Support MDB_NOSYNC on mdb_txn_begin()

libraries/liblmdb/lmdb.h

@@ -930,6 +930,8 @@ int  mdb_env_set_assert(MDB_env *env, MDB_assert_func *func);
 	 * <ul>
 	 *	<li>#MDB_RDONLY
 	 *		This transaction will not perform any write operations.
+	 *	<li>#MDB_NOSYNC
+	 *		Don't flush system buffers to disk when committing this transaction.
 	 * </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

libraries/liblmdb/mdb.c

@@ -1084,6 +1084,7 @@ struct MDB_txn {
 #define MDB_TXN_ERROR		0x02		/**< txn is unusable after an error */
 #define MDB_TXN_DIRTY		0x04		/**< must write, even if dirty list is empty */
 #define MDB_TXN_SPILLS		0x08		/**< txn or a parent has spilled pages */
+#define MDB_TXN_NOSYNC		0x10		/**< don't sync this txn on commit */
 /** @} */
 	unsigned int	mt_flags;		/**< @ref mdb_txn */
 	/** #dirty_list room: Array size - \#dirty pages visible to this txn.
@@ -2755,6 +2756,8 @@ mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
 		txn->mt_dbflags = (unsigned char *)(txn->mt_dbs + env->me_maxdbs);
 		txn->mt_dbiseqs = env->me_dbiseqs;
 	} else {
+		if (flags & MDB_NOSYNC)
+			txn->mt_flags |= MDB_TXN_NOSYNC;
 		txn->mt_cursors = (MDB_cursor **)(txn->mt_dbs + env->me_maxdbs);
 		if (parent) {
 			txn->mt_dbiseqs = parent->mt_dbiseqs;
@@ -3486,9 +3489,12 @@ mdb_txn_commit(MDB_txn *txn)
 	mdb_audit(txn);
 #endif
 
-	if ((rc = mdb_page_flush(txn, 0)) ||
-		(rc = mdb_env_sync(env, 0)) ||
-		(rc = mdb_env_write_meta(txn)))
+	if ((rc = mdb_page_flush(txn, 0)))
+		goto fail;
+	if (!F_ISSET(txn->mt_flags, MDB_TXN_NOSYNC) &&
+		(rc = mdb_env_sync(env, 0)))
+		goto fail;
+	if ((rc = mdb_env_write_meta(txn)))
 		goto fail;
 
 	/* Free P_LOOSE pages left behind in dirty_list */
@@ -3682,6 +3688,8 @@ mdb_env_write_meta(MDB_txn *txn)
 		__sync_synchronize();
 #endif
 		mp->mm_txnid = txn->mt_txnid;
+		if (F_ISSET(txn->mt_flags, MDB_TXN_NOSYNC))
+			goto done;
 		if (!(env->me_flags & (MDB_NOMETASYNC|MDB_NOSYNC))) {
 			unsigned meta_size = env->me_psize;
 			rc = (env->me_flags & MDB_MAPASYNC) ? MS_ASYNC : MS_SYNC;
@@ -3718,7 +3726,8 @@ mdb_env_write_meta(MDB_txn *txn)
 	off += PAGEHDRSZ;
 
 	/* Write to the SYNC fd */
-	mfd = env->me_flags & (MDB_NOSYNC|MDB_NOMETASYNC) ?
+	mfd = ((env->me_flags & (MDB_NOSYNC|MDB_NOMETASYNC)) ||
+		(txn->mt_flags & MDB_TXN_NOSYNC)) ?
 		env->me_fd : env->me_mfd;
 #ifdef _WIN32
 	{