--- /dev/null
+/** @file lmdb.h
+ * @brief Lightning memory-mapped database library
+ *
+ * @mainpage Lightning Memory-Mapped Database Manager (LMDB)
+ *
+ * @section intro_sec Introduction
+ * LMDB 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, LMDB 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. LMDB 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
+ * #mdb_reader_check function or the \ref mdb_stat_1 "mdb_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 MDB_USE_SYSV_SEM or
+ * MDB_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 MDB_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 #MDB_NOLOCK flag described under #mdb_env_open().
+ *
+ * - An LMDB 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 #MDB_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 #MDB_NOMEMINIT flag. Applications handling sensitive data
+ * which must not be written should not use this flag. This flag is
+ * irrelevant when using #MDB_WRITEMAP.
+ *
+ * - A thread can only use one transaction at a time, plus any child
+ * transactions. Each transaction belongs to one thread. See below.
+ * The #MDB_NOTLS flag changes this for read-only transactions.
+ *
+ * - Use an MDB_env* in the process which opened it, not after fork().
+ *
+ * - Do not have open an LMDB 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 LMDB 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 2011-2021 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 _LMDB_H_
+#define _LMDB_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 mdb_mode_t;
+#else
+typedef mode_t mdb_mode_t;
+#endif
+
+#ifdef _WIN32
+# define MDB_FMT_Z "I"
+#else
+# define MDB_FMT_Z "z" /**< printf/scanf format modifier for size_t */
+#endif
+
+#ifndef MDB_VL32
+/** Unsigned type used for mapsize, entry counts and page/transaction IDs.
+ *
+ * It is normally size_t, hence the name. Defining MDB_VL32 makes it
+ * uint64_t, but do not try this unless you know what you are doing.
+ */
+typedef size_t mdb_size_t;
+# define MDB_SIZE_MAX SIZE_MAX /**< max #mdb_size_t */
+/** #mdb_size_t printf formats, \b t = one of [diouxX] without quotes */
+# define MDB_PRIy(t) MDB_FMT_Z #t
+/** #mdb_size_t scanf formats, \b t = one of [dioux] without quotes */
+# define MDB_SCNy(t) MDB_FMT_Z #t
+#else
+typedef uint64_t mdb_size_t;
+# define MDB_SIZE_MAX UINT64_MAX
+# define MDB_PRIy(t) PRI##t##64
+# define MDB_SCNy(t) SCN##t##64
+# define mdb_env_create mdb_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 *mdb_filehandle_t;
+#else
+typedef int mdb_filehandle_t;
+#endif
+
+/** @defgroup mdb LMDB API
+ * @{
+ * @brief OpenLDAP Lightning Memory-Mapped Database Manager
+ */
+/** @defgroup Version Version Macros
+ * @{
+ */
+/** Library major version */
+#define MDB_VERSION_MAJOR 0
+/** Library minor version */
+#define MDB_VERSION_MINOR 9
+/** Library patch version */
+#define MDB_VERSION_PATCH 70
+
+/** Combine args a,b,c into a single integer for easy version comparisons */
+#define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
+
+/** The full library version as a single integer */
+#define MDB_VERSION_FULL \
+ MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
+
+/** The release date of this library version */
+#define MDB_VERSION_DATE "December 19, 2015"
+
+/** A stringifier for the version info */
+#define MDB_VERSTR(a,b,c,d) "LMDB " #a "." #b "." #c ": (" d ")"
+
+/** A helper for the stringifier macro */
+#define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
+
+/** The full library version as a C string */
+#define MDB_VERSION_STRING \
+ MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_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 MDB_env MDB_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 MDB_txn MDB_txn;
+
+/** @brief A handle for an individual database in the DB environment. */
+typedef unsigned int MDB_dbi;
+
+/** @brief Opaque structure for navigating through a database */
+typedef struct MDB_cursor MDB_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 #mdb_env_get_maxkeysize() inclusive.
+ * The same applies to data sizes in databases with the #MDB_DUPSORT flag.
+ * Other data items can in theory be from 0 to 0xffffffff bytes long.
+ */
+typedef struct MDB_val {
+ size_t mv_size; /**< size of the data item */
+ void *mv_data; /**< address of the data item */
+} MDB_val;
+
+/** @brief A callback function used to compare two keys in a database */
+typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_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 #mdb_set_relctx().
+ * @todo This feature is currently unimplemented.
+ */
+typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
+
+/** @defgroup mdb_env Environment Flags
+ * @{
+ */
+ /** mmap at a fixed address (experimental) */
+#define MDB_FIXEDMAP 0x01
+ /** no environment directory */
+#define MDB_NOSUBDIR 0x4000
+ /** don't fsync after commit */
+#define MDB_NOSYNC 0x10000
+ /** read only */
+#define MDB_RDONLY 0x20000
+ /** don't fsync metapage after commit */
+#define MDB_NOMETASYNC 0x40000
+ /** use writable mmap */
+#define MDB_WRITEMAP 0x80000
+ /** use asynchronous msync when #MDB_WRITEMAP is used */
+#define MDB_MAPASYNC 0x100000
+ /** tie reader locktable slots to #MDB_txn objects instead of to threads */
+#define MDB_NOTLS 0x200000
+ /** don't do any locking, caller must manage their own locks */
+#define MDB_NOLOCK 0x400000
+ /** don't do readahead (no effect on Windows) */
+#define MDB_NORDAHEAD 0x800000
+ /** don't initialize malloc'd memory before writing to datafile */
+#define MDB_NOMEMINIT 0x1000000
+ /** use the previous snapshot rather than the latest one */
+#define MDB_PREVSNAPSHOT 0x2000000
+/** @} */
+
+/** @defgroup mdb_dbi_open Database Flags
+ * @{
+ */
+ /** use reverse string keys */
+#define MDB_REVERSEKEY 0x02
+ /** use sorted duplicates */
+#define MDB_DUPSORT 0x04
+ /** numeric keys in native byte order, either unsigned int or #mdb_size_t.
+ * (lmdb expects 32-bit int <= size_t <= 32/64-bit mdb_size_t.)
+ * The keys must all be of the same size. */
+#define MDB_INTEGERKEY 0x08
+ /** with #MDB_DUPSORT, sorted dup items have fixed size */
+#define MDB_DUPFIXED 0x10
+ /** with #MDB_DUPSORT, dups are #MDB_INTEGERKEY-style integers */
+#define MDB_INTEGERDUP 0x20
+ /** with #MDB_DUPSORT, use reverse string dups */
+#define MDB_REVERSEDUP 0x40
+ /** create DB if not already existing */
+#define MDB_CREATE 0x40000
+/** @} */
+
+/** @defgroup mdb_put Write Flags
+ * @{
+ */
+/** For put: Don't write if the key already exists. */
+#define MDB_NOOVERWRITE 0x10
+/** Only for #MDB_DUPSORT<br>
+ * For put: don't write if the key and data pair already exist.<br>
+ * For mdb_cursor_del: remove all duplicate data items.
+ */
+#define MDB_NODUPDATA 0x20
+/** For mdb_cursor_put: overwrite the current key/data pair */
+#define MDB_CURRENT 0x40
+/** For put: Just reserve space for data, don't copy it. Return a
+ * pointer to the reserved space.
+ */
+#define MDB_RESERVE 0x10000
+/** Data is being appended, don't split full pages. */
+#define MDB_APPEND 0x20000
+/** Duplicate data is being appended, don't split full pages. */
+#define MDB_APPENDDUP 0x40000
+/** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
+#define MDB_MULTIPLE 0x80000
+/* @} */
+
+/** @defgroup mdb_copy Copy Flags
+ * @{
+ */
+/** Compacting copy: Omit free space from copy, and renumber all
+ * pages sequentially.
+ */
+#define MDB_CP_COMPACT 0x01
+/* @} */
+
+/** @brief Cursor Get operations.
+ *
+ * This is the set of all operations for retrieving data
+ * using a cursor.
+ */
+typedef enum MDB_cursor_op {
+ MDB_FIRST, /**< Position at first key/data item */
+ MDB_FIRST_DUP, /**< Position at first data item of current key.
+ Only for #MDB_DUPSORT */
+ MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
+ MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
+ MDB_GET_CURRENT, /**< Return key/data at current cursor position */
+ MDB_GET_MULTIPLE, /**< Return up to a page of duplicate data items
+ from current cursor position. Move cursor to prepare
+ for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */
+ MDB_LAST, /**< Position at last key/data item */
+ MDB_LAST_DUP, /**< Position at last data item of current key.
+ Only for #MDB_DUPSORT */
+ MDB_NEXT, /**< Position at next data item */
+ MDB_NEXT_DUP, /**< Position at next data item of current key.
+ Only for #MDB_DUPSORT */
+ MDB_NEXT_MULTIPLE, /**< Return up to a page of duplicate data items
+ from next cursor position. Move cursor to prepare
+ for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */
+ MDB_NEXT_NODUP, /**< Position at first data item of next key */
+ MDB_PREV, /**< Position at previous data item */
+ MDB_PREV_DUP, /**< Position at previous data item of current key.
+ Only for #MDB_DUPSORT */
+ MDB_PREV_NODUP, /**< Position at last data item of previous key */
+ MDB_SET, /**< Position at specified key */
+ MDB_SET_KEY, /**< Position at specified key, return key + data */
+ MDB_SET_RANGE, /**< Position at first key greater than or equal to specified key. */
+ MDB_PREV_MULTIPLE /**< Position at previous page and return up to
+ a page of duplicate data items. Only for #MDB_DUPFIXED */
+} MDB_cursor_op;
+
+/** @defgroup errors Return Codes
+ *
+ * BerkeleyDB uses -30800 to -30999, we'll go under them
+ * @{
+ */
+ /** Successful result */
+#define MDB_SUCCESS 0
+ /** key/data pair already exists */
+#define MDB_KEYEXIST (-30799)
+ /** key/data pair not found (EOF) */
+#define MDB_NOTFOUND (-30798)
+ /** Requested page not found - this usually indicates corruption */
+#define MDB_PAGE_NOTFOUND (-30797)
+ /** Located page was wrong type */
+#define MDB_CORRUPTED (-30796)
+ /** Update of meta page failed or environment had fatal error */
+#define MDB_PANIC (-30795)
+ /** Environment version mismatch */
+#define MDB_VERSION_MISMATCH (-30794)
+ /** File is not a valid LMDB file */
+#define MDB_INVALID (-30793)
+ /** Environment mapsize reached */
+#define MDB_MAP_FULL (-30792)
+ /** Environment maxdbs reached */
+#define MDB_DBS_FULL (-30791)
+ /** Environment maxreaders reached */
+#define MDB_READERS_FULL (-30790)
+ /** Too many TLS keys in use - Windows only */
+#define MDB_TLS_FULL (-30789)
+ /** Txn has too many dirty pages */
+#define MDB_TXN_FULL (-30788)
+ /** Cursor stack too deep - internal error */
+#define MDB_CURSOR_FULL (-30787)
+ /** Page has not enough space - internal error */
+#define MDB_PAGE_FULL (-30786)
+ /** Database contents grew beyond environment mapsize */
+#define MDB_MAP_RESIZED (-30785)
+ /** Operation and DB incompatible, or DB type changed. This can mean:
+ * <ul>
+ * <li>The operation expects an #MDB_DUPSORT / #MDB_DUPFIXED database.
+ * <li>Opening a named DB when the unnamed DB has #MDB_DUPSORT / #MDB_INTEGERKEY.
+ * <li>Accessing a data record as a database, or vice versa.
+ * <li>The database was dropped and recreated with different flags.
+ * </ul>
+ */
+#define MDB_INCOMPATIBLE (-30784)
+ /** Invalid reuse of reader locktable slot */
+#define MDB_BAD_RSLOT (-30783)
+ /** Transaction must abort, has a child, or is invalid */
+#define MDB_BAD_TXN (-30782)
+ /** Unsupported size of key/DB name/data, or wrong DUPFIXED size */
+#define MDB_BAD_VALSIZE (-30781)
+ /** The specified DBI was changed unexpectedly */
+#define MDB_BAD_DBI (-30780)
+ /** Unexpected problem - txn should abort */
+#define MDB_PROBLEM (-30779)
+ /** The last defined error code */
+#define MDB_LAST_ERRCODE MDB_PROBLEM
+/** @} */
+
+/** @brief Statistics for a database in the environment */
+typedef struct MDB_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 */
+ mdb_size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
+ mdb_size_t ms_leaf_pages; /**< Number of leaf pages */
+ mdb_size_t ms_overflow_pages; /**< Number of overflow pages */
+ mdb_size_t ms_entries; /**< Number of data items */
+} MDB_stat;
+
+/** @brief Information about the environment */
+typedef struct MDB_envinfo {
+ void *me_mapaddr; /**< Address of map, if fixed */
+ mdb_size_t me_mapsize; /**< Size of the data memory map */
+ mdb_size_t me_last_pgno; /**< ID of the last used page */
+ mdb_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 */
+} MDB_envinfo;
+
+ /** @brief Return the LMDB 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 *mdb_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 LMDB library error is
+ * returned. See @ref errors for a list of LMDB-specific error codes.
+ * @param[in] err The error code
+ * @retval "error message" The description of the error
+ */
+char *mdb_strerror(int err);
+
+ /** @brief Create an LMDB environment handle.
+ *
+ * This function allocates memory for a #MDB_env structure. To release
+ * the allocated memory and discard the handle, call #mdb_env_close().
+ * Before the handle may be used, it must be opened using #mdb_env_open().
+ * Various other options may also need to be set before opening the handle,
+ * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_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 mdb_env_create(MDB_env **env);
+
+ /** @brief Open an environment handle.
+ *
+ * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
+ * @param[in] env An environment handle returned by #mdb_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 mdb_env_set_flags() are also used.
+ * <ul>
+ * <li>#MDB_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>#MDB_NOSUBDIR
+ * By default, LMDB 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>#MDB_RDONLY
+ * Open the environment in read-only mode. No write operations will be
+ * allowed. LMDB will still modify the lock file - except on read-only
+ * filesystems, where LMDB does not use locks.
+ * <li>#MDB_WRITEMAP
+ * Use a writeable memory map unless MDB_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 MDB_WRITEMAP on the same
+ * environment. This can defeat durability (#mdb_env_sync etc).
+ * <li>#MDB_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-MDB_RDONLY commit or #mdb_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 #mdb_env_set_flags().
+ * <li>#MDB_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 #mdb_env_sync() is called. However, if the
+ * filesystem preserves write order and the #MDB_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 (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
+ * hint for when to write transactions to disk, unless #mdb_env_sync()
+ * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
+ * This flag may be changed at any time using #mdb_env_set_flags().
+ * <li>#MDB_MAPASYNC
+ * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
+ * As with #MDB_NOSYNC, a system crash can then corrupt the
+ * database or lose the last transactions. Calling #mdb_env_sync()
+ * ensures on-disk database integrity until next commit.
+ * This flag may be changed at any time using #mdb_env_set_flags().
+ * <li>#MDB_NOTLS
+ * Don't use Thread-Local Storage. Tie reader locktable slots to
+ * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
+ * the slot reserved for the #MDB_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 LMDB's write locking is unaware of the user threads.
+ * <li>#MDB_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>#MDB_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>#MDB_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 #MDB_WRITEMAP,
+ * which writes directly to the mmap instead of using malloc for pages. The
+ * initialization is also skipped if #MDB_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 #mdb_env_set_flags().
+ * <li>#MDB_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>#MDB_VERSION_MISMATCH - the version of the LMDB library doesn't match the
+ * version that created the database environment.
+ * <li>#MDB_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 mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
+
+ /** @brief Copy an LMDB 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 #mdb_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 mdb_env_copy(MDB_env *env, const char *path);
+
+ /** @brief Copy an LMDB 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 #mdb_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 mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd);
+
+ /** @brief Copy an LMDB 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 #mdb_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>#MDB_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 mdb_env_copy2(MDB_env *env, const char *path, unsigned int flags);
+
+ /** @brief Copy an LMDB 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
+ * #mdb_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 #mdb_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 #mdb_env_copy2() for options.
+ * @return A non-zero error value on failure and 0 on success.
+ */
+int mdb_env_copyfd2(MDB_env *env, mdb_filehandle_t fd, unsigned int flags);
+
+ /** @brief Return statistics about the LMDB environment.
+ *
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @param[out] stat The address of an #MDB_stat structure
+ * where the statistics will be copied
+ */
+int mdb_env_stat(MDB_env *env, MDB_stat *stat);
+
+ /** @brief Return information about the LMDB environment.
+ *
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @param[out] stat The address of an #MDB_envinfo structure
+ * where the information will be copied
+ */
+int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
+
+ /** @brief Flush the data buffers to disk.
+ *
+ * Data is always written to disk when #mdb_txn_commit() is called,
+ * but the operating system may keep it buffered. LMDB always flushes
+ * the OS buffers upon commit as well, unless the environment was
+ * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC. This call is
+ * not valid if the environment was opened with #MDB_RDONLY.
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @param[in] force If non-zero, force a synchronous flush. Otherwise
+ * if the environment has the #MDB_NOSYNC flag set the flushes
+ * will be omitted, and with #MDB_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 mdb_env_sync(MDB_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 #mdb_env_create()
+ */
+void mdb_env_close(MDB_env *env);
+
+ /** @brief Set environment flags.
+ *
+ * This may be used to set some flags in addition to those from
+ * #mdb_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 #mdb_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 mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
+
+ /** @brief Get environment flags.
+ *
+ * @param[in] env An environment handle returned by #mdb_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 mdb_env_get_flags(MDB_env *env, unsigned int *flags);
+
+ /** @brief Return the path that was used in #mdb_env_open().
+ *
+ * @param[in] env An environment handle returned by #mdb_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 mdb_env_get_path(MDB_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 LMDB file descriptors have FD_CLOEXEC.
+ * (Until LMDB 0.9.18, only the lockfile had that.)
+ *
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @param[out] fd Address of a mdb_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 mdb_env_get_fd(MDB_env *env, mdb_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 #mdb_env_create() and before #mdb_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, #mdb_txn_begin() will
+ * return #MDB_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 #mdb_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 mdb_env_set_mapsize(MDB_env *env, mdb_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
+ * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
+ * MDB_txn object until it or the #MDB_env object is destroyed.
+ * This function may only be called after #mdb_env_create() and before #mdb_env_open().
+ * @param[in] env An environment handle returned by #mdb_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 mdb_env_set_maxreaders(MDB_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 #mdb_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 mdb_env_get_maxreaders(MDB_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 #mdb_env_create() and before #mdb_env_open().
+ *
+ * Currently a moderate number of slots are cheap but a huge number gets
+ * expensive: 7-120 words per transaction, and every #mdb_dbi_open()
+ * does a linear search of the opened slots.
+ * @param[in] env An environment handle returned by #mdb_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 mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
+
+ /** @brief Get the maximum size of keys and #MDB_DUPSORT data we can write.
+ *
+ * Depends on the compile-time constant #MDB_MAXKEYSIZE. Default 511.
+ * See @ref MDB_val.
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @return The maximum size of a key we can write
+ */
+int mdb_env_get_maxkeysize(MDB_env *env);
+
+ /** @brief Set application information associated with the #MDB_env.
+ *
+ * @param[in] env An environment handle returned by #mdb_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 mdb_env_set_userctx(MDB_env *env, void *ctx);
+
+ /** @brief Get the application information associated with the #MDB_env.
+ *
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @return The pointer set by #mdb_env_set_userctx().
+ */
+void *mdb_env_get_userctx(MDB_env *env);
+
+ /** @brief A callback function for most LMDB assert() failures,
+ * called before printing the message and aborting.
+ *
+ * @param[in] env An environment handle returned by #mdb_env_create().
+ * @param[in] msg The assertion message, not including newline.
+ */
+typedef void MDB_assert_func(MDB_env *env, const char *msg);
+
+ /** Set or reset the assert() callback of the environment.
+ * Disabled if liblmdb is built with NDEBUG.
+ * @note This hack should become obsolete as lmdb's error handling matures.
+ * @param[in] env An environment handle returned by #mdb_env_create().
+ * @param[in] func An #MDB_assert_func function, or 0.
+ * @return A non-zero error value on failure and 0 on success.
+ */
+int mdb_env_set_assert(MDB_env *env, MDB_assert_func *func);
+
+ /** @brief Create a transaction for use with the environment.
+ *
+ * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_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 #MDB_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 #mdb_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
+ * mdb_txn_commit and mdb_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>#MDB_RDONLY
+ * This transaction will not perform any write operations.
+ * <li>#MDB_NOSYNC
+ * Don't flush system buffers to disk when committing this transaction.
+ * <li>#MDB_NOMETASYNC
+ * Flush system buffers but omit metadata flush when committing this transaction.
+ * </ul>
+ * @param[out] txn Address where the new #MDB_txn handle will be stored
+ * @return A non-zero error value on failure and 0 on success. Some possible
+ * errors are:
+ * <ul>
+ * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
+ * must be shut down.
+ * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
+ * mapsize and this environment's map must be resized as well.
+ * See #mdb_env_set_mapsize().
+ * <li>#MDB_READERS_FULL - a read-only transaction was requested and
+ * the reader lock table is full. See #mdb_env_set_maxreaders().
+ * <li>ENOMEM - out of memory.
+ * </ul>
+ */
+int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
+
+ /** @brief Returns the transaction's #MDB_env
+ *
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ */
+MDB_env *mdb_txn_env(MDB_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 #mdb_txn_begin()
+ * @return A transaction ID, valid if input is an active transaction.
+ */
+mdb_size_t mdb_txn_id(MDB_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 #mdb_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 #mdb_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 mdb_txn_commit(MDB_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 #mdb_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 #mdb_txn_begin()
+ */
+void mdb_txn_abort(MDB_txn *txn);
+
+ /** @brief Reset a read-only transaction.
+ *
+ * Abort the transaction like #mdb_txn_abort(), but keep the transaction
+ * handle. #mdb_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 #MDB_NOTLS is in use. The reader table
+ * lock is released, but the table slot stays tied to its thread or
+ * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
+ * its lock table slot if MDB_NOTLS is in use.
+ * Cursors opened within the transaction must not be used
+ * again after this call, except with #mdb_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 #mdb_txn_begin()
+ */
+void mdb_txn_reset(MDB_txn *txn);
+
+ /** @brief Renew a read-only transaction.
+ *
+ * This acquires a new reader lock for a transaction handle that had been
+ * released by #mdb_txn_reset(). It must be called before a reset transaction
+ * may be used again.
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ * @return A non-zero error value on failure and 0 on success. Some possible
+ * errors are:
+ * <ul>
+ * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
+ * must be shut down.
+ * <li>EINVAL - an invalid parameter was specified.
+ * </ul>
+ */
+int mdb_txn_renew(MDB_txn *txn);
+
+/** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
+#define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
+/** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
+#define mdb_close(env,dbi) mdb_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 #mdb_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), #mdb_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 #mdb_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>#MDB_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>#MDB_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>#MDB_INTEGERKEY
+ * Keys are binary integers in native byte order, either unsigned int
+ * or #mdb_size_t, and will be sorted as such.
+ * (lmdb expects 32-bit int <= size_t <= 32/64-bit mdb_size_t.)
+ * The keys must all be of the same size.
+ * <li>#MDB_DUPFIXED
+ * This flag may only be used in combination with #MDB_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 #MDB_GET_MULTIPLE, #MDB_NEXT_MULTIPLE
+ * and #MDB_PREV_MULTIPLE cursor operations may be used to retrieve multiple
+ * items at once.
+ * <li>#MDB_INTEGERDUP
+ * This option specifies that duplicate data items are binary integers,
+ * similar to #MDB_INTEGERKEY keys.
+ * <li>#MDB_REVERSEDUP
+ * This option specifies that duplicate data items should be compared as
+ * strings in reverse order.
+ * <li>#MDB_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 #MDB_dbi handle will be stored
+ * @return A non-zero error value on failure and 0 on success. Some possible
+ * errors are:
+ * <ul>
+ * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
+ * and #MDB_CREATE was not specified.
+ * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
+ * </ul>
+ */
+int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
+
+ /** @brief Retrieve statistics for a database.
+ *
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_dbi_open()
+ * @param[out] stat The address of an #MDB_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 mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
+
+ /** @brief Retrieve the DB flags for a database handle.
+ *
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_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 mdb_dbi_flags(MDB_txn *txn, MDB_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 MDB_BAD_VALSIZE (since the DB name is gone).
+ *
+ * Closing a database handle is not necessary, but lets #mdb_dbi_open()
+ * reuse the handle value. Usually it's better to set a bigger
+ * #mdb_env_set_maxdbs(), unless that value would be large.
+ *
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @param[in] dbi A database handle returned by #mdb_dbi_open()
+ */
+void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
+
+ /** @brief Empty or delete+close a database.
+ *
+ * See #mdb_dbi_close() for restrictions about closing the DB handle.
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_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 mdb_drop(MDB_txn *txn, MDB_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 #mdb_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 #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_dbi_open()
+ * @param[in] cmp A #MDB_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 mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
+
+ /** @brief Set a custom data comparison function for a #MDB_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 #MDB_DUPSORT
+ * flag.
+ * If no comparison function is specified, and no special key flags were specified
+ * with #mdb_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 #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_dbi_open()
+ * @param[in] cmp A #MDB_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 mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
+
+ /** @brief Set a relocation function for a #MDB_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 #MDB_FIXEDMAP option.
+ * Currently the relocation feature is unimplemented and setting
+ * this function has no effect.
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_dbi_open()
+ * @param[in] rel A #MDB_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 mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
+
+ /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
+ *
+ * See #mdb_set_relfunc and #MDB_rel_func for more details.
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_dbi_open()
+ * @param[in] ctx An arbitrary pointer for whatever the application needs.
+ * It will be passed to the callback function set by #mdb_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 mdb_set_relctx(MDB_txn *txn, MDB_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 (#MDB_DUPSORT) then the
+ * first data item for the key will be returned. Retrieval of other
+ * items requires the use of #mdb_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 #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_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>#MDB_NOTFOUND - the key was not in the database.
+ * <li>EINVAL - an invalid parameter was specified.
+ * </ul>
+ */
+int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_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 (#MDB_DUPSORT).
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_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>#MDB_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 #MDB_DUPSORT. The function will
+ * return #MDB_KEYEXIST if the key/data pair already appears in the
+ * database.
+ * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
+ * does not already appear in the database. The function will return
+ * #MDB_KEYEXIST if the key already appears in the database, even if
+ * the database supports duplicates (#MDB_DUPSORT). The \b data
+ * parameter will be set to point to the existing item.
+ * <li>#MDB_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.
+ * LMDB 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 #MDB_DUPSORT.
+ * <li>#MDB_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 #MDB_KEYEXIST error.
+ * <li>#MDB_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>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
+ * <li>#MDB_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 mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_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
+ * (#MDB_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 #MDB_NOTFOUND if the specified key/data
+ * pair is not in the database.
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_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 mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_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 #mdb_cursor_renew().
+ * It can be discarded with #mdb_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
+ * #mdb_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 #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_dbi_open()
+ * @param[out] cursor Address where the new #MDB_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 mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_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 #mdb_cursor_open()
+ */
+void mdb_cursor_close(MDB_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 #mdb_txn_begin()
+ * @param[in] cursor A cursor handle returned by #mdb_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 mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
+
+ /** @brief Return the cursor's transaction handle.
+ *
+ * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
+ */
+MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
+
+ /** @brief Return the cursor's database handle.
+ *
+ * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
+ */
+MDB_dbi mdb_cursor_dbi(MDB_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 #MDB_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 #mdb_get() for restrictions on using the output values.
+ * @param[in] cursor A cursor handle returned by #mdb_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 #MDB_cursor_op
+ * @return A non-zero error value on failure and 0 on success. Some possible
+ * errors are:
+ * <ul>
+ * <li>#MDB_NOTFOUND - no matching key found.
+ * <li>EINVAL - an invalid parameter was specified.
+ * </ul>
+ */
+int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
+ MDB_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 #mdb_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>#MDB_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 (#MDB_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>#MDB_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 #MDB_DUPSORT. The function will
+ * return #MDB_KEYEXIST if the key/data pair already appears in the
+ * database.
+ * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
+ * does not already appear in the database. The function will return
+ * #MDB_KEYEXIST if the key already appears in the database, even if
+ * the database supports duplicates (#MDB_DUPSORT).
+ * <li>#MDB_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 #MDB_DUPSORT.
+ * <li>#MDB_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 #MDB_KEYEXIST error.
+ * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
+ * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a
+ * single request. This flag may only be specified if the database
+ * was opened with #MDB_DUPFIXED. The \b data argument must be an
+ * array of two MDB_vals. The mv_size of the first MDB_val must be
+ * the size of a single data element. The mv_data of the first MDB_val
+ * must point to the beginning of the array of contiguous data elements.
+ * The mv_size of the second MDB_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 MDB_val is unused.
+ * </ul>
+ * @return A non-zero error value on failure and 0 on success. Some possible
+ * errors are:
+ * <ul>
+ * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
+ * <li>#MDB_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 mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_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 MDB_NEXT
+ * can still be used on it.
+ * Both MDB_NEXT and MDB_GET_CURRENT will return the same record after
+ * this operation.
+ * @param[in] cursor A cursor handle returned by #mdb_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>#MDB_NODUPDATA - delete all of the data items for the current key.
+ * This flag may only be specified if the database was opened with #MDB_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 mdb_cursor_del(MDB_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 #MDB_DUPSORT.
+ * @param[in] cursor A cursor handle returned by #mdb_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 mdb_cursor_count(MDB_cursor *cursor, mdb_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 #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_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 mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_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 #MDB_DUPSORT flag.
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_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 mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_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 (MDB_msg_func)(const char *msg, void *ctx);
+
+ /** @brief Dump the entries in the reader lock table.
+ *
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @param[in] func A #MDB_msg_func function
+ * @param[in] ctx Anything the message function needs
+ * @return < 0 on failure, >= 0 on success.
+ */
+int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
+
+ /** @brief Check for stale entries in the reader lock table.
+ *
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @param[out] dead Number of stale slots that were cleared
+ * @return 0 on success, non-zero on failure.
+ */
+int mdb_reader_check(MDB_env *env, int *dead);
+/** @} */
+
+#ifdef __cplusplus
+}
+#endif
+/** @page tools LMDB Command Line Tools
+ The following describes the command line tools that are available for LMDB.
+ \li \ref mdb_copy_1
+ \li \ref mdb_dump_1
+ \li \ref mdb_load_1
+ \li \ref mdb_stat_1
+*/
+
+#endif /* _LMDB_H_ */
projects / ziglmdb / blobdiff