Add MDB_NOMETASYNC env option.

Just a trial. This may not make sense if we decide to split the
meta pages into their own separate file, to allow meta traffic to
reside on a separate spindle.

diff --git a/libraries/libmdb/mdb.c b/libraries/libmdb/mdb.c
index 729725dd928ba7aa5962a082bd6102632b19320b..c32057c8a175c25a3f069038754ecd2f285f49de 100644 (file)
--- a/libraries/libmdb/mdb.c
+++ b/libraries/libmdb/mdb.c
@@ -3037,7 +3037,7 @@ mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode)
        }
 
        if ((rc = mdb_env_open2(env, flags)) == MDB_SUCCESS) {
-               if (flags & (MDB_RDONLY|MDB_NOSYNC)) {
+               if (flags & (MDB_RDONLY|MDB_NOSYNC|MDB_NOMETASYNC)) {
                        env->me_mfd = env->me_fd;
                } else {
                        /* synchronous fd for meta writes */
@@ -6096,7 +6096,7 @@ mdb_put(MDB_txn *txn, MDB_dbi dbi,
  *     at runtime. Changing other flags requires closing the environment
  *     and re-opening it with the new flags.
  */
-#define        CHANGEABLE      (MDB_NOSYNC)
+#define        CHANGEABLE      (MDB_NOSYNC|MDB_NOMETASYNC)
 int
 mdb_env_set_flags(MDB_env *env, unsigned int flag, int onoff)
 {

diff --git a/libraries/libmdb/mdb.h b/libraries/libmdb/mdb.h
index bcf36659c4a632d3ecfbbf1430484a795299e32f..587013f6f4c7de819b550732c2a7a85e01e95b89 100644 (file)
--- a/libraries/libmdb/mdb.h
+++ b/libraries/libmdb/mdb.h
@@ -159,6 +159,8 @@ typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *rel
 #define MDB_NOSYNC             0x10000
        /** read only */
 #define MDB_RDONLY             0x20000
+       /** don't fsync metapage after commit */
+#define MDB_NOMETASYNC         0x40000
 /** @} */
 
 /**    @defgroup       mdb_open        Database Flags
@@ -334,6 +336,13 @@ int  mdb_env_create(MDB_env **env);
         *              at risk is governed by how often the system flushes dirty buffers to disk
         *              and how often #mdb_env_sync() is called. This flag may be changed
         *              at any time using #mdb_env_set_flags().
+        *      <li>#MDB_NOMETASYNC
+        *              Don't perform a synchronous flush of the meta page after committing
+        *              a transaction. This is similar to the #MDB_NOSYNC case, but safer
+        *              because the transaction data is still flushed. The meta page for any
+        *              transaction N will be flushed by the data flush of transaction N+1.
+        *              In case of a system crash, the last committed transaction may be
+        *              lost. This flag may be changed at any time using #mdb_env_set_flags().
         *      <li>#MDB_RDONLY
         *              Open the environment in read-only mode. No write operations will be allowed.
         * </ul>
@@ -392,8 +401,7 @@ void mdb_env_close(MDB_env *env);
        /** @brief Set environment flags.
         *
         * This may be used to set some flags that weren't already set during
-        * #mdb_env_open(), or to unset these flags. Currently only the
-        * #MDB_NOSYNC flag setting may be changed with this function.
+        * #mdb_env_open(), or to unset these flags.
         * @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.