[in] path The directory in which the database files reside. This
      * directory must already exist and be writable.
      * @param[in] flags Special options for this environment. This parameter
      * must be set to 0 or by bitwise OR'ing together one or more of the
      * values described here.
      * Flags set by edb_env_set_flags() are also used.
      * <ul>
      *  <li>#EDB_FIXEDMAP
      *      use a fixed address for the mmap region. This flag must be specified
      *      when creating the environment, and is stored persistently in the environment.
      *      If successful, the memory map will always reside at the same virtual address
      *      and pointers used to reference data items in the database will be constant
      *      across multiple invocations. This option may not always work, depending on
      *      how the operating system has allocated memory to shared libraries and other uses.
      *      The feature is highly experimental.
      *  <li>#EDB_NOSUBDIR
      *      By default, EXDB creates its environment in a directory whose
      *      pathname is given in \b path, and creates its data and lock files
      *      under that directory. With this option, \b path is used as-is for
      *      the database main data file. The database lock file is the \b path
      *      with "-lock" appended.
      *  <li>#EDB_RDONLY
      *      Open the environment in read-only mode. No write operations will be
      *      allowed. EXDB will still modify the lock file - except on read-only
      *      filesystems, where EXDB does not use locks.
      *  <li>#EDB_WRITEMAP
      *      Use a writeable memory map unless EDB_RDONLY is set. This uses
      *      fewer mallocs but loses protection from application bugs
      *      like wild pointer writes and other bad updates into the database.
      *      This may be slightly faster for DBs that fit entirely in RAM, but
      *      is slower for DBs larger than RAM.
      *      Incompatible with nested transactions.
      *      Do not mix processes with and without EDB_WRITEMAP on the same
      *      environment.  This can defeat durability (#edb_env_sync etc).
      *  <li>#EDB_NOMETASYNC
      *      Flush system buffers to disk only once per transaction, omit the
      *      metadata flush. Defer that until the system flushes files to disk,
      *      or next non-EDB_RDONLY commit or #edb_env_sync(). This optimization
      *      maintains database integrity, but a system crash may undo the last
      *      committed transaction. I.e. it preserves the ACI (atomicity,
      *      consistency, isolation) but not D (durability) database property.
      *      This flag may be changed at any time using #edb_env_set_flags().
      *  <li>#EDB_NOSYNC
      *      Don't flush system buffers to disk when committing a transaction.
      *      This optimization means a system crash can corrupt the database or
      *      lose the last transactions if buffers are not yet flushed to disk.
      *      The risk is governed by how often the system flushes dirty buffers
      *      to disk and how often #edb_env_sync() is called.  However, if the
      *      filesystem preserves write order and the #EDB_WRITEMAP flag is not
      *      used, transactions exhibit ACI (atomicity, consistency, isolation)
      *      properties and only lose D (durability).  I.e. database integrity
      *      is maintained, but a system crash may undo the final transactions.
      *      Note that (#EDB_NOSYNC | #EDB_WRITEMAP) leaves the system with no
      *      hint for when to write transactions to disk, unless #edb_env_sync()
      *      is called. (#EDB_MAPASYNC | #EDB_WRITEMAP) may be preferable.
      *      This flag may be changed at any time using #edb_env_set_flags().
      *  <li>#EDB_MAPASYNC
      *      When using #EDB_WRITEMAP, use asynchronous flushes to disk.
      *      As with #EDB_NOSYNC, a system crash can then corrupt the
      *      database or lose the last transactions. Calling #edb_env_sync()
      *      ensures on-disk database integrity until next commit.
      *      This flag may be changed at any time using #edb_env_set_flags().
      *  <li>#EDB_NOTLS
      *      Don't use Thread-Local Storage. Tie reader locktable slots to
      *      #EDB_txn objects instead of to threads. I.e. #edb_txn_reset() keeps
      *      the slot reseved for the #EDB_txn object. A thread may use parallel
      *      read-only transactions. A read-only transaction may span threads if
      *      the user synchronizes its use. Applications that multiplex many
      *      user threads over individual OS threads need this option. Such an
      *      application must also serialize the write transactions in an OS
      *      thread, since EXDB's write locking is unaware of the user threads.
      *  <li>#EDB_NOLOCK
      *      Don't do any locking. If concurrent access is anticipated, the
      *      caller must manage all concurrency itself. For proper operation
      *      the caller must enforce single-writer semantics, and must ensure
      *      that no readers are using old transactions while a writer is
      *      active. The simplest approach is to use an exclusive lock so that
      *      no readers may be active at all when a writer begins.
      *  <li>#EDB_NORDAHEAD
      *      Turn off readahead. Most operating systems perform readahead on
      *      read requests by default. This option turns it off if the OS
      *      supports it. Turning it off may help random read performance
      *      when the DB is larger than RAM and system RAM is full.
      *      The option is not implemented on Windows.
      *  <li>#EDB_NOMEMINIT
      *      Don't initialize malloc'd memory before writing to unused spaces
      *      in the data file. By default, memory for pages written to the data
      *      file is obtained using malloc. While these pages may be reused in
      *      subsequent transactions, freshly malloc'd pages will be initialized
      *      to zeroes before use. This avoids persisting leftover data from other
      *      code (that used the heap and subsequently freed the memory) into the
      *      data file. Note that many other system libraries may allocate
      *      and free memory from the heap for arbitrary uses. E.g., stdio may
      *      use the heap for file I/O buffers. This initialization step has a
      *      modest performance cost so some applications may want to disable
      *      it using this flag. This option can be a problem for applications
      *      which handle sensitive data like passwords, and it makes memory
      *      checkers like Valgrind noisy. This flag is not needed with #EDB_WRITEMAP,
      *      which writes directly to the mmap instead of using malloc for pages. The
      *      initialization is also skipped if #EDB_RESERVE is used; the
      *      caller is expected to overwrite all of the memory that was
      *      reserved in that case.
      *      This flag may be changed at any time using #edb_env_set_flags().
      *  <li>#EDB_PREVSNAPSHOT
      *      Open the environment with the previous snapshot rather than the latest
      *      one. This loses the latest transaction, but may help work around some
      *      types of corruption. If opened with write access, this must be the
      *      only process using the environment. This flag is automatically reset
      *      after a write transaction is successfully committed.
      * </ul>
      * @param[in] mode The UNIX permissions to set on created files and semaphores.
      * This parameter is ignored on Windows.
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>#EDB_VERSION_MISMATCH - the version of the EXDB library doesn't match the
      *  version that created the database environment.
      *  <li>#EDB_INVALID - the environment file headers are corrupted.
      *  <li>ENOENT - the directory specified by the path parameter doesn't exist.
      *  <li>EACCES - the user didn't have permission to access the environment files.
      *  <li>EAGAIN - the environment was locked by another process.
      * </ul>
      */
 int  edb_env_open(EDB_env *env, const char *path, unsigned int flags, edb_mode_t mode);
 
     /** @brief Copy an EXDB environment to the specified path.
      *
      * This function may be used to make a backup of an existing environment.
      * No lockfile is created, since it gets recreated at need.
      * @note This call can trigger significant file size growth if run in
      * parallel with write transactions, because it employs a read-only
      * transaction. See long-lived transactions under @ref caveats_sec.
      * @param[in] env An environment handle returned by #edb_env_create(). It
      * must have already been opened successfully.
      * @param[in] path The directory in which the copy will reside. This
      * directory must already exist and be writable but must otherwise be
      * empty.
      * @return A non-zero error value on failure and 0 on success.
      */
 int  edb_env_copy(EDB_env *env, const char *path);
 
     /** @brief Copy an EXDB environment to the specified file descriptor.
      *
      * This function may be used to make a backup of an existing environment.
      * No lockfile is created, since it gets recreated at need.
      * @note This call can trigger significant file size growth if run in
      * parallel with write transactions, because it employs a read-only
      * transaction. See long-lived transactions under @ref caveats_sec.
      * @param[in] env An environment handle returned by #edb_env_create(). It
      * must have already been opened successfully.
      * @param[in] fd The filedescriptor to write the copy to. It must
      * have already been opened for Write access.
      * @return A non-zero error value on failure and 0 on success.
      */
 int  edb_env_copyfd(EDB_env *env, edb_filehandle_t fd);
 
     /** @brief Copy an EXDB environment to the specified path, with options.
      *
      * This function may be used to make a backup of an existing environment.
      * No lockfile is created, since it gets recreated at need.
      * @note This call can trigger significant file size growth if run in
      * parallel with write transactions, because it employs a read-only
      * transaction. See long-lived transactions under @ref caveats_sec.
      * @param[in] env An environment handle returned by #edb_env_create(). It
      * must have already been opened successfully.
      * @param[in] path The directory in which the copy will reside. This
      * directory must already exist and be writable but must otherwise be
      * empty.
      * @param[in] flags Special options for this operation. This parameter
      * must be set to 0 or by bitwise OR'ing together one or more of the
      * values described here.
      * <ul>
      *  <li>#EDB_CP_COMPACT - Perform compaction while copying: omit free
      *      pages and sequentially renumber all pages in output. This option
      *      consumes more CPU and runs more slowly than the default.
      *      Currently it fails if the environment has suffered a page leak.
      * </ul>
      * @return A non-zero error value on failure and 0 on success.
      */
 int  edb_env_copy2(EDB_env *env, const char *path, unsigned int flags);
 
     /** @brief Copy an EXDB environment to the specified file descriptor,
      *  with options.
      *
      * This function may be used to make a backup of an existing environment.
      * No lockfile is created, since it gets recreated at need. See
      * #edb_env_copy2() for further details.
      * @note This call can trigger significant file size growth if run in
      * parallel with write transactions, because it employs a read-only
      * transaction. See long-lived transactions under @ref caveats_sec.
      * @param[in] env An environment handle returned by #edb_env_create(). It
      * must have already been opened successfully.
      * @param[in] fd The filedescriptor to write the copy to. It must
      * have already been opened for Write access.
      * @param[in] flags Special options for this operation.
      * See #edb_env_copy2() for options.
      * @return A non-zero error value on failure and 0 on success.
      */
 int  edb_env_copyfd2(EDB_env *env, edb_filehandle_t fd, unsigned int flags);
 
     /** @brief Return statistics about the EXDB environment.
      *
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[out] stat The address of an #EDB_stat structure
      *  where the statistics will be copied
      */
 int  edb_env_stat(EDB_env *env, EDB_stat *stat);
 
     /** @brief Return information about the EXDB environment.
      *
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[out] stat The address of an #EDB_envinfo structure
      *  where the information will be copied
      */
 int  edb_env_info(EDB_env *env, EDB_envinfo *stat);
 
     /** @brief Flush the data buffers to disk.
      *
      * Data is always written to disk when #edb_txn_commit() is called,
      * but the operating system may keep it buffered. EXDB always flushes
      * the OS buffers upon commit as well, unless the environment was
      * opened with #EDB_NOSYNC or in part #EDB_NOMETASYNC. This call is
      * not valid if the environment was opened with #EDB_RDONLY.
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[in] force If non-zero, force a synchronous flush.  Otherwise
      *  if the environment has the #EDB_NOSYNC flag set the flushes
      *  will be omitted, and with #EDB_MAPASYNC they will be asynchronous.
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EACCES - the environment is read-only.
      *  <li>EINVAL - an invalid parameter was specified.
      *  <li>EIO - an error occurred during synchronization.
      * </ul>
      */
 int  edb_env_sync(EDB_env *env, int force);
 
     /** @brief Close the environment and release the memory map.
      *
      * Only a single thread may call this function. All transactions, databases,
      * and cursors must already be closed before calling this function. Attempts to
      * use any such handles after calling this function will cause a SIGSEGV.
      * The environment handle will be freed and must not be used again after this call.
      * @param[in] env An environment handle returned by #edb_env_create()
      */
 void edb_env_close(EDB_env *env);
 
     /** @brief Set environment flags.
      *
      * This may be used to set some flags in addition to those from
      * #edb_env_open(), or to unset these flags.  If several threads
      * change the flags at the same time, the result is undefined.
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[in] flags The flags to change, bitwise OR'ed together
      * @param[in] onoff A non-zero value sets the flags, zero clears them.
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_env_set_flags(EDB_env *env, unsigned int flags, int onoff);
 
     /** @brief Get environment flags.
      *
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[out] flags The address of an integer to store the flags
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_env_get_flags(EDB_env *env, unsigned int *flags);
 
     /** @brief Return the path that was used in #edb_env_open().
      *
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[out] path Address of a string pointer to contain the path. This
      * is the actual string in the environment, not a copy. It should not be
      * altered in any way.
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_env_get_path(EDB_env *env, const char **path);
 
     /** @brief Return the filedescriptor for the given environment.
      *
      * This function may be called after fork(), so the descriptor can be
      * closed before exec*().  Other EXDB file descriptors have FD_CLOEXEC.
      * (Until EXDB 0.9.18, only the lockfile had that.)
      *
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[out] fd Address of a edb_filehandle_t to contain the descriptor.
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_env_get_fd(EDB_env *env, edb_filehandle_t *fd);
 
     /** @brief Set the size of the memory map to use for this environment.
      *
      * The size should be a multiple of the OS page size. The default is
      * 10485760 bytes. The size of the memory map is also the maximum size
      * of the database. The value should be chosen as large as possible,
      * to accommodate future growth of the database.
      * This function should be called after #edb_env_create() and before #edb_env_open().
      * It may be called at later times if no transactions are active in
      * this process. Note that the library does not check for this condition,
      * the caller must ensure it explicitly.
      *
      * The new size takes effect immediately for the current process but
      * will not be persisted to any others until a write transaction has been
      * committed by the current process. Also, only mapsize increases are
      * persisted into the environment.
      *
      * If the mapsize is increased by another process, and data has grown
      * beyond the range of the current mapsize, #edb_txn_begin() will
      * return #EDB_MAP_RESIZED. This function may be called with a size
      * of zero to adopt the new size.
      *
      * Any attempt to set a size smaller than the space already consumed
      * by the environment will be silently changed to the current size of the used space.
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[in] size The size in bytes
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified, or the environment has
      *      an active write transaction.
      * </ul>
      */
 int  edb_env_set_mapsize(EDB_env *env, edb_size_t size);
 
     /** @brief Set the maximum number of threads/reader slots for the environment.
      *
      * This defines the number of slots in the lock table that is used to track readers in the
      * the environment. The default is 126.
      * Starting a read-only transaction normally ties a lock table slot to the
      * current thread until the environment closes or the thread exits. If
      * EDB_NOTLS is in use, #edb_txn_begin() instead ties the slot to the
      * EDB_txn object until it or the #EDB_env object is destroyed.
      * This function may only be called after #edb_env_create() and before #edb_env_open().
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[in] readers The maximum number of reader lock table slots
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified, or the environment is already open.
      * </ul>
      */
 int  edb_env_set_maxreaders(EDB_env *env, unsigned int readers);
 
     /** @brief Get the maximum number of threads/reader slots for the environment.
      *
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[out] readers Address of an integer to store the number of readers
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_env_get_maxreaders(EDB_env *env, unsigned int *readers);
 
     /** @brief Set the maximum number of named databases for the environment.
      *
      * This function is only needed if multiple databases will be used in the
      * environment. Simpler applications that use the environment as a single
      * unnamed database can ignore this option.
      * This function may only be called after #edb_env_create() and before #edb_env_open().
      *
      * Currently a moderate number of slots are cheap but a huge number gets
      * expensive: 7-120 words per transaction, and every #edb_dbi_open()
      * does a linear search of the opened slots.
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[in] dbs The maximum number of databases
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified, or the environment is already open.
      * </ul>
      */
 int  edb_env_set_maxdbs(EDB_env *env, EDB_dbi dbs);
 
     /** @brief Get the maximum size of keys and #EDB_DUPSORT data we can write.
      *
      * Depends on the compile-time constant #EDB_MAXKEYSIZE. Default 511.
      * See @ref EDB_val.
      * @param[in] env An environment handle returned by #edb_env_create()
      * @return The maximum size of a key we can write
      */
 int  edb_env_get_maxkeysize(EDB_env *env);
 
     /** @brief Set application information associated with the #EDB_env.
      *
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[in] ctx An arbitrary pointer for whatever the application needs.
      * @return A non-zero error value on failure and 0 on success.
      */
 int  edb_env_set_userctx(EDB_env *env, void *ctx);
 
     /** @brief Get the application information associated with the #EDB_env.
      *
      * @param[in] env An environment handle returned by #edb_env_create()
      * @return The pointer set by #edb_env_set_userctx().
      */
 void *edb_env_get_userctx(EDB_env *env);
 
     /** @brief A callback function for most EXDB assert() failures,
      * called before printing the message and aborting.
      *
      * @param[in] env An environment handle returned by #edb_env_create().
      * @param[in] msg The assertion message, not including newline.
      */
 typedef void EDB_assert_func(EDB_env *env, const char *msg);
 
     /** Set or reset the assert() callback of the environment.
      * Disabled if libexdb is buillt with NDEBUG.
      * @note This hack should become obsolete as exdb's error handling matures.
      * @param[in] env An environment handle returned by #edb_env_create().
      * @param[in] func An #EDB_assert_func function, or 0.
      * @return A non-zero error value on failure and 0 on success.
      */
 int  edb_env_set_assert(EDB_env *env, EDB_assert_func *func);
 
     /** @brief Create a transaction for use with the environment.
      *
      * The transaction handle may be discarded using #edb_txn_abort() or #edb_txn_commit().
      * @note A transaction and its cursors must only be used by a single
      * thread, and a thread may only have a single transaction at a time.
      * If #EDB_NOTLS is in use, this does not apply to read-only transactions.
      * @note Cursors may not span transactions.
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[in] parent If this parameter is non-NULL, the new transaction
      * will be a nested transaction, with the transaction indicated by \b parent
      * as its parent. Transactions may be nested to any level. A parent
      * transaction and its cursors may not issue any other operations than
      * edb_txn_commit and edb_txn_abort while it has active child transactions.
      * @param[in] flags Special options for this transaction. This parameter
      * must be set to 0 or by bitwise OR'ing together one or more of the
      * values described here.
      * <ul>
      *  <li>#EDB_RDONLY
      *      This transaction will not perform any write operations.
      *  <li>#EDB_NOSYNC
      *      Don't flush system buffers to disk when committing this transaction.
      *  <li>#EDB_NOMETASYNC
      *      Flush system buffers but omit metadata flush when committing this transaction.
      * </ul>
      * @param[out] txn Address where the new #EDB_txn handle will be stored
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>#EDB_PANIC - a fatal error occurred earlier and the environment
      *      must be shut down.
      *  <li>#EDB_MAP_RESIZED - another process wrote data beyond this EDB_env's
      *      mapsize and this environment's map must be resized as well.
      *      See #edb_env_set_mapsize().
      *  <li>#EDB_READERS_FULL - a read-only transaction was requested and
      *      the reader lock table is full. See #edb_env_set_maxreaders().
      *  <li>ENOMEM - out of memory.
      * </ul>
      */
 int  edb_txn_begin(EDB_env *env, EDB_txn *parent, unsigned int flags, EDB_txn **txn);
 
     /** @brief Returns the transaction's #EDB_env
      *
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      */
 EDB_env *edb_txn_env(EDB_txn *txn);
 
     /** @brief Return the transaction's ID.
      *
      * This returns the identifier associated with this transaction. For a
      * read-only transaction, this corresponds to the snapshot being read;
      * concurrent readers will frequently have the same transaction ID.
      *
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @return A transaction ID, valid if input is an active transaction.
      */
 edb_size_t edb_txn_id(EDB_txn *txn);
 
     /** @brief Commit all the operations of a transaction into the database.
      *
      * The transaction handle is freed. It and its cursors must not be used
      * again after this call, except with #edb_cursor_renew().
      * @note Earlier documentation incorrectly said all cursors would be freed.
      * Only write-transactions free cursors.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      *  <li>ENOSPC - no more disk space.
      *  <li>EIO - a low-level I/O error occurred while writing.
      *  <li>ENOMEM - out of memory.
      * </ul>
      */
 int  edb_txn_commit(EDB_txn *txn);
 
     /** @brief Abandon all the operations of the transaction instead of saving them.
      *
      * The transaction handle is freed. It and its cursors must not be used
      * again after this call, except with #edb_cursor_renew().
      * @note Earlier documentation incorrectly said all cursors would be freed.
      * Only write-transactions free cursors.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      */
 void edb_txn_abort(EDB_txn *txn);
 
     /** @brief Reset a read-only transaction.
      *
      * Abort the transaction like #edb_txn_abort(), but keep the transaction
      * handle. #edb_txn_renew() may reuse the handle. This saves allocation
      * overhead if the process will start a new read-only transaction soon,
      * and also locking overhead if #EDB_NOTLS is in use. The reader table
      * lock is released, but the table slot stays tied to its thread or
      * #EDB_txn. Use edb_txn_abort() to discard a reset handle, and to free
      * its lock table slot if EDB_NOTLS is in use.
      * Cursors opened within the transaction must not be used
      * again after this call, except with #edb_cursor_renew().
      * Reader locks generally don't interfere with writers, but they keep old
      * versions of database pages allocated. Thus they prevent the old pages
      * from being reused when writers commit new data, and so under heavy load
      * the database size may grow much more rapidly than otherwise.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      */
 void edb_txn_reset(EDB_txn *txn);
 
     /** @brief Renew a read-only transaction.
      *
      * This acquires a new reader lock for a transaction handle that had been
      * released by #edb_txn_reset(). It must be called before a reset transaction
      * may be used again.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>#EDB_PANIC - a fatal error occurred earlier and the environment
      *      must be shut down.
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_txn_renew(EDB_txn *txn);
 
 /** Compat with version <= 0.9.4, avoid clash with libedb from EDB Tools project */
 #define edb_open(txn,name,flags,dbi)    edb_dbi_open(txn,name,flags,dbi)
 /** Compat with version <= 0.9.4, avoid clash with libedb from EDB Tools project */
 #define edb_close(env,dbi)              edb_dbi_close(env,dbi)
 
     /** @brief Open a database in the environment.
      *
      * A database handle denotes the name and parameters of a database,
      * independently of whether such a database exists.
      * The database handle may be discarded by calling #edb_dbi_close().
      * The old database handle is returned if the database was already open.
      * The handle may only be closed once.
      *
      * The database handle will be private to the current transaction until
      * the transaction is successfully committed. If the transaction is
      * aborted the handle will be closed automatically.
      * After a successful commit the handle will reside in the shared
      * environment, and may be used by other transactions.
      *
      * This function must not be called from multiple concurrent
      * transactions in the same process. A transaction that uses
      * this function must finish (either commit or abort) before
      * any other transaction in the process may use this function.
      *
      * To use named databases (with name != NULL), #edb_env_set_maxdbs()
      * must be called before opening the environment.  Database names are
      * keys in the unnamed database, and may be read but not written.
      *
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] name The name of the database to open. If only a single
      *  database is needed in the environment, this value may be NULL.
      * @param[in] flags Special options for this database. This parameter
      * must be set to 0 or by bitwise OR'ing together one or more of the
      * values described here.
      * <ul>
      *  <li>#EDB_REVERSEKEY
      *      Keys are strings to be compared in reverse order, from the end
      *      of the strings to the beginning. By default, Keys are treated as strings and
      *      compared from beginning to end.
      *  <li>#EDB_DUPSORT
      *      Duplicate keys may be used in the database. (Or, from another perspective,
      *      keys may have multiple data items, stored in sorted order.) By default
      *      keys must be unique and may have only a single data item.
      *  <li>#EDB_INTEGERKEY
      *      Keys are binary integers in native byte order, either unsigned int
      *      or #edb_size_t, and will be sorted as such.
      *      (exdb expects 32-bit int <= size_t <= 32/64-bit edb_size_t.)
      *      The keys must all be of the same size.
      *  <li>#EDB_DUPFIXED
      *      This flag may only be used in combination with #EDB_DUPSORT. This option
      *      tells the library that the data items for this database are all the same
      *      size, which allows further optimizations in storage and retrieval. When
      *      all data items are the same size, the #EDB_GET_MULTIPLE, #EDB_NEXT_MULTIPLE
      *      and #EDB_PREV_MULTIPLE cursor operations may be used to retrieve multiple
      *      items at once.
      *  <li>#EDB_INTEGERDUP
      *      This option specifies that duplicate data items are binary integers,
      *      similar to #EDB_INTEGERKEY keys.
      *  <li>#EDB_REVERSEDUP
      *      This option specifies that duplicate data items should be compared as
      *      strings in reverse order.
      *  <li>#EDB_CREATE
      *      Create the named database if it doesn't exist. This option is not
      *      allowed in a read-only transaction or a read-only environment.
      * </ul>
      * @param[out] dbi Address where the new #EDB_dbi handle will be stored
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>#EDB_NOTFOUND - the specified database doesn't exist in the environment
      *      and #EDB_CREATE was not specified.
      *  <li>#EDB_DBS_FULL - too many databases have been opened. See #edb_env_set_maxdbs().
      * </ul>
      */
 int  edb_dbi_open(EDB_txn *txn, const char *name, unsigned int flags, EDB_dbi *dbi);
 
     /** @brief Retrieve statistics for a database.
      *
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[out] stat The address of an #EDB_stat structure
      *  where the statistics will be copied
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_stat(EDB_txn *txn, EDB_dbi dbi, EDB_stat *stat);
 
     /** @brief Retrieve the DB flags for a database handle.
      *
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[out] flags Address where the flags will be returned.
      * @return A non-zero error value on failure and 0 on success.
      */
 int edb_dbi_flags(EDB_txn *txn, EDB_dbi dbi, unsigned int *flags);
 
     /** @brief Close a database handle. Normally unnecessary. Use with care:
      *
      * This call is not mutex protected. Handles should only be closed by
      * a single thread, and only if no other threads are going to reference
      * the database handle or one of its cursors any further. Do not close
      * a handle if an existing transaction has modified its database.
      * Doing so can cause misbehavior from database corruption to errors
      * like EDB_BAD_VALSIZE (since the DB name is gone).
      *
      * Closing a database handle is not necessary, but lets #edb_dbi_open()
      * reuse the handle value.  Usually it's better to set a bigger
      * #edb_env_set_maxdbs(), unless that value would be large.
      *
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      */
 void edb_dbi_close(EDB_env *env, EDB_dbi dbi);
 
     /** @brief Empty or delete+close a database.
      *
      * See #edb_dbi_close() for restrictions about closing the DB handle.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[in] del 0 to empty the DB, 1 to delete it from the
      * environment and close the DB handle.
      * @return A non-zero error value on failure and 0 on success.
      */
 int  edb_drop(EDB_txn *txn, EDB_dbi dbi, int del);
 
     /** @brief Set a custom key comparison function for a database.
      *
      * The comparison function is called whenever it is necessary to compare a
      * key specified by the application with a key currently stored in the database.
      * If no comparison function is specified, and no special key flags were specified
      * with #edb_dbi_open(), the keys are compared lexically, with shorter keys collating
      * before longer keys.
      * @warning This function must be called before any data access functions are used,
      * otherwise data corruption may occur. The same comparison function must be used by every
      * program accessing the database, every time the database is used.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[in] cmp A #EDB_cmp_func function
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_set_compare(EDB_txn *txn, EDB_dbi dbi, EDB_cmp_func *cmp);
 
     /** @brief Set a custom data comparison function for a #EDB_DUPSORT database.
      *
      * This comparison function is called whenever it is necessary to compare a data
      * item specified by the application with a data item currently stored in the database.
      * This function only takes effect if the database was opened with the #EDB_DUPSORT
      * flag.
      * If no comparison function is specified, and no special key flags were specified
      * with #edb_dbi_open(), the data items are compared lexically, with shorter items collating
      * before longer items.
      * @warning This function must be called before any data access functions are used,
      * otherwise data corruption may occur. The same comparison function must be used by every
      * program accessing the database, every time the database is used.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[in] cmp A #EDB_cmp_func function
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_set_dupsort(EDB_txn *txn, EDB_dbi dbi, EDB_cmp_func *cmp);
 
     /** @brief Set a relocation function for a #EDB_FIXEDMAP database.
      *
      * @todo The relocation function is called whenever it is necessary to move the data
      * of an item to a different position in the database (e.g. through tree
      * balancing operations, shifts as a result of adds or deletes, etc.). It is
      * intended to allow address/position-dependent data items to be stored in
      * a database in an environment opened with the #EDB_FIXEDMAP option.
      * Currently the relocation feature is unimplemented and setting
      * this function has no effect.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[in] rel A #EDB_rel_func function
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_set_relfunc(EDB_txn *txn, EDB_dbi dbi, EDB_rel_func *rel);
 
     /** @brief Set a context pointer for a #EDB_FIXEDMAP database's relocation function.
      *
      * See #edb_set_relfunc and #EDB_rel_func for more details.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[in] ctx An arbitrary pointer for whatever the application needs.
      * It will be passed to the callback function set by #edb_set_relfunc
      * as its \b relctx parameter whenever the callback is invoked.
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_set_relctx(EDB_txn *txn, EDB_dbi dbi, void *ctx);
 
     /** @brief Get items from a database.
      *
      * This function retrieves key/data pairs from the database. The address
      * and length of the data associated with the specified \b key are returned
      * in the structure to which \b data refers.
      * If the database supports duplicate keys (#EDB_DUPSORT) then the
      * first data item for the key will be returned. Retrieval of other
      * items requires the use of #edb_cursor_get().
      *
      * @note The memory pointed to by the returned values is owned by the
      * database. The caller need not dispose of the memory, and may not
      * modify it in any way. For values returned in a read-only transaction
      * any modification attempts will cause a SIGSEGV.
      * @note Values returned from the database are valid only until a
      * subsequent update operation, or the end of the transaction.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[in] key The key to search for in the database
      * @param[out] data The data corresponding to the key
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>#EDB_NOTFOUND - the key was not in the database.
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_get(EDB_txn *txn, EDB_dbi dbi, EDB_val *key, EDB_val *data);
 
     /** @brief Store items into a database.
      *
      * This function stores key/data pairs in the database. The default behavior
      * is to enter the new key/data pair, replacing any previously existing key
      * if duplicates are disallowed, or adding a duplicate data item if
      * duplicates are allowed (#EDB_DUPSORT).
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[in] key The key to store in the database
      * @param[in,out] data The data to store
      * @param[in] flags Special options for this operation. This parameter
      * must be set to 0 or by bitwise OR'ing together one or more of the
      * values described here.
      * <ul>
      *  <li>#EDB_NODUPDATA - enter the new key/data pair only if it does not
      *      already appear in the database. This flag may only be specified
      *      if the database was opened with #EDB_DUPSORT. The function will
      *      return #EDB_KEYEXIST if the key/data pair already appears in the
      *      database.
      *  <li>#EDB_NOOVERWRITE - enter the new key/data pair only if the key
      *      does not already appear in the database. The function will return
      *      #EDB_KEYEXIST if the key already appears in the database, even if
      *      the database supports duplicates (#EDB_DUPSORT). The \b data
      *      parameter will be set to point to the existing item.
      *  <li>#EDB_RESERVE - reserve space for data of the given size, but
      *      don't copy the given data. Instead, return a pointer to the
      *      reserved space, which the caller can fill in later - before
      *      the next update operation or the transaction ends. This saves
      *      an extra memcpy if the data is being generated later.
      *      EXDB does nothing else with this memory, the caller is expected
      *      to modify all of the space requested. This flag must not be
      *      specified if the database was opened with #EDB_DUPSORT.
      *  <li>#EDB_APPEND - append the given key/data pair to the end of the
      *      database. This option allows fast bulk loading when keys are
      *      already known to be in the correct order. Loading unsorted keys
      *      with this flag will cause a #EDB_KEYEXIST error.
      *  <li>#EDB_APPENDDUP - as above, but for sorted dup data.
      * </ul>
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>#EDB_MAP_FULL - the database is full, see #edb_env_set_mapsize().
      *  <li>#EDB_TXN_FULL - the transaction has too many dirty pages.
      *  <li>EACCES - an attempt was made to write in a read-only transaction.
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_put(EDB_txn *txn, EDB_dbi dbi, EDB_val *key, EDB_val *data,
                 unsigned int flags);
 
     /** @brief Delete items from a database.
      *
      * This function removes key/data pairs from the database.
      * If the database does not support sorted duplicate data items
      * (#EDB_DUPSORT) the data parameter is ignored.
      * If the database supports sorted duplicates and the data parameter
      * is NULL, all of the duplicate data items for the key will be
      * deleted. Otherwise, if the data parameter is non-NULL
      * only the matching data item will be deleted.
      * This function will return #EDB_NOTFOUND if the specified key/data
      * pair is not in the database.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[in] key The key to delete from the database
      * @param[in] data The data to delete
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EACCES - an attempt was made to write in a read-only transaction.
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_del(EDB_txn *txn, EDB_dbi dbi, EDB_val *key, EDB_val *data);
 
     /** @brief Create a cursor handle.
      *
      * A cursor is associated with a specific transaction and database.
      * A cursor cannot be used when its database handle is closed.  Nor
      * when its transaction has ended, except with #edb_cursor_renew().
      * It can be discarded with #edb_cursor_close().
      * A cursor in a write-transaction can be closed before its transaction
      * ends, and will otherwise be closed when its transaction ends.
      * A cursor in a read-only transaction must be closed explicitly, before
      * or after its transaction ends. It can be reused with
      * #edb_cursor_renew() before finally closing it.
      * @note Earlier documentation said that cursors in every transaction
      * were closed when the transaction committed or aborted.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[out] cursor Address where the new #EDB_cursor handle will be stored
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_cursor_open(EDB_txn *txn, EDB_dbi dbi, EDB_cursor **cursor);
 
     /** @brief Close a cursor handle.
      *
      * The cursor handle will be freed and must not be used again after this call.
      * Its transaction must still be live if it is a write-transaction.
      * @param[in] cursor A cursor handle returned by #edb_cursor_open()
      */
 void edb_cursor_close(EDB_cursor *cursor);
 
     /** @brief Renew a cursor handle.
      *
      * A cursor is associated with a specific transaction and database.
      * Cursors that are only used in read-only
      * transactions may be re-used, to avoid unnecessary malloc/free overhead.
      * The cursor may be associated with a new read-only transaction, and
      * referencing the same database handle as it was created with.
      * This may be done whether the previous transaction is live or dead.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] cursor A cursor handle returned by #edb_cursor_open()
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_cursor_renew(EDB_txn *txn, EDB_cursor *cursor);
 
     /** @brief Return the cursor's transaction handle.
      *
      * @param[in] cursor A cursor handle returned by #edb_cursor_open()
      */
 EDB_txn *edb_cursor_txn(EDB_cursor *cursor);
 
     /** @brief Return the cursor's database handle.
      *
      * @param[in] cursor A cursor handle returned by #edb_cursor_open()
      */
 EDB_dbi edb_cursor_dbi(EDB_cursor *cursor);
 
     /** @brief Retrieve by cursor.
      *
      * This function retrieves key/data pairs from the database. The address and length
      * of the key are returned in the object to which \b key refers (except for the
      * case of the #EDB_SET option, in which the \b key object is unchanged), and
      * the address and length of the data are returned in the object to which \b data
      * refers.
      * See #edb_get() for restrictions on using the output values.
      * @param[in] cursor A cursor handle returned by #edb_cursor_open()
      * @param[in,out] key The key for a retrieved item
      * @param[in,out] data The data of a retrieved item
      * @param[in] op A cursor operation #EDB_cursor_op
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>#EDB_NOTFOUND - no matching key found.
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_cursor_get(EDB_cursor *cursor, EDB_val *key, EDB_val *data,
                 EDB_cursor_op op);
 
     /** @brief Store by cursor.
      *
      * This function stores key/data pairs into the database.
      * The cursor is positioned at the new item, or on failure usually near it.
      * @note Earlier documentation incorrectly said errors would leave the
      * state of the cursor unchanged.
      * @param[in] cursor A cursor handle returned by #edb_cursor_open()
      * @param[in] key The key operated on.
      * @param[in] data The data operated on.
      * @param[in] flags Options for this operation. This parameter
      * must be set to 0 or one of the values described here.
      * <ul>
      *  <li>#EDB_CURRENT - replace the item at the current cursor position.
      *      The \b key parameter must still be provided, and must match it.
      *      If using sorted duplicates (#EDB_DUPSORT) the data item must still
      *      sort into the same place. This is intended to be used when the
      *      new data is the same size as the old. Otherwise it will simply
      *      perform a delete of the old record followed by an insert.
      *  <li>#EDB_NODUPDATA - enter the new key/data pair only if it does not
      *      already appear in the database. This flag may only be specified
      *      if the database was opened with #EDB_DUPSORT. The function will
      *      return #EDB_KEYEXIST if the key/data pair already appears in the
      *      database.
      *  <li>#EDB_NOOVERWRITE - enter the new key/data pair only if the key
      *      does not already appear in the database. The function will return
      *      #EDB_KEYEXIST if the key already appears in the database, even if
      *      the database supports duplicates (#EDB_DUPSORT).
      *  <li>#EDB_RESERVE - reserve space for data of the given size, but
      *      don't copy the given data. Instead, return a pointer to the
      *      reserved space, which the caller can fill in later - before
      *      the next update operation or the transaction ends. This saves
      *      an extra memcpy if the data is being generated later. This flag
      *      must not be specified if the database was opened with #EDB_DUPSORT.
      *  <li>#EDB_APPEND - append the given key/data pair to the end of the
      *      database. No key comparisons are performed. This option allows
      *      fast bulk loading when keys are already known to be in the
      *      correct order. Loading unsorted keys with this flag will cause
      *      a #EDB_KEYEXIST error.
      *  <li>#EDB_APPENDDUP - as above, but for sorted dup data.
      *  <li>#EDB_MULTIPLE - store multiple contiguous data elements in a
      *      single request. This flag may only be specified if the database
      *      was opened with #EDB_DUPFIXED. The \b data argument must be an
      *      array of two EDB_vals. The mv_size of the first EDB_val must be
      *      the size of a single data element. The mv_data of the first EDB_val
      *      must point to the beginning of the array of contiguous data elements.
      *      The mv_size of the second EDB_val must be the count of the number
      *      of data elements to store. On return this field will be set to
      *      the count of the number of elements actually written. The mv_data
      *      of the second EDB_val is unused.
      * </ul>
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>#EDB_MAP_FULL - the database is full, see #edb_env_set_mapsize().
      *  <li>#EDB_TXN_FULL - the transaction has too many dirty pages.
      *  <li>EACCES - an attempt was made to write in a read-only transaction.
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_cursor_put(EDB_cursor *cursor, EDB_val *key, EDB_val *data,
                 unsigned int flags);
 
     /** @brief Delete current key/data pair
      *
      * This function deletes the key/data pair to which the cursor refers.
      * This does not invalidate the cursor, so operations such as EDB_NEXT
      * can still be used on it.
      * Both EDB_NEXT and EDB_GET_CURRENT will return the same record after
      * this operation.
      * @param[in] cursor A cursor handle returned by #edb_cursor_open()
      * @param[in] flags Options for this operation. This parameter
      * must be set to 0 or one of the values described here.
      * <ul>
      *  <li>#EDB_NODUPDATA - delete all of the data items for the current key.
      *      This flag may only be specified if the database was opened with #EDB_DUPSORT.
      * </ul>
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EACCES - an attempt was made to write in a read-only transaction.
      *  <li>EINVAL - an invalid parameter was specified.
      * </ul>
      */
 int  edb_cursor_del(EDB_cursor *cursor, unsigned int flags);
 
     /** @brief Return count of duplicates for current key.
      *
      * This call is only valid on databases that support sorted duplicate
      * data items #EDB_DUPSORT.
      * @param[in] cursor A cursor handle returned by #edb_cursor_open()
      * @param[out] countp Address where the count will be stored
      * @return A non-zero error value on failure and 0 on success. Some possible
      * errors are:
      * <ul>
      *  <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
      * </ul>
      */
 int  edb_cursor_count(EDB_cursor *cursor, edb_size_t *countp);
 
     /** @brief Compare two data items according to a particular database.
      *
      * This returns a comparison as if the two data items were keys in the
      * specified database.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[in] a The first item to compare
      * @param[in] b The second item to compare
      * @return < 0 if a < b, 0 if a == b, > 0 if a > b
      */
 int  edb_cmp(EDB_txn *txn, EDB_dbi dbi, const EDB_val *a, const EDB_val *b);
 
     /** @brief Compare two data items according to a particular database.
      *
      * This returns a comparison as if the two items were data items of
      * the specified database. The database must have the #EDB_DUPSORT flag.
      * @param[in] txn A transaction handle returned by #edb_txn_begin()
      * @param[in] dbi A database handle returned by #edb_dbi_open()
      * @param[in] a The first item to compare
      * @param[in] b The second item to compare
      * @return < 0 if a < b, 0 if a == b, > 0 if a > b
      */
 int  edb_dcmp(EDB_txn *txn, EDB_dbi dbi, const EDB_val *a, const EDB_val *b);
 
     /** @brief A callback function used to print a message from the library.
      *
      * @param[in] msg The string to be printed.
      * @param[in] ctx An arbitrary context pointer for the callback.
      * @return < 0 on failure, >= 0 on success.
      */
 typedef int (EDB_msg_func)(const char *msg, void *ctx);
 
     /** @brief Dump the entries in the reader lock table.
      *
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[in] func A #EDB_msg_func function
      * @param[in] ctx Anything the message function needs
      * @return < 0 on failure, >= 0 on success.
      */
 int edb_reader_list(EDB_env *env, EDB_msg_func *func, void *ctx);
 
     /** @brief Check for stale entries in the reader lock table.
      *
      * @param[in] env An environment handle returned by #edb_env_create()
      * @param[out] dead Number of stale slots that were cleared
      * @return 0 on success, non-zero on failure.
      */
 int edb_reader_check(EDB_env *env, int *dead);
 /** @} */
 
 #ifdef __cplusplus
 }
 #endif
 /** @page tools EXDB Command Line Tools
     The following describes the command line tools that are available for EXDB.
     \li \ref edb_copy_1
     \li \ref edb_dump_1
     \li \ref edb_load_1
     \li \ref edb_stat_1
 */
 
 #endif /* _EXDB_H_ */

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