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mdb.c
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mdb.c
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/** @file mdb.c
* @brief Lightning memory-mapped database library
*
* A Btree-based database management library modeled loosely on the
* BerkeleyDB API, but much simplified.
*/
/*
* 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>.
*
* This code is derived from btree.c written by Martin Hedenfalk.
*
* Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#if defined(MDB_VL32) || defined(__WIN64__)
#define _FILE_OFFSET_BITS 64
#endif
#ifdef _WIN32
#include <malloc.h>
#include <windows.h>
#include <wchar.h> /* get wcscpy() */
/* We use native NT APIs to setup the memory map, so that we can
* let the DB file grow incrementally instead of always preallocating
* the full size. These APIs are defined in <wdm.h> and <ntifs.h>
* but those headers are meant for driver-level development and
* conflict with the regular user-level headers, so we explicitly
* declare them here. We get pointers to these functions from
* NTDLL.DLL at runtime, to avoid buildtime dependencies on any
* NTDLL import libraries.
*/
typedef NTSTATUS (WINAPI NtCreateSectionFunc)
(OUT PHANDLE sh, IN ACCESS_MASK acc,
IN void * oa OPTIONAL,
IN PLARGE_INTEGER ms OPTIONAL,
IN ULONG pp, IN ULONG aa, IN HANDLE fh OPTIONAL);
static NtCreateSectionFunc *NtCreateSection;
typedef enum _SECTION_INHERIT {
ViewShare = 1,
ViewUnmap = 2
} SECTION_INHERIT;
typedef NTSTATUS (WINAPI NtMapViewOfSectionFunc)
(IN PHANDLE sh, IN HANDLE ph,
IN OUT PVOID *addr, IN ULONG_PTR zbits,
IN SIZE_T cs, IN OUT PLARGE_INTEGER off OPTIONAL,
IN OUT PSIZE_T vs, IN SECTION_INHERIT ih,
IN ULONG at, IN ULONG pp);
static NtMapViewOfSectionFunc *NtMapViewOfSection;
typedef NTSTATUS (WINAPI NtCloseFunc)(HANDLE h);
static NtCloseFunc *NtClose;
/** getpid() returns int; MinGW defines pid_t but MinGW64 typedefs it
* as int64 which is wrong. MSVC doesn't define it at all, so just
* don't use it.
*/
#define MDB_PID_T int
#define MDB_THR_T DWORD
#include <sys/types.h>
#include <sys/stat.h>
#ifdef __GNUC__
# include <sys/param.h>
#else
# define LITTLE_ENDIAN 1234
# define BIG_ENDIAN 4321
# define BYTE_ORDER LITTLE_ENDIAN
# ifndef SSIZE_MAX
# define SSIZE_MAX INT_MAX
# endif
#endif
#define MDB_OFF_T int64_t
#else
#include <sys/types.h>
#include <sys/stat.h>
#define MDB_PID_T pid_t
#define MDB_THR_T pthread_t
#include <sys/param.h>
#include <sys/uio.h>
#include <sys/mman.h>
#ifdef HAVE_SYS_FILE_H
#include <sys/file.h>
#endif
#include <fcntl.h>
#define MDB_OFF_T off_t
#endif
#if defined(__mips) && defined(__linux)
/* MIPS has cache coherency issues, requires explicit cache control */
#include <sys/cachectl.h>
#define CACHEFLUSH(addr, bytes, cache) cacheflush(addr, bytes, cache)
#else
#define CACHEFLUSH(addr, bytes, cache)
#endif
#if defined(__linux) && !defined(MDB_FDATASYNC_WORKS)
/** fdatasync is broken on ext3/ext4fs on older kernels, see
* description in #mdb_env_open2 comments. You can safely
* define MDB_FDATASYNC_WORKS if this code will only be run
* on kernels 3.6 and newer.
*/
#define BROKEN_FDATASYNC
#endif
#include <errno.h>
#include <limits.h>
#include <stddef.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#ifdef _MSC_VER
#include <io.h>
typedef SSIZE_T ssize_t;
#else
#include <unistd.h>
#endif
#if defined(__sun) || defined(__ANDROID__)
/* Most platforms have posix_memalign, older may only have memalign */
#define HAVE_MEMALIGN 1
#include <malloc.h>
/* On Solaris, we need the POSIX sigwait function */
#if defined (__sun)
# define _POSIX_PTHREAD_SEMANTICS 1
#endif
#endif
#if !(defined(BYTE_ORDER) || defined(__BYTE_ORDER))
#include <netinet/in.h>
#include <resolv.h> /* defines BYTE_ORDER on HPUX and Solaris */
#endif
#if defined(__FreeBSD__) && defined(__FreeBSD_version) && __FreeBSD_version >= 1100110
# define MDB_USE_POSIX_MUTEX 1
# define MDB_USE_ROBUST 1
#elif defined(__APPLE__) || defined (BSD) || defined(__FreeBSD_kernel__)
# if !(defined(MDB_USE_POSIX_MUTEX) || defined(MDB_USE_POSIX_SEM))
# define MDB_USE_SYSV_SEM 1
# endif
# define MDB_FDATASYNC fsync
#elif defined(__ANDROID__)
# define MDB_FDATASYNC fsync
#endif
#ifndef _WIN32
#include <pthread.h>
#include <signal.h>
#ifdef MDB_USE_POSIX_SEM
# define MDB_USE_HASH 1
#include <semaphore.h>
#elif defined(MDB_USE_SYSV_SEM)
#include <sys/ipc.h>
#include <sys/sem.h>
#ifdef _SEM_SEMUN_UNDEFINED
union semun {
int val;
struct semid_ds *buf;
unsigned short *array;
};
#endif /* _SEM_SEMUN_UNDEFINED */
#else
#define MDB_USE_POSIX_MUTEX 1
#endif /* MDB_USE_POSIX_SEM */
#endif /* !_WIN32 */
#if defined(_WIN32) + defined(MDB_USE_POSIX_SEM) + defined(MDB_USE_SYSV_SEM) \
+ defined(MDB_USE_POSIX_MUTEX) != 1
# error "Ambiguous shared-lock implementation"
#endif
#ifdef USE_VALGRIND
#include <valgrind/memcheck.h>
#define VGMEMP_CREATE(h,r,z) VALGRIND_CREATE_MEMPOOL(h,r,z)
#define VGMEMP_ALLOC(h,a,s) VALGRIND_MEMPOOL_ALLOC(h,a,s)
#define VGMEMP_FREE(h,a) VALGRIND_MEMPOOL_FREE(h,a)
#define VGMEMP_DESTROY(h) VALGRIND_DESTROY_MEMPOOL(h)
#define VGMEMP_DEFINED(a,s) VALGRIND_MAKE_MEM_DEFINED(a,s)
#else
#define VGMEMP_CREATE(h,r,z)
#define VGMEMP_ALLOC(h,a,s)
#define VGMEMP_FREE(h,a)
#define VGMEMP_DESTROY(h)
#define VGMEMP_DEFINED(a,s)
#endif
#ifndef BYTE_ORDER
# if (defined(_LITTLE_ENDIAN) || defined(_BIG_ENDIAN)) && !(defined(_LITTLE_ENDIAN) && defined(_BIG_ENDIAN))
/* Solaris just defines one or the other */
# define LITTLE_ENDIAN 1234
# define BIG_ENDIAN 4321
# ifdef _LITTLE_ENDIAN
# define BYTE_ORDER LITTLE_ENDIAN
# else
# define BYTE_ORDER BIG_ENDIAN
# endif
# else
# define BYTE_ORDER __BYTE_ORDER
# endif
#endif
#ifndef LITTLE_ENDIAN
#define LITTLE_ENDIAN __LITTLE_ENDIAN
#endif
#ifndef BIG_ENDIAN
#define BIG_ENDIAN __BIG_ENDIAN
#endif
#if defined(__i386) || defined(__x86_64) || defined(_M_IX86)
#define MISALIGNED_OK 1
#endif
#include "lmdb.h"
#include "midl.h"
#if (BYTE_ORDER == LITTLE_ENDIAN) == (BYTE_ORDER == BIG_ENDIAN)
# error "Unknown or unsupported endianness (BYTE_ORDER)"
#elif (-6 & 5) || CHAR_BIT!=8 || UINT_MAX!=0xffffffff || MDB_SIZE_MAX%UINT_MAX
# error "Two's complement, reasonably sized integer types, please"
#endif
#if (((__clang_major__ << 8) | __clang_minor__) >= 0x0302) || (((__GNUC__ << 8) | __GNUC_MINOR__) >= 0x0403)
/** Mark infrequently used env functions as cold. This puts them in a separate
* section, and optimizes them for size */
#define ESECT __attribute__ ((cold))
#else
/* On older compilers, use a separate section */
# ifdef __GNUC__
# ifdef __APPLE__
# define ESECT __attribute__ ((section("__TEXT,text_env")))
# else
# define ESECT __attribute__ ((section("text_env")))
# endif
# else
# define ESECT
# endif
#endif
#ifdef _WIN32
#define CALL_CONV WINAPI
#else
#define CALL_CONV
#endif
/** @defgroup internal LMDB Internals
* @{
*/
/** @defgroup compat Compatibility Macros
* A bunch of macros to minimize the amount of platform-specific ifdefs
* needed throughout the rest of the code. When the features this library
* needs are similar enough to POSIX to be hidden in a one-or-two line
* replacement, this macro approach is used.
* @{
*/
/** Features under development */
#ifndef MDB_DEVEL
#define MDB_DEVEL 0
#endif
/** Wrapper around __func__, which is a C99 feature */
#if __STDC_VERSION__ >= 199901L
# define mdb_func_ __func__
#elif __GNUC__ >= 2 || _MSC_VER >= 1300
# define mdb_func_ __FUNCTION__
#else
/* If a debug message says <mdb_unknown>(), update the #if statements above */
# define mdb_func_ "<mdb_unknown>"
#endif
/* Internal error codes, not exposed outside liblmdb */
#define MDB_NO_ROOT (MDB_LAST_ERRCODE + 10)
#ifdef _WIN32
#define MDB_OWNERDEAD ((int) WAIT_ABANDONED)
#elif defined MDB_USE_SYSV_SEM
#define MDB_OWNERDEAD (MDB_LAST_ERRCODE + 11)
#elif defined(MDB_USE_POSIX_MUTEX) && defined(EOWNERDEAD)
#define MDB_OWNERDEAD EOWNERDEAD /**< #LOCK_MUTEX0() result if dead owner */
#endif
#ifdef __GLIBC__
#define GLIBC_VER ((__GLIBC__ << 16 )| __GLIBC_MINOR__)
#endif
/** Some platforms define the EOWNERDEAD error code
* even though they don't support Robust Mutexes.
* Compile with -DMDB_USE_ROBUST=0, or use some other
* mechanism like -DMDB_USE_SYSV_SEM instead of
* -DMDB_USE_POSIX_MUTEX. (SysV semaphores are
* also Robust, but some systems don't support them
* either.)
*/
#ifndef MDB_USE_ROBUST
/* Android currently lacks Robust Mutex support. So does glibc < 2.4. */
# if defined(MDB_USE_POSIX_MUTEX) && (defined(__ANDROID__) || \
(defined(__GLIBC__) && GLIBC_VER < 0x020004))
# define MDB_USE_ROBUST 0
# else
# define MDB_USE_ROBUST 1
# endif
#endif /* !MDB_USE_ROBUST */
#if defined(MDB_USE_POSIX_MUTEX) && (MDB_USE_ROBUST)
/* glibc < 2.12 only provided _np API */
# if (defined(__GLIBC__) && GLIBC_VER < 0x02000c) || \
(defined(PTHREAD_MUTEX_ROBUST_NP) && !defined(PTHREAD_MUTEX_ROBUST))
# define PTHREAD_MUTEX_ROBUST PTHREAD_MUTEX_ROBUST_NP
# define pthread_mutexattr_setrobust(attr, flag) pthread_mutexattr_setrobust_np(attr, flag)
# define pthread_mutex_consistent(mutex) pthread_mutex_consistent_np(mutex)
# endif
#endif /* MDB_USE_POSIX_MUTEX && MDB_USE_ROBUST */
#if defined(MDB_OWNERDEAD) && (MDB_USE_ROBUST)
#define MDB_ROBUST_SUPPORTED 1
#endif
#ifdef _WIN32
#define MDB_USE_HASH 1
#define MDB_PIDLOCK 0
#define THREAD_RET DWORD
#define pthread_t HANDLE
#define pthread_mutex_t HANDLE
#define pthread_cond_t HANDLE
typedef HANDLE mdb_mutex_t, mdb_mutexref_t;
#define pthread_key_t DWORD
#define pthread_self() GetCurrentThreadId()
#define pthread_key_create(x,y) \
((*(x) = TlsAlloc()) == TLS_OUT_OF_INDEXES ? ErrCode() : 0)
#define pthread_key_delete(x) TlsFree(x)
#define pthread_getspecific(x) TlsGetValue(x)
#define pthread_setspecific(x,y) (TlsSetValue(x,y) ? 0 : ErrCode())
#define pthread_mutex_unlock(x) ReleaseMutex(*x)
#define pthread_mutex_lock(x) WaitForSingleObject(*x, INFINITE)
#define pthread_cond_signal(x) SetEvent(*x)
#define pthread_cond_wait(cond,mutex) do{SignalObjectAndWait(*mutex, *cond, INFINITE, FALSE); WaitForSingleObject(*mutex, INFINITE);}while(0)
#define THREAD_CREATE(thr,start,arg) \
(((thr) = CreateThread(NULL, 0, start, arg, 0, NULL)) ? 0 : ErrCode())
#define THREAD_FINISH(thr) \
(WaitForSingleObject(thr, INFINITE) ? ErrCode() : 0)
#define LOCK_MUTEX0(mutex) WaitForSingleObject(mutex, INFINITE)
#define UNLOCK_MUTEX(mutex) ReleaseMutex(mutex)
#define mdb_mutex_consistent(mutex) 0
#define getpid() GetCurrentProcessId()
#define MDB_FDATASYNC(fd) (!FlushFileBuffers(fd))
#define MDB_MSYNC(addr,len,flags) (!FlushViewOfFile(addr,len))
#define ErrCode() GetLastError()
#define GET_PAGESIZE(x) {SYSTEM_INFO si; GetSystemInfo(&si); (x) = si.dwPageSize;}
#define close(fd) (CloseHandle(fd) ? 0 : -1)
#define munmap(ptr,len) UnmapViewOfFile(ptr)
#ifdef PROCESS_QUERY_LIMITED_INFORMATION
#define MDB_PROCESS_QUERY_LIMITED_INFORMATION PROCESS_QUERY_LIMITED_INFORMATION
#else
#define MDB_PROCESS_QUERY_LIMITED_INFORMATION 0x1000
#endif
#else
#define THREAD_RET void *
#define THREAD_CREATE(thr,start,arg) pthread_create(&thr,NULL,start,arg)
#define THREAD_FINISH(thr) pthread_join(thr,NULL)
/** For MDB_LOCK_FORMAT: True if readers take a pid lock in the lockfile */
#define MDB_PIDLOCK 1
#ifdef MDB_USE_POSIX_SEM
typedef sem_t *mdb_mutex_t, *mdb_mutexref_t;
#define LOCK_MUTEX0(mutex) mdb_sem_wait(mutex)
#define UNLOCK_MUTEX(mutex) sem_post(mutex)
static int
mdb_sem_wait(sem_t *sem)
{
int rc;
while ((rc = sem_wait(sem)) && (rc = errno) == EINTR) ;
return rc;
}
#elif defined MDB_USE_SYSV_SEM
typedef struct mdb_mutex {
int semid;
int semnum;
int *locked;
} mdb_mutex_t[1], *mdb_mutexref_t;
#define LOCK_MUTEX0(mutex) mdb_sem_wait(mutex)
#define UNLOCK_MUTEX(mutex) do { \
struct sembuf sb = { 0, 1, SEM_UNDO }; \
sb.sem_num = (mutex)->semnum; \
*(mutex)->locked = 0; \
semop((mutex)->semid, &sb, 1); \
} while(0)
static int
mdb_sem_wait(mdb_mutexref_t sem)
{
int rc, *locked = sem->locked;
struct sembuf sb = { 0, -1, SEM_UNDO };
sb.sem_num = sem->semnum;
do {
if (!semop(sem->semid, &sb, 1)) {
rc = *locked ? MDB_OWNERDEAD : MDB_SUCCESS;
*locked = 1;
break;
}
} while ((rc = errno) == EINTR);
return rc;
}
#define mdb_mutex_consistent(mutex) 0
#else /* MDB_USE_POSIX_MUTEX: */
/** Shared mutex/semaphore as the original is stored.
*
* Not for copies. Instead it can be assigned to an #mdb_mutexref_t.
* When mdb_mutexref_t is a pointer and mdb_mutex_t is not, then it
* is array[size 1] so it can be assigned to the pointer.
*/
typedef pthread_mutex_t mdb_mutex_t[1];
/** Reference to an #mdb_mutex_t */
typedef pthread_mutex_t *mdb_mutexref_t;
/** Lock the reader or writer mutex.
* Returns 0 or a code to give #mdb_mutex_failed(), as in #LOCK_MUTEX().
*/
#define LOCK_MUTEX0(mutex) pthread_mutex_lock(mutex)
/** Unlock the reader or writer mutex.
*/
#define UNLOCK_MUTEX(mutex) pthread_mutex_unlock(mutex)
/** Mark mutex-protected data as repaired, after death of previous owner.
*/
#define mdb_mutex_consistent(mutex) pthread_mutex_consistent(mutex)
#endif /* MDB_USE_POSIX_SEM || MDB_USE_SYSV_SEM */
/** Get the error code for the last failed system function.
*/
#define ErrCode() errno
/** An abstraction for a file handle.
* On POSIX systems file handles are small integers. On Windows
* they're opaque pointers.
*/
#define HANDLE int
/** A value for an invalid file handle.
* Mainly used to initialize file variables and signify that they are
* unused.
*/
#define INVALID_HANDLE_VALUE (-1)
/** Get the size of a memory page for the system.
* This is the basic size that the platform's memory manager uses, and is
* fundamental to the use of memory-mapped files.
*/
#define GET_PAGESIZE(x) ((x) = sysconf(_SC_PAGE_SIZE))
#endif
#define Z MDB_FMT_Z /**< printf/scanf format modifier for size_t */
#define Yu MDB_PRIy(u) /**< printf format for #mdb_size_t */
#define Yd MDB_PRIy(d) /**< printf format for 'signed #mdb_size_t' */
#ifdef MDB_USE_SYSV_SEM
#define MNAME_LEN (sizeof(int))
#else
#define MNAME_LEN (sizeof(pthread_mutex_t))
#endif
/** Initial part of #MDB_env.me_mutexname[].
* Changes to this code must be reflected in #MDB_LOCK_FORMAT.
*/
#ifdef _WIN32
#define MUTEXNAME_PREFIX "Global\\MDB"
#elif defined MDB_USE_POSIX_SEM
#define MUTEXNAME_PREFIX "/MDB"
#endif
/** @} */
#ifdef MDB_ROBUST_SUPPORTED
/** Lock mutex, handle any error, set rc = result.
* Return 0 on success, nonzero (not rc) on error.
*/
#define LOCK_MUTEX(rc, env, mutex) \
(((rc) = LOCK_MUTEX0(mutex)) && \
((rc) = mdb_mutex_failed(env, mutex, rc)))
static int mdb_mutex_failed(MDB_env *env, mdb_mutexref_t mutex, int rc);
#else
#define LOCK_MUTEX(rc, env, mutex) ((rc) = LOCK_MUTEX0(mutex))
#define mdb_mutex_failed(env, mutex, rc) (rc)
#endif
#ifndef _WIN32
/** A flag for opening a file and requesting synchronous data writes.
* This is only used when writing a meta page. It's not strictly needed;
* we could just do a normal write and then immediately perform a flush.
* But if this flag is available it saves us an extra system call.
*
* @note If O_DSYNC is undefined but exists in /usr/include,
* preferably set some compiler flag to get the definition.
*/
#ifndef MDB_DSYNC
# ifdef O_DSYNC
# define MDB_DSYNC O_DSYNC
# else
# define MDB_DSYNC O_SYNC
# endif
#endif
#endif
/** Function for flushing the data of a file. Define this to fsync
* if fdatasync() is not supported.
*/
#ifndef MDB_FDATASYNC
# define MDB_FDATASYNC fdatasync
#endif
#ifndef MDB_MSYNC
# define MDB_MSYNC(addr,len,flags) msync(addr,len,flags)
#endif
#ifndef MS_SYNC
#define MS_SYNC 1
#endif
#ifndef MS_ASYNC
#define MS_ASYNC 0
#endif
/** A page number in the database.
* Note that 64 bit page numbers are overkill, since pages themselves
* already represent 12-13 bits of addressable memory, and the OS will
* always limit applications to a maximum of 63 bits of address space.
*
* @note In the #MDB_node structure, we only store 48 bits of this value,
* which thus limits us to only 60 bits of addressable data.
*/
typedef MDB_ID pgno_t;
/** A transaction ID.
* See struct MDB_txn.mt_txnid for details.
*/
typedef MDB_ID txnid_t;
/** @defgroup debug Debug Macros
* @{
*/
#ifndef MDB_DEBUG
/** Enable debug output. Needs variable argument macros (a C99 feature).
* Set this to 1 for copious tracing. Set to 2 to add dumps of all IDLs
* read from and written to the database (used for free space management).
*/
#define MDB_DEBUG 0
#endif
#if MDB_DEBUG
static int mdb_debug;
static txnid_t mdb_debug_start;
/** Print a debug message with printf formatting.
* Requires double parenthesis around 2 or more args.
*/
# define DPRINTF(args) ((void) ((mdb_debug) && DPRINTF0 args))
# define DPRINTF0(fmt, ...) \
fprintf(stderr, "%s:%d " fmt "\n", mdb_func_, __LINE__, __VA_ARGS__)
#else
# define DPRINTF(args) ((void) 0)
#endif
/** Print a debug string.
* The string is printed literally, with no format processing.
*/
#define DPUTS(arg) DPRINTF(("%s", arg))
/** Debugging output value of a cursor DBI: Negative in a sub-cursor. */
#define DDBI(mc) \
(((mc)->mc_flags & C_SUB) ? -(int)(mc)->mc_dbi : (int)(mc)->mc_dbi)
/** @} */
/** @brief The maximum size of a database page.
*
* It is 32k or 64k, since value-PAGEBASE must fit in
* #MDB_page.%mp_upper.
*
* LMDB will use database pages < OS pages if needed.
* That causes more I/O in write transactions: The OS must
* know (read) the whole page before writing a partial page.
*
* Note that we don't currently support Huge pages. On Linux,
* regular data files cannot use Huge pages, and in general
* Huge pages aren't actually pageable. We rely on the OS
* demand-pager to read our data and page it out when memory
* pressure from other processes is high. So until OSs have
* actual paging support for Huge pages, they're not viable.
*/
#define MAX_PAGESIZE (PAGEBASE ? 0x10000 : 0x8000)
/** The minimum number of keys required in a database page.
* Setting this to a larger value will place a smaller bound on the
* maximum size of a data item. Data items larger than this size will
* be pushed into overflow pages instead of being stored directly in
* the B-tree node. This value used to default to 4. With a page size
* of 4096 bytes that meant that any item larger than 1024 bytes would
* go into an overflow page. That also meant that on average 2-3KB of
* each overflow page was wasted space. The value cannot be lower than
* 2 because then there would no longer be a tree structure. With this
* value, items larger than 2KB will go into overflow pages, and on
* average only 1KB will be wasted.
*/
#define MDB_MINKEYS 2
/** A stamp that identifies a file as an LMDB file.
* There's nothing special about this value other than that it is easily
* recognizable, and it will reflect any byte order mismatches.
*/
#define MDB_MAGIC 0xBEEFC0DE
/** The version number for a database's datafile format. */
#define MDB_DATA_VERSION ((MDB_DEVEL) ? 999 : 1)
/** The version number for a database's lockfile format. */
#define MDB_LOCK_VERSION ((MDB_DEVEL) ? 999 : 2)
/** Number of bits representing #MDB_LOCK_VERSION in #MDB_LOCK_FORMAT.
* The remaining bits must leave room for #MDB_lock_desc.
*/
#define MDB_LOCK_VERSION_BITS 12
/** @brief The max size of a key we can write, or 0 for computed max.
*
* This macro should normally be left alone or set to 0.
* Note that a database with big keys or dupsort data cannot be
* reliably modified by a liblmdb which uses a smaller max.
* The default is 511 for backwards compat, or 0 when #MDB_DEVEL.
*
* Other values are allowed, for backwards compat. However:
* A value bigger than the computed max can break if you do not
* know what you are doing, and liblmdb <= 0.9.10 can break when
* modifying a DB with keys/dupsort data bigger than its max.
*
* Data items in an #MDB_DUPSORT database are also limited to
* this size, since they're actually keys of a sub-DB. Keys and
* #MDB_DUPSORT data items must fit on a node in a regular page.
*/
#ifndef MDB_MAXKEYSIZE
#define MDB_MAXKEYSIZE ((MDB_DEVEL) ? 0 : 511)
#endif
/** The maximum size of a key we can write to the environment. */
#if MDB_MAXKEYSIZE
#define ENV_MAXKEY(env) (MDB_MAXKEYSIZE)
#else
#define ENV_MAXKEY(env) ((env)->me_maxkey)
#endif
/** @brief The maximum size of a data item.
*
* We only store a 32 bit value for node sizes.
*/
#define MAXDATASIZE 0xffffffffUL
#if MDB_DEBUG
/** Key size which fits in a #DKBUF.
* @ingroup debug
*/
#define DKBUF_MAXKEYSIZE ((MDB_MAXKEYSIZE) > 0 ? (MDB_MAXKEYSIZE) : 511)
/** A key buffer.
* @ingroup debug
* This is used for printing a hex dump of a key's contents.
*/
#define DKBUF char kbuf[DKBUF_MAXKEYSIZE*2+1]
/** Display a key in hex.
* @ingroup debug
* Invoke a function to display a key in hex.
*/
#define DKEY(x) mdb_dkey(x, kbuf)
#else
#define DKBUF
#define DKEY(x) 0
#endif
/** An invalid page number.
* Mainly used to denote an empty tree.
*/
#define P_INVALID (~(pgno_t)0)
/** Test if the flags \b f are set in a flag word \b w. */
#define F_ISSET(w, f) (((w) & (f)) == (f))
/** Round \b n up to an even number. */
#define EVEN(n) (((n) + 1U) & -2) /* sign-extending -2 to match n+1U */
/** Least significant 1-bit of \b n. n must be of an unsigned type. */
#define LOW_BIT(n) ((n) & (-(n)))
/** (log2(\b p2) % \b n), for p2 = power of 2 and 0 < n < 8. */
#define LOG2_MOD(p2, n) (7 - 86 / ((p2) % ((1U<<(n))-1) + 11))
/* Explanation: Let p2 = 2**(n*y + x), x<n and M = (1U<<n)-1. Now p2 =
* (M+1)**y * 2**x = 2**x (mod M). Finally "/" "happens" to return 7-x.
*/
/** Should be alignment of \b type. Ensure it is a power of 2. */
#define ALIGNOF2(type) \
LOW_BIT(offsetof(struct { char ch_; type align_; }, align_))
/** Used for offsets within a single page.
* Since memory pages are typically 4 or 8KB in size, 12-13 bits,
* this is plenty.
*/
typedef uint16_t indx_t;
typedef unsigned long long mdb_hash_t;
/** Default size of memory map.
* This is certainly too small for any actual applications. Apps should always set
* the size explicitly using #mdb_env_set_mapsize().
*/
#define DEFAULT_MAPSIZE 1048576
/** @defgroup readers Reader Lock Table
* Readers don't acquire any locks for their data access. Instead, they
* simply record their transaction ID in the reader table. The reader
* mutex is needed just to find an empty slot in the reader table. The
* slot's address is saved in thread-specific data so that subsequent read
* transactions started by the same thread need no further locking to proceed.
*
* If #MDB_NOTLS is set, the slot address is not saved in thread-specific data.
*
* No reader table is used if the database is on a read-only filesystem, or
* if #MDB_NOLOCK is set.
*
* Since the database uses multi-version concurrency control, readers don't
* actually need any locking. This table is used to keep track of which
* readers are using data from which old transactions, so that we'll know
* when a particular old transaction is no longer in use. Old transactions
* that have discarded any data pages can then have those pages reclaimed
* for use by a later write transaction.
*
* The lock table is constructed such that reader slots are aligned with the
* processor's cache line size. Any slot is only ever used by one thread.
* This alignment guarantees that there will be no contention or cache
* thrashing as threads update their own slot info, and also eliminates
* any need for locking when accessing a slot.
*
* A writer thread will scan every slot in the table to determine the oldest
* outstanding reader transaction. Any freed pages older than this will be
* reclaimed by the writer. The writer doesn't use any locks when scanning
* this table. This means that there's no guarantee that the writer will
* see the most up-to-date reader info, but that's not required for correct
* operation - all we need is to know the upper bound on the oldest reader,
* we don't care at all about the newest reader. So the only consequence of
* reading stale information here is that old pages might hang around a
* while longer before being reclaimed. That's actually good anyway, because
* the longer we delay reclaiming old pages, the more likely it is that a
* string of contiguous pages can be found after coalescing old pages from
* many old transactions together.
* @{
*/
/** Number of slots in the reader table.
* This value was chosen somewhat arbitrarily. 126 readers plus a
* couple mutexes fit exactly into 8KB on my development machine.
* Applications should set the table size using #mdb_env_set_maxreaders().
*/
#define DEFAULT_READERS 126
/** The size of a CPU cache line in bytes. We want our lock structures
* aligned to this size to avoid false cache line sharing in the
* lock table.
* This value works for most CPUs. For Itanium this should be 128.
*/
#ifndef CACHELINE
#define CACHELINE 64
#endif
/** The information we store in a single slot of the reader table.
* In addition to a transaction ID, we also record the process and
* thread ID that owns a slot, so that we can detect stale information,
* e.g. threads or processes that went away without cleaning up.
* @note We currently don't check for stale records. We simply re-init
* the table when we know that we're the only process opening the
* lock file.
*/
typedef struct MDB_rxbody {
/** Current Transaction ID when this transaction began, or (txnid_t)-1.
* Multiple readers that start at the same time will probably have the
* same ID here. Again, it's not important to exclude them from
* anything; all we need to know is which version of the DB they
* started from so we can avoid overwriting any data used in that
* particular version.
*/
volatile txnid_t mrb_txnid;
/** The process ID of the process owning this reader txn. */
volatile MDB_PID_T mrb_pid;
/** The thread ID of the thread owning this txn. */
volatile MDB_THR_T mrb_tid;
} MDB_rxbody;
/** The actual reader record, with cacheline padding. */
typedef struct MDB_reader {
union {
MDB_rxbody mrx;
/** shorthand for mrb_txnid */
#define mr_txnid mru.mrx.mrb_txnid
#define mr_pid mru.mrx.mrb_pid
#define mr_tid mru.mrx.mrb_tid
/** cache line alignment */
char pad[(sizeof(MDB_rxbody)+CACHELINE-1) & ~(CACHELINE-1)];
} mru;
} MDB_reader;
/** The header for the reader table.
* The table resides in a memory-mapped file. (This is a different file
* than is used for the main database.)
*
* For POSIX the actual mutexes reside in the shared memory of this
* mapped file. On Windows, mutexes are named objects allocated by the
* kernel; we store the mutex names in this mapped file so that other
* processes can grab them. This same approach is also used on
* MacOSX/Darwin (using named semaphores) since MacOSX doesn't support
* process-shared POSIX mutexes. For these cases where a named object
* is used, the object name is derived from a 64 bit FNV hash of the
* environment pathname. As such, naming collisions are extremely
* unlikely. If a collision occurs, the results are unpredictable.
*/
typedef struct MDB_txbody {
/** Stamp identifying this as an LMDB file. It must be set
* to #MDB_MAGIC. */
uint32_t mtb_magic;
/** Format of this lock file. Must be set to #MDB_LOCK_FORMAT. */
uint32_t mtb_format;
/** The ID of the last transaction committed to the database.
* This is recorded here only for convenience; the value can always
* be determined by reading the main database meta pages.
*/
volatile txnid_t mtb_txnid;
/** The number of slots that have been used in the reader table.
* This always records the maximum count, it is not decremented
* when readers release their slots.
*/
volatile unsigned mtb_numreaders;
#if defined(_WIN32) || defined(MDB_USE_POSIX_SEM)
/** Binary form of names of the reader/writer locks */
mdb_hash_t mtb_mutexid;
#elif defined(MDB_USE_SYSV_SEM)
int mtb_semid;
int mtb_rlocked;
#else
/** Mutex protecting access to this table.
* This is the reader table lock used with LOCK_MUTEX().
*/
mdb_mutex_t mtb_rmutex;
#endif
} MDB_txbody;
/** The actual reader table definition. */
typedef struct MDB_txninfo {
union {
MDB_txbody mtb;
#define mti_magic mt1.mtb.mtb_magic
#define mti_format mt1.mtb.mtb_format
#define mti_rmutex mt1.mtb.mtb_rmutex
#define mti_txnid mt1.mtb.mtb_txnid
#define mti_numreaders mt1.mtb.mtb_numreaders
#define mti_mutexid mt1.mtb.mtb_mutexid
#ifdef MDB_USE_SYSV_SEM
#define mti_semid mt1.mtb.mtb_semid
#define mti_rlocked mt1.mtb.mtb_rlocked
#endif
char pad[(sizeof(MDB_txbody)+CACHELINE-1) & ~(CACHELINE-1)];
} mt1;
#if !(defined(_WIN32) || defined(MDB_USE_POSIX_SEM))
union {
#ifdef MDB_USE_SYSV_SEM
int mt2_wlocked;
#define mti_wlocked mt2.mt2_wlocked
#else
mdb_mutex_t mt2_wmutex;
#define mti_wmutex mt2.mt2_wmutex
#endif
char pad[(MNAME_LEN+CACHELINE-1) & ~(CACHELINE-1)];
} mt2;
#endif
MDB_reader mti_readers[1];
} MDB_txninfo;
/** Lockfile format signature: version, features and field layout */
#define MDB_LOCK_FORMAT \
((uint32_t) \
(((MDB_LOCK_VERSION) % (1U << MDB_LOCK_VERSION_BITS)) \
+ MDB_lock_desc * (1U << MDB_LOCK_VERSION_BITS)))
/** Lock type and layout. Values 0-119. _WIN32 implies #MDB_PIDLOCK.
* Some low values are reserved for future tweaks.
*/
#ifdef _WIN32
# define MDB_LOCK_TYPE (0 + ALIGNOF2(mdb_hash_t)/8 % 2)
#elif defined MDB_USE_POSIX_SEM
# define MDB_LOCK_TYPE (4 + ALIGNOF2(mdb_hash_t)/8 % 2)
#elif defined MDB_USE_SYSV_SEM
# define MDB_LOCK_TYPE (8)
#elif defined MDB_USE_POSIX_MUTEX
/* We do not know the inside of a POSIX mutex and how to check if mutexes
* used by two executables are compatible. Just check alignment and size.
*/
# define MDB_LOCK_TYPE (10 + \
LOG2_MOD(ALIGNOF2(pthread_mutex_t), 5) + \
sizeof(pthread_mutex_t) / 4U % 22 * 5)
#endif
enum {
/** Magic number for lockfile layout and features.
*
* This *attempts* to stop liblmdb variants compiled with conflicting
* options from using the lockfile at the same time and thus breaking
* it. It describes locking types, and sizes and sometimes alignment
* of the various lockfile items.
*
* The detected ranges are mostly guesswork, or based simply on how
* big they could be without using more bits. So we can tweak them
* in good conscience when updating #MDB_LOCK_VERSION.
*/
MDB_lock_desc =
/* Default CACHELINE=64 vs. other values (have seen mention of 32-256) */
(CACHELINE==64 ? 0 : 1 + LOG2_MOD(CACHELINE >> (CACHELINE>64), 5))
+ 6 * (sizeof(MDB_PID_T)/4 % 3) /* legacy(2) to word(4/8)? */
+ 18 * (sizeof(pthread_t)/4 % 5) /* can be struct{id, active data} */
+ 90 * (sizeof(MDB_txbody) / CACHELINE % 3)
+ 270 * (MDB_LOCK_TYPE % 120)
/* The above is < 270*120 < 2**15 */
+ ((sizeof(txnid_t) == 8) << 15) /* 32bit/64bit */
+ ((sizeof(MDB_reader) > CACHELINE) << 16)
/* Not really needed - implied by MDB_LOCK_TYPE != (_WIN32 locking) */
+ (((MDB_PIDLOCK) != 0) << 17)
/* 18 bits total: Must be <= (32 - MDB_LOCK_VERSION_BITS). */
};
/** @} */
/** Common header for all page types. The page type depends on #mp_flags.
*
* #P_BRANCH and #P_LEAF pages have unsorted '#MDB_node's at the end, with
* sorted #mp_ptrs[] entries referring to them. Exception: #P_LEAF2 pages
* omit mp_ptrs and pack sorted #MDB_DUPFIXED values after the page header.
*
* #P_OVERFLOW records occupy one or more contiguous pages where only the
* first has a page header. They hold the real data of #F_BIGDATA nodes.
*
* #P_SUBP sub-pages are small leaf "pages" with duplicate data.
* A node with flag #F_DUPDATA but not #F_SUBDATA contains a sub-page.
* (Duplicate data can also go in sub-databases, which use normal pages.)
*
* #P_META pages contain #MDB_meta, the start point of an LMDB snapshot.
*
* Each non-metapage up to #MDB_meta.%mm_last_pg is reachable exactly once
* in the snapshot: Either used by a database or listed in a freeDB record.
*/
typedef struct MDB_page {
#define mp_pgno mp_p.p_pgno
#define mp_next mp_p.p_next
union {
pgno_t p_pgno; /**< page number */
struct MDB_page *p_next; /**< for in-memory list of freed pages */
} mp_p;
uint16_t mp_pad; /**< key size if this is a LEAF2 page */
/** @defgroup mdb_page Page Flags
* @ingroup internal
* Flags for the page headers.
* @{
*/
#define P_BRANCH 0x01 /**< branch page */
#define P_LEAF 0x02 /**< leaf page */
#define P_OVERFLOW 0x04 /**< overflow page */
#define P_META 0x08 /**< meta page */
#define P_DIRTY 0x10 /**< dirty page, also set for #P_SUBP pages */
#define P_LEAF2 0x20 /**< for #MDB_DUPFIXED records */
#define P_SUBP 0x40 /**< for #MDB_DUPSORT sub-pages */
#define P_LOOSE 0x4000 /**< page was dirtied then freed, can be reused */
#define P_KEEP 0x8000 /**< leave this page alone during spill */
/** @} */
uint16_t mp_flags; /**< @ref mdb_page */