/** @file mdb.h * @brief memory-mapped database library * * @mainpage MDB Memory-Mapped Database Manager * MDB is a Btree-based database management library modeled loosely on the * BerkeleyDB API, but much simplified. The entire database is exposed * in a read-only 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 because 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, MDB 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. MDB 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. * * @author Howard Chu, Symas Corporation. * * @copyright Copyright 2011 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 * . * * @par Derived From: * This code is derived from btree.c written by Martin Hedenfalk. * * Copyright (c) 2009, 2010 Martin Hedenfalk * * 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 _MDB_H_ #define _MDB_H_ #include /** @defgroup public Public API * @{ */ /** @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 0 /** 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 "September 1, 2011" /** A stringifier for the version info */ #define MDB_VERSTR(a,b,c,d) "MDB " #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) /** @} */ /** 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; /** 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; /** A handle for an individual database in the DB environment. */ typedef unsigned int MDB_dbi; /** Opaque structure for navigating through a database */ typedef struct MDB_cursor MDB_cursor; /** Generic structure used for passing keys and data in and out of the database. */ typedef struct MDB_val { size_t mv_size; /**< size of the data item */ void *mv_data; /**< address of the data item */ } MDB_val; /** A callback function used to compare two keys in a database */ typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b); /** 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 */ #define MDB_FIXEDMAP 0x01 /** don't fsync after commit */ #define MDB_NOSYNC 0x10000 /** read only */ #define MDB_RDONLY 0x20000 /** @} */ /** @defgroup mdb_open Database Flags * @{ */ /** use reverse string keys */ #define MDB_REVERSEKEY 0x02 /** use sorted duplicates */ #define MDB_DUPSORT 0x04 /** numeric keys in native byte order. * 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 numeric in native byte order */ #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
* For put: don't write if the key and data pair already exist.
* 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 /* @} */ /** 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_MULTIPLE, /**< Return all the duplicate data items at the current cursor position. 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 all duplicate data items at the next cursor position. Only for #MDB_DUPFIXED */ MDB_NEXT_NODUP, /**< Position at first data item of next key. Only for #MDB_DUPSORT */ 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. Only for #MDB_DUPSORT */ MDB_SET, /**< Position at specified key */ MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */ } 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, probably I/O error */ #define MDB_PANIC (-30795) /** Environment version mismatch */ #define MDB_VERSION_MISMATCH (-30794) /** @} */ /** 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 */ size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */ size_t ms_leaf_pages; /**< Number of leaf pages */ size_t ms_overflow_pages; /**< Number of overflow pages */ size_t ms_entries; /**< Number of data items */ } MDB_stat; /** Return the mdb 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); /** 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 MDB library error is * returned. See @ref errors for a list of MDB-specific error codes. * @param[in] err The error code * @retval "error message" The description of the error */ char *mdb_strerror(int err); /** Create an MDB 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); /** 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. *
    *
  • #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. *
  • #MDB_NOSYNC * Don't perform a synchronous flush after committing a transaction. This means * transactions will exhibit the ACI (atomicity, consistency, and isolation) * properties, but not D (durability); that is database integrity will be * maintained but it is possible some number of the most recently committed * transactions may be undone after a system crash. The number of transactions * at risk is governed by how often the system flushes dirty buffers to disk * and how often #mdb_env_sync() is called. This flag may be changed * at any time using #mdb_env_set_flags(). *
  • #MDB_RDONLY * Open the environment in read-only mode. No write operations will be allowed. *
* @param[in] mode The UNIX permissions to set on created files. This parameter * is ignored on Windows. * @return A non-zero error value on failure and 0 on success. Some possible * errors are: *
    *
  • #MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the * version that created the database environment. *
  • EINVAL - the environment file headers are corrupted. *
  • ENOENT - the directory specified by the path parameter doesn't exist. *
  • EACCES - the user didn't have permission to access the environment files. *
  • EAGAIN - the environment was locked by another process. *
*/ int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode); /** Return statistics about the MDB 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); /** 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. MDB always flushes * the OS buffers upon commit as well, unless the environment was * opened with #MDB_NOSYNC. * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] force If non-zero, force the flush to occur. Otherwise * if the environment has the #MDB_NOSYNC flag set the flushes * will be omitted. * @return A non-zero error value on failure and 0 on success. Some possible * errors are: *
    *
  • EINVAL - an invalid parameter was specified. *
  • EIO - an error occurred during synchronization. *
*/ int mdb_env_sync(MDB_env *env, int force); /** 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); /** Set environment flags. * This may be used to set some flags that weren't already set during * #mdb_env_open(), or to unset these flags. Currently only the * #MDB_NOSYNC flag setting may be changed with this function. * @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: *
    *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff); /** 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: *
    *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_env_get_flags(MDB_env *env, unsigned int *flags); /** 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: *
    *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_env_get_path(MDB_env *env, const char **path); /** 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 accomodate future growth of the database. * 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] size The size in bytes * @return A non-zero error value on failure and 0 on success. Some possible * errors are: *
    *
  • EINVAL - an invalid parameter was specified, or the environment is already open. *
*/ int mdb_env_set_mapsize(MDB_env *env, size_t size); /** Set the maximum number of threads 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. * 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 threads * @return A non-zero error value on failure and 0 on success. Some possible * errors are: *
    *
  • EINVAL - an invalid parameter was specified, or the environment is already open. *
*/ int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers); /** Get the maximum number of threads 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: *
    *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers); /** Set the maximum number of databases for the environment. * This function is only needed if multiple databases will be used in the * environment. Simpler applications that only use a single database can ignore * this option. * 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] dbs The maximum number of databases * @return A non-zero error value on failure and 0 on success. Some possible * errors are: *
    *
  • EINVAL - an invalid parameter was specified, or the environment is already open. *
*/ int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs); /** Create a transaction for use with the environment. * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit(). * @note Transactions may not span threads, a transaction must only be used by a * single thread. * @note Cursors may not span transactions; each cursor must be opened and closed * within a single transaction. * @param[in] env An environment handle returned by #mdb_env_create() * @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. *
    *
  • #MDB_RDONLY * This transaction will not perform any write operations. *
* @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: *
    *
  • #MDB_PANIC - a fatal error occurred earlier and the environment * must be shut down. *
  • ENOMEM - out of memory, or a read-only transaction was requested and * the reader lock table is full. See #mdb_env_set_maxreaders(). *
*/ int mdb_txn_begin(MDB_env *env, unsigned int flags, MDB_txn **txn); /** Commit all the operations of a transaction into the database. * All cursors opened within the transaction must be closed before the transaction * is committed. * The transaction handle will be freed and must not be used again after this call. * @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: *
    *
  • EINVAL - an invalid parameter was specified. *
  • ENOSPC - no more disk space. *
  • EIO - a low-level I/O error occurred while writing. *
*/ int mdb_txn_commit(MDB_txn *txn); /** Abandon all the operations of the transaction instead of saving them. * All cursors opened within the transaction must be closed before the transaction * is aborted. * The transaction handle will be freed and must not be used again after this call. * @param[in] txn A transaction handle returned by #mdb_txn_begin() */ void mdb_txn_abort(MDB_txn *txn); /** Reset a read-only transaction. * This releases the current reader lock but doesn't free the * transaction handle, allowing it to be used again later by #mdb_txn_renew(). * It otherwise has the same effect as #mdb_txn_abort() but saves some memory * allocation/deallocation overhead if a thread is going to start a new * read-only transaction again soon. * All cursors opened within the transaction must be closed before the transaction * is reset. * 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); /** 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: *
    *
  • #MDB_PANIC - a fatal error occurred earlier and the environment * must be shut down. *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_txn_renew(MDB_txn *txn); /** Open a database in the environment. * The database handle may be discarded by calling #mdb_close(). * @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 enviroment, 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. *
    *
  • #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. *
  • #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. *
  • #MDB_INTEGERKEY * Keys are binary integers in native byte order. Setting this option * requires all keys to be the same size, typically sizeof(int) * or sizeof(size_t). *
  • #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 and #MDB_NEXT_MULTIPLE * cursor operations may be used to retrieve multiple items at once. *
  • #MDB_INTEGERDUP * This option specifies that duplicate data items are also integers, and * should be sorted as such. *
  • #MDB_REVERSEDUP * This option specifies that duplicate data items should be compared as * strings in reverse order. *
  • #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. *
* @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: *
    *
  • #MDB_NOTFOUND - the specified database doesn't exist in the environment * and #MDB_CREATE was not specified. *
  • ENFILE - too many databases have been opened. See #mdb_env_set_maxdbs(). *
*/ int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi); /** 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_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: *
    *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat); /** Close a database handle. * 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 any further. * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] dbi A database handle returned by #mdb_open() */ void mdb_close(MDB_env *env, MDB_dbi dbi); /** Delete a database and free all its pages. * This function acquires its own write transaction to perform its * work, so it must not be called if there is already an open write * transaction in the environment. The database handle will also be * closed as part of this operation. * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] dbi A database handle returned by #mdb_open() * @return A non-zero error value on failure and 0 on success. Some possible * errors are: *
    *
  • EINVAL - an invalid parameter was specified. *
  • EBUSY - there is already a write transaction. *
*/ int mdb_drop(MDB_env *env, MDB_dbi dbi); /** 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 speAGAINcial key flags were specified * with #mdb_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_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: *
    *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp); /** 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_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_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: *
    *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp); /** 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_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: *
    *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel); /** 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_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: *
    *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx); /** 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. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_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: *
    *
  • #MDB_NOTFOUND - the key was not in the database. *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data); /** 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_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. *
    *
  • #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. *
  • #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. *
* @return A non-zero error value on failure and 0 on success. Some possible * errors are: *
    *
  • EACCESS - an attempt was made to write in a read-only transaction. *
  • EINVAL - an invalid parameter was specified. *
  • ENOMEM - the database is full, see #mdb_env_set_mapsize(). *
*/ int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data, unsigned int flags); /** 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_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: *
    *
  • EACCESS - an attempt was made to write in a read-only transaction. *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data); /** Create a cursor handle. * Cursors are associated with a specific transaction and database and * may not span threads. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_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: *
    *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor); /** Close a cursor handle. * The cursor handle will be freed and must not be used again after this call. * @param[in] cursor A cursor handle returned by #mdb_cursor_open() */ void mdb_cursor_close(MDB_cursor *cursor); /** 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. * @bug Cursors are not coordinated with write operations. If a cursor in a * write transaction is performing a sequential scan while records are being * inserted or deleted in the same transaction, the cursor will be corrupted. * @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: *
    *
  • #MDB_NOTFOUND - no matching key found. *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data, MDB_cursor_op op); /** Store by cursor. * This function stores key/data pairs into the database. * If the function fails for any reason, the state of the cursor will be * unchanged. If the function succeeds and an item is inserted into the * database, the cursor is always positioned to refer to the newly inserted item. * @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. *
    *
  • #MDB_CURRENT - overwrite the data of the key/data pair to which * the cursor refers with the specified data item. The \b key * parameter is ignored. *
  • #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. *
  • #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). *
* @return A non-zero error value on failure and 0 on success. Some possible * errors are: *
    *
  • EACCES - an attempt was made to modify a read-only database. *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data, unsigned int flags); /** Delete current key/data pair * This function deletes the key/data pair to which the cursor refers. * @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. *
    *
  • #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. *
* @return A non-zero error value on failure and 0 on success. Some possible * errors are: *
    *
  • EACCES - an attempt was made to modify a read-only database. *
  • EINVAL - an invalid parameter was specified. *
*/ int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags); /** 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: *
    *
  • EINVAL - cursor is not initialized, or an invalid parameter was specified. *
*/ int mdb_cursor_count(MDB_cursor *cursor, size_t *countp); /** 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_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); /** Compare two data items according to a particular database. * This returns a comparison as if the two items were data items of * a sorted duplicates #MDB_DUPSORT database. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_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); /** @} */ #endif /* _MDB_H_ */