diff --git a/libraries/liblmdb/lmdb.h b/libraries/liblmdb/lmdb.h
index 9e51b55..1f4736c 100644
--- a/libraries/liblmdb/lmdb.h
+++ b/libraries/liblmdb/lmdb.h
@@ -332,8 +332,8 @@ typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *rel
#define MDB_NORDAHEAD 0x800000
/** don't initialize malloc'd memory before writing to datafile */
#define MDB_NOMEMINIT 0x1000000
- /** use the previous meta page rather than the latest one */
-#define MDB_PREVMETA 0x2000000
+ /** use the previous snapshot rather than the latest one */
+#define MDB_PREVSNAPSHOT 0x2000000
/** @} */
/** @defgroup mdb_dbi_open Database Flags
@@ -648,10 +648,12 @@ int mdb_env_create(MDB_env **env);
* 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().
- * #MDB_PREVMETA
- * Open the environment with the previous meta page rather than the latest
+ * #MDB_PREVSNAPSHOT
+ * Open the environment with the previous snapshot rather than the latest
* one. This loses the latest transaction, but may help work around some
- * types of corruption.
+ * types of corruption. If opened with write access, this must be the
+ * only process using the environment. This flag is automatically reset
+ * after a write transaction is successfully committed.
*
* @param[in] mode The UNIX permissions to set on created files and semaphores.
* This parameter is ignored on Windows.
diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 433fe50..fb57a72 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -3793,6 +3793,8 @@ done:
return MDB_SUCCESS;
}
+static int ESECT mdb_env_share_locks(MDB_env *env, int *excl);
+
int
mdb_txn_commit(MDB_txn *txn)
{
@@ -4015,6 +4017,15 @@ mdb_txn_commit(MDB_txn *txn)
if ((rc = mdb_env_write_meta(txn)))
goto fail;
end_mode = MDB_END_COMMITTED|MDB_END_UPDATE;
+ if (env->me_flags & MDB_PREVSNAPSHOT) {
+ if (!(env->me_flags & MDB_NOLOCK)) {
+ int excl;
+ rc = mdb_env_share_locks(env, &excl);
+ if (rc)
+ goto fail;
+ }
+ env->me_flags ^= MDB_PREVSNAPSHOT;
+ }
done:
mdb_txn_end(txn, end_mode);
@@ -4296,7 +4307,8 @@ static MDB_meta *
mdb_env_pick_meta(const MDB_env *env)
{
MDB_meta *const *metas = env->me_metas;
- return metas[ metas[0]->mm_txnid < metas[1]->mm_txnid ];
+ return metas[ (metas[0]->mm_txnid < metas[1]->mm_txnid) ^
+ ((env->me_flags & MDB_PREVSNAPSHOT) != 0) ];
}
int ESECT
@@ -4868,6 +4880,9 @@ mdb_env_open2(MDB_env *env, int prev)
#endif
env->me_maxpg = env->me_mapsize / env->me_psize;
+ if (env->me_txns)
+ env->me_txns->mti_txnid = meta.mm_txnid;
+
#if MDB_DEBUG
{
MDB_meta *meta = mdb_env_pick_meta(env);
@@ -4967,9 +4982,6 @@ static int ESECT
mdb_env_share_locks(MDB_env *env, int *excl)
{
int rc = 0;
- MDB_meta *meta = mdb_env_pick_meta(env);
-
- env->me_txns->mti_txnid = meta->mm_txnid;
#ifdef _WIN32
{
@@ -5391,7 +5403,7 @@ fail:
*/
#define CHANGEABLE (MDB_NOSYNC|MDB_NOMETASYNC|MDB_MAPASYNC|MDB_NOMEMINIT)
#define CHANGELESS (MDB_FIXEDMAP|MDB_NOSUBDIR|MDB_RDONLY| \
- MDB_WRITEMAP|MDB_NOTLS|MDB_NOLOCK|MDB_NORDAHEAD|MDB_PREVMETA)
+ MDB_WRITEMAP|MDB_NOTLS|MDB_NOLOCK|MDB_NORDAHEAD|MDB_PREVSNAPSHOT)
#if VALID_FLAGS & PERSISTENT_FLAGS & (CHANGEABLE|CHANGELESS)
# error "Persistent DB flags & env flags overlap, but both go in mm_flags"
@@ -5477,6 +5489,10 @@ mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode
rc = mdb_env_setup_locks(env, &fname, mode, &excl);
if (rc)
goto leave;
+ if ((flags & MDB_PREVSNAPSHOT) && !excl) {
+ rc = EAGAIN;
+ goto leave;
+ }
}
rc = mdb_fopen(env, &fname,
@@ -5491,7 +5507,7 @@ mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode
goto leave;
}
- if ((rc = mdb_env_open2(env, flags & MDB_PREVMETA)) == MDB_SUCCESS) {
+ if ((rc = mdb_env_open2(env, flags & MDB_PREVSNAPSHOT)) == MDB_SUCCESS) {
if (!(flags & (MDB_RDONLY|MDB_WRITEMAP))) {
/* Synchronous fd for meta writes. Needed even with
* MDB_NOSYNC/MDB_NOMETASYNC, in case these get reset.
@@ -5501,7 +5517,7 @@ mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode
goto leave;
}
DPRINTF(("opened dbenv %p", (void *) env));
- if (excl > 0) {
+ if (excl > 0 && !(flags & MDB_PREVSNAPSHOT)) {
rc = mdb_env_share_locks(env, &excl);
if (rc)
goto leave;
diff --git a/libraries/liblmdb/mdb_copy.c b/libraries/liblmdb/mdb_copy.c
index 98df57a..23be815 100644
--- a/libraries/liblmdb/mdb_copy.c
+++ b/libraries/liblmdb/mdb_copy.c
@@ -39,7 +39,7 @@ int main(int argc,char * argv[])
if (argv[1][1] == 'n' && argv[1][2] == '\0')
flags |= MDB_NOSUBDIR;
else if (argv[1][1] == 'v' && argv[1][2] == '\0')
- flags |= MDB_PREVMETA;
+ flags |= MDB_PREVSNAPSHOT;
else if (argv[1][1] == 'c' && argv[1][2] == '\0')
cpflags |= MDB_CP_COMPACT;
else if (argv[1][1] == 'V' && argv[1][2] == '\0') {
diff --git a/libraries/liblmdb/mdb_dump.c b/libraries/liblmdb/mdb_dump.c
index 8ba688d..b7737f1 100644
--- a/libraries/liblmdb/mdb_dump.c
+++ b/libraries/liblmdb/mdb_dump.c
@@ -175,7 +175,7 @@ int main(int argc, char *argv[])
* -n: use NOSUBDIR flag on env_open
* -p: use printable characters
* -f: write to file instead of stdout
- * -v: use previous metapage
+ * -v: use previous snapshot
* -V: print version and exit
* (default) dump only the main DB
*/
@@ -204,7 +204,7 @@ int main(int argc, char *argv[])
envflags |= MDB_NOSUBDIR;
break;
case 'v':
- envflags |= MDB_PREVMETA;
+ envflags |= MDB_PREVSNAPSHOT;
break;
case 'p':
mode |= PRINT;
diff --git a/libraries/liblmdb/mdb_stat.c b/libraries/liblmdb/mdb_stat.c
index 1ec1042..08f30be 100644
--- a/libraries/liblmdb/mdb_stat.c
+++ b/libraries/liblmdb/mdb_stat.c
@@ -61,7 +61,7 @@ int main(int argc, char *argv[])
* -f: print freelist info
* -r: print reader info
* -n: use NOSUBDIR flag on env_open
- * -v: use previous metapage
+ * -v: use previous snapshot
* -V: print version and exit
* (default) print stat of only the main DB
*/
@@ -86,7 +86,7 @@ int main(int argc, char *argv[])
envflags |= MDB_NOSUBDIR;
break;
case 'v':
- envflags |= MDB_PREVMETA;
+ envflags |= MDB_PREVSNAPSHOT;
break;
case 'r':
rdrinfo++;