lmdb-odin/lmdb.odin

/** @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 some systems:
*	  - Windows - automatic
*	  - Linux, systems using POSIX mutexes with Robust option - automatic
*	  - not on BSD, systems using POSIX semaphores.
*	  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_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.
*/
package lmdb

foreign import lib "system:lmdb"

import "core:c"
import "core:fmt"
import "core:sys/posix"

_ :: c

when ODIN_OS == .Windows {
    mode_t :: c.int
} else {
    mode_t :: posix.mode_t
}

when ODIN_OS == .Windows {
    filehandle_t :: rawptr
} else {
    filehandle_t :: c.int
}

Env :: struct {
}

Txn :: struct {
}

/** @brief A handle for an individual database in the DB environment. */
Dbi :: u32

Cursor :: struct {
}

/** @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.
*/
Val :: struct {
	mv_size: uint,   /**< size of the data item */
	mv_data: rawptr, /**< address of the data item */
}

// Automatic `Val` handling for a given type 'T'.
// Will not traverse pointers. If `T` stores pointers, you probably don't want to use this.
Auto_Val :: struct($T: typeid) {
    raw: Val
}

autoval :: #force_inline proc "contextless" (val_ptr: ^$T) -> Auto_Val(T) {
    return Auto_Val(T){Val{size_of(T), val_ptr}}
}

nil_autoval :: #force_inline proc "contextless" ($T: typeid) -> Auto_Val(T) {
    return Auto_Val(T){Val{size_of(T), nil}}
}

autoval_get_data :: #force_inline proc "contextless" (val: ^Auto_Val($T)) -> ^T {
    return cast(^T)val.raw.mv_data
}

// Panic if there is an error
panic_on_err :: #force_inline proc(error: Error) {
    if error != .NONE {
        fmt.panicf("Irrecoverable LMDB error", strerror(i32(error)))
    }
}

/** @brief A callback function used to compare two keys in a database */
Cmp_Func :: #type proc "c" (^Val, ^Val) -> i32

/** @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.
*/
Rel_Func :: #type proc "c" (item: ^Val, oldptr, newptr, relctx: rawptr)

/** @defgroup	mdb_env	Environment Flags
 *	@{
 */
	/** mmap at a fixed address (experimental) */
ENV_FIXEDMAP ::	0x01
	/** no environment directory */
ENV_NOSUBDIR ::	0x4000
	/** don't fsync after commit */
ENV_NOSYNC ::		0x10000
	/** read only */
ENV_RDONLY ::		0x20000
	/** don't fsync metapage after commit */
ENV_NOMETASYNC ::		0x40000
	/** use writable mmap */
ENV_WRITEMAP ::		0x80000
	/** use asynchronous msync when #MDB_WRITEMAP is used */
ENV_MAPASYNC ::		0x100000
	/** tie reader locktable slots to #MDB_txn objects instead of to threads */
ENV_NOTLS ::		0x200000
	/** don't do any locking, caller must manage their own locks */
ENV_NOLOCK ::		0x400000
	/** don't do readahead (no effect on Windows) */
ENV_NORDAHEAD ::	0x800000
	/** don't initialize malloc'd memory before writing to datafile */
ENV_NOMEMINIT ::	0x1000000
/** @} */

/**	@defgroup	mdb_dbi_open	Database Flags
 *	@{
 */
	/** use reverse string keys */
DB_REVERSEKEY ::	0x02
	/** use sorted duplicates */
DB_DUPSORT ::		0x04
	/** numeric keys in native byte order: either unsigned int or size_t.
	 *  The keys must all be of the same size. */
DB_INTEGERKEY ::	0x08
	/** with #MDB_DUPSORT, sorted dup items have fixed size */
DB_DUPFIXED ::	0x10
	/** with #MDB_DUPSORT, dups are #MDB_INTEGERKEY-style integers */
DB_INTEGERDUP ::	0x20
	/** with #MDB_DUPSORT, use reverse string dups */
DB_REVERSEDUP ::	0x40
	/** create DB if not already existing */
DB_CREATE ::		0x40000
/** @} */

/**	@defgroup mdb_put	Write Flags
 *	@{
 */
/** For put: Don't write if the key already exists. */
WRITE_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.
 */
WRITE_NODUPDATA ::	0x20
/** For mdb_cursor_put: overwrite the current key/data pair */
WRITE_CURRENT ::	0x40
/** For put: Just reserve space for data, don't copy it. Return a
 * pointer to the reserved space.
 */
WRITE_RESERVE ::	0x10000
/** Data is being appended, don't split full pages. */
WRITE_APPEND ::	0x20000
/** Duplicate data is being appended, don't split full pages. */
WRITE_APPENDDUP ::	0x40000
/** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
WRITE_MULTIPLE ::	0x80000
/*	@} */

/**	@defgroup mdb_copy	Copy Flags
 *	@{
 */
/** Compacting copy: Omit free space from copy, and renumber all
 * pages sequentially.
 */
CP_COMPACT ::	0x01
/*	@} */

/** @brief Cursor Get operations.
*
*	This is the set of all operations for retrieving data
*	using a cursor.
*/
Cursor_Op :: enum c.int {
	FIRST,          /**< Position at first key/data item */
	FIRST_DUP,      /**< Position at first data item of current key.
								Only for #MDB_DUPSORT */
	GET_BOTH,       /**< Position at key/data pair. Only for #MDB_DUPSORT */
	GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
	GET_CURRENT,    /**< Return key/data at current cursor position */
	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 */
	LAST,           /**< Position at last key/data item */
	LAST_DUP,       /**< Position at last data item of current key.
								Only for #MDB_DUPSORT */
	NEXT,           /**< Position at next data item */
	NEXT_DUP,       /**< Position at next data item of current key.
								Only for #MDB_DUPSORT */
	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 */
	NEXT_NODUP,     /**< Position at first data item of next key */
	PREV,           /**< Position at previous data item */
	PREV_DUP,       /**< Position at previous data item of current key.
								Only for #MDB_DUPSORT */
	PREV_NODUP,     /**< Position at last data item of previous key */
	SET,            /**< Position at specified key */
	SET_KEY,        /**< Position at specified key, return key + data */
	SET_RANGE,      /**< Position at first key greater than or equal to specified key. */
	PREV_MULTIPLE,  /**< Position at previous page and return up to
								a page of duplicate data items. Only for #MDB_DUPFIXED */
}

Error :: enum c.int {
    /**	Successful result */
    NONE = 0,
    /** key/data pair already exists */
    KEYEXIST = -30799,
    /** key/data pair not found (EOF) */
    NOTFOUND = -30798,
    /** Requested page not found - this usually indicates corruption */
    PAGE_NOTFOUND = -30797,
    /** Located page was wrong type */
    CORRUPTED = -30796,
    /** Update of meta page failed or environment had fatal error */
    PANIC = -30795,
    /** Environment version mismatch */
    VERSION_MISMATCH = -30794,
    /** File is not a valid LMDB file */
    INVALID = -30793,
    /** Environment mapsize reached */
    MAP_FULL = -30792,
    /** Environment maxdbs reached */
    DBS_FULL = -30791,
    /** Environment maxreaders reached */
    READERS_FULL = -30790,
    /** Too many TLS keys in use - Windows only */
    TLS_FULL = -30789,
    /** Txn has too many dirty pages */
    TXN_FULL = -30788,
    /** Cursor stack too deep - internal error */
    CURSOR_FULL = -30787,
    /** Page has not enough space - internal error */
    PAGE_FULL = -30786,
    /** Database contents grew beyond environment mapsize */
    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>
	 */
    INCOMPATIBLE = -30784,
    /** Invalid reuse of reader locktable slot */
    BAD_RSLOT = -30783,
    /** Transaction must abort, has a child, or is invalid */
    BAD_TXN = -30782,
    /** Unsupported size of key/DB name/data, or wrong DUPFIXED size */
    BAD_VALSIZE = -30781,
    /** The specified DBI was changed unexpectedly */
    BAD_DBI = -30780,
}

/** @brief Statistics for a database in the environment */
Stat :: struct {
	ms_psize:          u32,  /**< Size of a database page.
											This is currently the same for all databases. */
	ms_depth:          u32,  /**< Depth (height) of the B-tree */
	ms_branch_pages:   uint, /**< Number of internal (non-leaf) pages */
	ms_leaf_pages:     uint, /**< Number of leaf pages */
	ms_overflow_pages: uint, /**< Number of overflow pages */
	ms_entries:        uint, /**< Number of data items */
}

/** @brief Information about the environment */
Env_Info :: struct {
	me_mapaddr:    rawptr, /**< Address of map, if fixed */
	me_mapsize:    uint,   /**< Size of the data memory map */
	me_last_pgno:  uint,   /**< ID of the last used page */
	me_last_txnid: uint,   /**< ID of the last committed transaction */
	me_maxreaders: u32,    /**< max reader slots in the environment */
	me_numreaders: u32,    /**< max reader slots used in the environment */
}

/** @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.
*/
Assert_Func :: proc "c" (^Env, cstring)

/** @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.
*/
Msg_Func :: proc "c" (cstring, rawptr) -> i32

@(default_calling_convention="c", link_prefix="mdb_")
foreign lib {
	/** @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
	*/
	version :: proc(major: ^i32, minor: ^i32, patch: ^i32) -> cstring ---

	/** @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
	*/
	strerror :: proc(err: i32) -> cstring ---

	/** @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.
	*/
	@(require_results)
	env_create :: proc(env: ^^Env) -> Error ---

	/** @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().
	* </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>
	*/
	@(require_results)
	env_open :: proc(env: ^Env, path: cstring, flags: u32, mode: mode_t) -> Error ---

	/** @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.
	*/
	@(require_results)
	env_copy :: proc(env: ^Env, path: cstring) -> Error ---

	/** @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.
	*/
	@(require_results)
	env_copyfd :: proc(env: ^Env, fd: filehandle_t) -> Error ---

	/** @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.
	*/
	@(require_results)
	env_copy2 :: proc(env: ^Env, path: cstring, flags: u32) -> Error ---

	/** @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.
	*/
	@(require_results)
	env_copyfd2 :: proc(env: ^Env, fd: filehandle_t, flags: u32) -> Error ---

	/** @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
	*/
	env_stat :: proc(env: ^Env, stat: ^Stat) -> i32 ---

	/** @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
	*/
	env_info :: proc(env: ^Env, stat: ^Env_Info) -> i32 ---

	/** @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>
	*/
	@(require_results)
	env_sync :: proc(env: ^Env, force: i32) -> Error ---

	/** @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()
	*/
	env_close :: proc(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>
	*/
	@(require_results)
	env_set_flags :: proc(env: ^Env, flags: u32, onoff: i32) -> Error ---

	/** @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>
	*/
	@(require_results)
	env_get_flags :: proc(env: ^Env, flags: ^u32) -> Error ---

	/** @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>
	*/
	@(require_results)
	env_get_path :: proc(env: ^Env, path: ^^u8) -> Error ---

	/** @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>
	*/
	@(require_results)
	env_get_fd :: proc(env: ^Env, fd: ^filehandle_t) -> Error ---

	/** @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>
	*/
	@(require_results)
	env_set_mapsize :: proc(env: ^Env, size: uint) -> Error ---

	/** @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>
	*/
	@(require_results)
	env_set_maxreaders :: proc(env: ^Env, readers: u32) -> Error ---

	/** @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>
	*/
	@(require_results)
	env_get_maxreaders :: proc(env: ^Env, readers: ^u32) -> Error ---

	/** @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>
	*/
	@(require_results)
	env_set_maxdbs :: proc(env: ^Env, dbs: Dbi) -> Error ---

	/** @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
	*/
	env_get_maxkeysize :: proc(env: ^Env) -> i32 ---

	/** @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.
	*/
	@(require_results)
	env_set_userctx :: proc(env: ^Env, ctx: rawptr) -> Error ---

	/** @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().
	*/
	env_get_userctx :: proc(env: ^Env) -> rawptr ---

	/** 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.
	*/
	@(require_results)
	env_set_assert :: proc(env: ^Env, func: Assert_Func) -> Error ---

	/** @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.
	* </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>
	*/
	@(require_results)
	txn_begin :: proc(env: ^Env, parent: ^Txn, flags: u32, txn: ^^Txn) -> Error ---

	/** @brief Returns the transaction's #MDB_env
	*
	* @param[in] txn A transaction handle returned by #mdb_txn_begin()
	*/
	txn_env :: proc(txn: ^Txn) -> ^Env ---

	/** @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.
	*/
	txn_id :: proc(txn: ^Txn) -> uint ---

	/** @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>
	*/
	@(require_results)
	txn_commit :: proc(txn: ^Txn) -> Error ---

	/** @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()
	*/
	txn_abort :: proc(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()
	*/
	txn_reset :: proc(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>
	*/
	@(require_results)
	txn_renew :: proc(txn: ^Txn) -> Error ---

	/** @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 size_t, and will be sorted as such.
	*		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>
	*/
	@(require_results)
	dbi_open :: proc(txn: ^Txn, name: cstring, flags: u32, dbi: ^Dbi) -> Error ---

	/** @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>
	*/
	@(require_results)
	stat :: proc(txn: ^Txn, dbi: Dbi, stat: ^Stat) -> Error ---

	/** @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.
	*/
	@(require_results)
	dbi_flags :: proc(txn: ^Txn, dbi: Dbi, flags: ^u32) -> Error ---

	/** @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()
	*/
	dbi_close :: proc(env: ^Env, 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.
	*/
	@(require_results)
	drop :: proc(txn: ^Txn, dbi: Dbi, del: i32) -> Error ---

	/** @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>
	*/
	@(require_results)
	set_compare :: proc(txn: ^Txn, dbi: Dbi, cmp: Cmp_Func) -> Error ---

	/** @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>
	*/
	@(require_results)
	set_dupsort :: proc(txn: ^Txn, dbi: Dbi, cmp: Cmp_Func) -> Error ---

	/** @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>
	*/
	@(require_results)
	set_relfunc :: proc(txn: ^Txn, dbi: Dbi, rel: Rel_Func) -> Error ---

	/** @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>
	*/
	@(require_results)
	set_relctx :: proc(txn: ^Txn, dbi: Dbi, ctx: rawptr) -> Error ---

	/** @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>
	*/
	@(require_results)
	get :: proc(txn: ^Txn, dbi: Dbi, key: ^Val, data: ^Val) -> Error ---

	/** @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>
	*/
	@(require_results)
	put :: proc(txn: ^Txn, dbi: Dbi, key: ^Val, data: ^Val, flags: u32) -> Error ---

	/** @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>
	*/
	@(require_results)
	del :: proc(txn: ^Txn, dbi: Dbi, key: ^Val, data: ^Val) -> Error ---

	/** @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>
	*/
	@(require_results)
	cursor_open :: proc(txn: ^Txn, dbi: Dbi, cursor: ^^Cursor) -> Error ---

	/** @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()
	*/
	cursor_close :: proc(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>
	*/
	@(require_results)
	cursor_renew :: proc(txn: ^Txn, cursor: ^Cursor) -> Error ---

	/** @brief Return the cursor's transaction handle.
	*
	* @param[in] cursor A cursor handle returned by #mdb_cursor_open()
	*/
	cursor_txn :: proc(cursor: ^Cursor) -> ^Txn ---

	/** @brief Return the cursor's database handle.
	*
	* @param[in] cursor A cursor handle returned by #mdb_cursor_open()
	*/
	cursor_dbi :: proc(cursor: ^Cursor) -> Dbi ---

	/** @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>
	*/
	@(require_results)
	cursor_get :: proc(cursor: ^Cursor, key: ^Val, data: ^Val, op: Cursor_Op) -> Error ---

	/** @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>
	*/
	@(require_results)
	cursor_put :: proc(cursor: ^Cursor, key: ^Val, data: ^Val, flags: u32) -> Error ---

	/** @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>
	*/
	@(require_results)
	cursor_del :: proc(cursor: ^Cursor, flags: u32) -> Error ---

	/** @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>
	*/
	@(require_results)
	cursor_count :: proc(cursor: ^Cursor, countp: ^uint) -> Error ---

	/** @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
	*/
	cmp :: proc(txn: ^Txn, dbi: Dbi, a: ^Val, b: ^Val) -> i32 ---

	/** @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
	*/
	dcmp :: proc(txn: ^Txn, dbi: Dbi, a: ^Val, b: ^Val) -> i32 ---

	/** @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.
	*/
	reader_list :: proc(env: ^Env, func: Msg_Func, ctx: rawptr) -> i32 ---

	/** @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.
	*/
	@(require_results)
	reader_check :: proc(env: ^Env, dead: ^i32) -> Error ---
}