Import from SAMBA's tdb:

commit b90863c0b7b860b006ac49c9396711ff351f777f
Author: Howard Chu <hyc@highlandsun.com>
Date:   Tue Mar 31 13:15:54 2009 +1100

    Add tdb_transaction_prepare_commit()
    
    Using tdb_transaction_prepare_commit() gives us 2-phase commits. This
    allows us to safely commit across multiple tdb databases at once, with
    reasonable transaction semantics
    
    Signed-off-by: tridge@samba.org

ccan/tdb/tdb.c

@@ -898,6 +898,16 @@ void tdb_trace(struct tdb_context *tdb, const char *op)
 	tdb_trace_end(tdb);
 }
 
+void tdb_trace_seqnum(struct tdb_context *tdb, uint32_t seqnum, const char *op)
+{
+	char msg[sizeof(tdb_off_t) * 4];
+
+	sprintf(msg, "%u ", seqnum);
+	tdb_trace_write(tdb, msg);
+	tdb_trace_write(tdb, op);
+	tdb_trace_end(tdb);
+}
+
 void tdb_trace_open(struct tdb_context *tdb, const char *op,
 		    unsigned hash_size, unsigned tdb_flags, unsigned open_flags)
 {

ccan/tdb/tdb.h

@@ -137,6 +137,7 @@ int tdb_fd(struct tdb_context *tdb);
 tdb_log_func tdb_log_fn(struct tdb_context *tdb);
 void *tdb_get_logging_private(struct tdb_context *tdb);
 int tdb_transaction_start(struct tdb_context *tdb);
+int tdb_transaction_prepare_commit(struct tdb_context *tdb);
 int tdb_transaction_commit(struct tdb_context *tdb);
 int tdb_transaction_cancel(struct tdb_context *tdb);
 int tdb_transaction_recover(struct tdb_context *tdb);

ccan/tdb/tdb_private.h

@@ -49,7 +49,7 @@
 #endif
 #include "tdb.h"
 
-/* #define TDB_TRACE 1 */
+#define TDB_TRACE 1
 
 #if HAVE_GETPAGESIZE
 #define getpagesize() 0x2000
@@ -90,6 +90,7 @@ typedef uint32_t tdb_off_t;
 
 #ifdef TDB_TRACE
 void tdb_trace(struct tdb_context *tdb, const char *op);
+void tdb_trace_seqnum(struct tdb_context *tdb, uint32_t seqnum, const char *op);
 void tdb_trace_open(struct tdb_context *tdb, const char *op,
 		    unsigned hash_size, unsigned tdb_flags, unsigned open_flags);
 void tdb_trace_ret(struct tdb_context *tdb, const char *op, int ret);
@@ -107,6 +108,7 @@ void tdb_trace_2rec_retrec(struct tdb_context *tdb, const char *op,
 			   TDB_DATA rec1, TDB_DATA rec2, TDB_DATA ret);
 #else
 #define tdb_trace(tdb, op)
+#define tdb_trace_seqnum(tdb, seqnum, op)
 #define tdb_trace_open(tdb, op, hash_size, tdb_flags, open_flags)
 #define tdb_trace_ret(tdb, op, ret)
 #define tdb_trace_retrec(tdb, op, ret)
@@ -216,7 +218,10 @@ struct tdb_context {
 	int page_size;
 	int max_dead_records;
 	int transaction_lock_count;
+#ifdef TDB_TRACE
 	int tracefd;
+	uint32_t transaction_prepare_seqnum;
+#endif
 	volatile sig_atomic_t *interrupt_sig_ptr;
 };
 

ccan/tdb/tools/keywords.c

@@ -38,7 +38,7 @@ struct op_table {
 	void (*enhance_op)(const char *filename,
 			   struct op op[], unsigned int op_num, char *words[]);
 };
-/* maximum key range = 43, duplicates = 0 */
+/* maximum key range = 48, duplicates = 0 */
 
 #ifdef __GNUC__
 __inline
@@ -52,32 +52,32 @@ hash_keyword (register const char *str, register unsigned int len)
 {
   static const unsigned char asso_values[] =
     {
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 20, 51, 25,
-       5,  0,  0,  5,  5, 51, 51,  0,  0,  0,
-      20, 51, 20, 51, 51,  0,  5,  0, 51,  0,
-      51,  5, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51, 51, 51, 51, 51,
-      51, 51, 51, 51, 51, 51
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 20, 56, 30,
+       5,  0,  0,  5,  5, 56, 56,  0,  0,  0,
+      20, 56, 20, 56, 56,  0,  5,  0, 56,  0,
+      56,  5, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56, 56, 56, 56, 56,
+      56, 56, 56, 56, 56, 56
     };
   return len + asso_values[(unsigned char)str[4]] + asso_values[(unsigned char)str[len - 1]];
 }
@@ -93,17 +93,17 @@ find_keyword (register const char *str, register unsigned int len)
 {
   enum
     {
-      TOTAL_KEYWORDS = 33,
+      TOTAL_KEYWORDS = 34,
       MIN_WORD_LENGTH = 8,
-      MAX_WORD_LENGTH = 25,
+      MAX_WORD_LENGTH = 30,
       MIN_HASH_VALUE = 8,
-      MAX_HASH_VALUE = 50
+      MAX_HASH_VALUE = 55
     };
 
   static const struct op_table wordlist[] =
     {
       {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
-#line 43 "keywords.gperf"
+#line 44 "keywords.gperf"
       {"traverse", OP_TDB_TRAVERSE, op_add_traverse,},
 #line 33 "keywords.gperf"
       {"tdb_store", OP_TDB_STORE, op_add_store,},
@@ -115,13 +115,13 @@ find_keyword (register const char *str, register unsigned int len)
       {"tdb_wipe_all", OP_TDB_WIPE_ALL, op_add_nothing,},
 #line 20 "keywords.gperf"
       {"tdb_unlockall", OP_TDB_UNLOCKALL, op_add_nothing,},
-#line 47 "keywords.gperf"
-      {"tdb_fetch", OP_TDB_FETCH, op_add_key_data,},
 #line 48 "keywords.gperf"
+      {"tdb_fetch", OP_TDB_FETCH, op_add_key_data,},
+#line 49 "keywords.gperf"
       {"tdb_delete", OP_TDB_DELETE, op_add_key_ret,},
 #line 17 "keywords.gperf"
       {"tdb_lockall_mark", OP_TDB_LOCKALL_MARK, op_add_nothing,},
-#line 45 "keywords.gperf"
+#line 46 "keywords.gperf"
       {"tdb_firstkey", OP_TDB_FIRSTKEY, op_add_key,},
 #line 18 "keywords.gperf"
       {"tdb_lockall_unmark", OP_TDB_LOCKALL_UNMARK, op_add_nothing,},
@@ -137,35 +137,38 @@ find_keyword (register const char *str, register unsigned int len)
       {""},
 #line 22 "keywords.gperf"
       {"tdb_lockall_read_nonblock", OP_TDB_LOCKALL_READ_NONBLOCK, op_add_nothing,},
-#line 42 "keywords.gperf"
+#line 43 "keywords.gperf"
       {"tdb_traverse_end", OP_TDB_TRAVERSE_END, op_analyze_traverse,},
 #line 38 "keywords.gperf"
       {"tdb_transaction_cancel", OP_TDB_TRANSACTION_CANCEL, op_analyze_transaction,},
-#line 41 "keywords.gperf"
+#line 42 "keywords.gperf"
       {"tdb_traverse_start", OP_TDB_TRAVERSE_START, op_add_traverse_start,},
       {""},
-#line 44 "keywords.gperf"
+#line 45 "keywords.gperf"
       {"traversefn", OP_TDB_TRAVERSE, op_add_traversefn,},
 #line 37 "keywords.gperf"
       {"tdb_transaction_start", OP_TDB_TRANSACTION_START, op_add_transaction,},
 #line 39 "keywords.gperf"
       {"tdb_transaction_commit", OP_TDB_TRANSACTION_COMMIT, op_analyze_transaction,},
-#line 40 "keywords.gperf"
+#line 41 "keywords.gperf"
       {"tdb_traverse_read_start", OP_TDB_TRAVERSE_READ_START, op_add_traverse_start,},
       {""},
 #line 34 "keywords.gperf"
       {"tdb_append", OP_TDB_APPEND, op_add_append,},
-#line 46 "keywords.gperf"
+#line 47 "keywords.gperf"
       {"tdb_nextkey", OP_TDB_NEXTKEY, op_add_key_data,},
+      {""}, {""}, {""},
+#line 40 "keywords.gperf"
+      {"tdb_transaction_prepare_commit", OP_TDB_TRANSACTION_PREPARE_COMMIT, op_add_nothing,},
+#line 31 "keywords.gperf"
+      {"tdb_parse_record", OP_TDB_PARSE_RECORD, op_add_key_ret,},
       {""},
 #line 24 "keywords.gperf"
       {"tdb_chainlock", OP_TDB_CHAINLOCK, op_add_chainlock,},
       {""},
 #line 28 "keywords.gperf"
       {"tdb_chainunlock", OP_TDB_CHAINUNLOCK, op_analyze_chainlock,},
-#line 31 "keywords.gperf"
-      {"tdb_parse_record", OP_TDB_PARSE_RECORD, op_add_key_ret,},
-      {""},
+      {""}, {""},
 #line 26 "keywords.gperf"
       {"tdb_chainlock_mark", OP_TDB_CHAINLOCK_MARK, op_add_key,},
       {""},

ccan/tdb/tools/keywords.gperf

@@ -37,6 +37,7 @@ tdb_wipe_all, OP_TDB_WIPE_ALL, op_add_nothing,
 tdb_transaction_start, OP_TDB_TRANSACTION_START, op_add_transaction,
 tdb_transaction_cancel, OP_TDB_TRANSACTION_CANCEL, op_analyze_transaction,
 tdb_transaction_commit, OP_TDB_TRANSACTION_COMMIT, op_analyze_transaction,
+tdb_transaction_prepare_commit, OP_TDB_TRANSACTION_PREPARE_COMMIT, op_add_nothing,
 tdb_traverse_read_start, OP_TDB_TRAVERSE_READ_START, op_add_traverse_start,
 tdb_traverse_start, OP_TDB_TRAVERSE_START, op_add_traverse_start,
 tdb_traverse_end, OP_TDB_TRAVERSE_END, op_analyze_traverse,

ccan/tdb/tools/replay_trace.c

@@ -116,6 +116,7 @@ enum op_type {
 	OP_TDB_WIPE_ALL,
 	OP_TDB_TRANSACTION_START,
 	OP_TDB_TRANSACTION_CANCEL,
+	OP_TDB_TRANSACTION_PREPARE_COMMIT,
 	OP_TDB_TRANSACTION_COMMIT,
 	OP_TDB_TRAVERSE_READ_START,
 	OP_TDB_TRAVERSE_START,
@@ -764,6 +765,10 @@ unsigned run_ops(struct tdb_context *tdb,
 		case OP_TDB_TRANSACTION_CANCEL:
 			try(tdb_transaction_cancel(tdb), op[file][i].ret);
 			break;
+		case OP_TDB_TRANSACTION_PREPARE_COMMIT:
+			try(tdb_transaction_prepare_commit(tdb),
+			    op[file][i].ret);
+			break;
 		case OP_TDB_TRANSACTION_COMMIT:
 			try(tdb_transaction_commit(tdb), op[file][i].ret);
 			break;

ccan/tdb/tools/tdbtorture.c

@@ -129,13 +129,11 @@ static void addrec_db(void)
 		goto next;
 	}
 	if (in_traverse == 0 && in_transaction && random() % TRANSACTION_PROB == 0) {
-#if 0
 		if (random() % TRANSACTION_PREPARE_PROB == 0) {
 			if (tdb_transaction_prepare_commit(db) != 0) {
 				fatal("tdb_transaction_prepare_commit failed");
 			}
 		}
-#endif
 		if (tdb_transaction_commit(db) != 0) {
 			fatal("tdb_transaction_commit failed");
 		}

ccan/tdb/transaction.c

@@ -121,6 +121,10 @@ struct tdb_transaction {
 	   but don't create a new transaction */
 	int nesting;
 
+	/* set when a prepare has already occurred */
+	bool prepared;
+	tdb_off_t magic_offset;
+
 	/* old file size before transaction */
 	tdb_len_t old_map_size;
 };
@@ -135,6 +139,14 @@ static int transaction_read(struct tdb_context *tdb, tdb_off_t off, void *buf,
 {
 	uint32_t blk;
 
+	/* Only a commit is allowed on a prepared transaction */
+	if (tdb->transaction->prepared) {
+		tdb->ecode = TDB_ERR_EINVAL;
+		TDB_LOG((tdb, TDB_DEBUG_FATAL, "transaction_read: transaction already prepared, read not allowed\n"));
+		tdb->transaction->transaction_error = 1;
+		return -1;
+	}
+
 	/* break it down into block sized ops */
 	while (len + (off % tdb->transaction->block_size) > tdb->transaction->block_size) {
 		tdb_len_t len2 = tdb->transaction->block_size - (off % tdb->transaction->block_size);
@@ -192,6 +204,14 @@ static int transaction_write(struct tdb_context *tdb, tdb_off_t off,
 {
 	uint32_t blk;
 
+	/* Only a commit is allowed on a prepared transaction */
+	if (tdb->transaction->prepared) {
+		tdb->ecode = TDB_ERR_EINVAL;
+		TDB_LOG((tdb, TDB_DEBUG_FATAL, "transaction_write: transaction already prepared, write not allowed\n"));
+		tdb->transaction->transaction_error = 1;
+		return -1;
+	}
+
 	/* if the write is to a hash head, then update the transaction
 	   hash heads */
 	if (len == sizeof(tdb_off_t) && off >= FREELIST_TOP &&
@@ -398,9 +418,34 @@ static const struct tdb_methods transaction_methods = {
 	transaction_brlock
 };
 
+/*
+  sync to disk
+*/
+static int transaction_sync(struct tdb_context *tdb, tdb_off_t offset, tdb_len_t length)
+{	
+	if (fsync(tdb->fd) != 0) {
+		tdb->ecode = TDB_ERR_IO;
+		TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: fsync failed\n"));
+		return -1;
+	}
+#ifdef MS_SYNC
+	if (tdb->map_ptr) {
+		tdb_off_t moffset = offset & ~(tdb->page_size-1);
+		if (msync(moffset + (char *)tdb->map_ptr, 
+			  length + (offset - moffset), MS_SYNC) != 0) {
+			tdb->ecode = TDB_ERR_IO;
+			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: msync failed - %s\n",
+				 strerror(errno)));
+			return -1;
+		}
+	}
+#endif
+	return 0;
+}
+
 int tdb_transaction_cancel_internal(struct tdb_context *tdb)
 {
-	int i;
+	int i, ret = 0;
 
 	if (tdb->transaction == NULL) {
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_cancel: no transaction\n"));
@@ -423,6 +468,18 @@ int tdb_transaction_cancel_internal(struct tdb_context *tdb)
 	}
 	SAFE_FREE(tdb->transaction->blocks);
 
+	if (tdb->transaction->magic_offset) {
+		const struct tdb_methods *methods = tdb->transaction->io_methods;
+		uint32_t zero = 0;
+
+		/* remove the recovery marker */
+		if (methods->tdb_write(tdb, tdb->transaction->magic_offset, &zero, 4) == -1 ||
+		transaction_sync(tdb, tdb->transaction->magic_offset, 4) == -1) {
+			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_cancel: failed to remove recovery magic\n"));
+			ret = -1;
+		}
+	}
+
 	/* remove any global lock created during the transaction */
 	if (tdb->global_lock.count != 0) {
 		tdb_brlock(tdb, FREELIST_TOP, F_UNLCK, F_SETLKW, 0, 4*tdb->header.hash_size);
@@ -448,7 +505,7 @@ int tdb_transaction_cancel_internal(struct tdb_context *tdb)
 	SAFE_FREE(tdb->transaction->hash_heads);
 	SAFE_FREE(tdb->transaction);
 	
-	return 0;
+	return ret;
 }
 
 /*
@@ -570,31 +627,6 @@ int tdb_transaction_cancel(struct tdb_context *tdb)
 	tdb_trace(tdb, "tdb_transaction_cancel");
 	return tdb_transaction_cancel_internal(tdb);
 }
-/*
-  sync to disk
-*/
-static int transaction_sync(struct tdb_context *tdb, tdb_off_t offset, tdb_len_t length)
-{	
-	if (fsync(tdb->fd) != 0) {
-		tdb->ecode = TDB_ERR_IO;
-		TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: fsync failed\n"));
-		return -1;
-	}
-#ifdef MS_SYNC
-	if (tdb->map_ptr) {
-		tdb_off_t moffset = offset & ~(tdb->page_size-1);
-		if (msync(moffset + (char *)tdb->map_ptr, 
-			  length + (offset - moffset), MS_SYNC) != 0) {
-			tdb->ecode = TDB_ERR_IO;
-			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: msync failed - %s\n",
-				 strerror(errno)));
-			return -1;
-		}
-	}
-#endif
-	return 0;
-}
-
 
 /*
   work out how much space the linearised recovery data will consume
@@ -842,26 +874,26 @@ static int transaction_setup_recovery(struct tdb_context *tdb,
 	return 0;
 }
 
-/*
-  commit the current transaction
-*/
-int tdb_transaction_commit(struct tdb_context *tdb)
+static int tdb_transaction_prepare_commit_internal(struct tdb_context *tdb)
 {	
 	const struct tdb_methods *methods;
-	tdb_off_t magic_offset = 0;
-	uint32_t zero = 0;
-	int i;
 
-	tdb_trace(tdb, "tdb_transaction_commit");
 	if (tdb->transaction == NULL) {
-		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: no transaction\n"));
+		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: no transaction\n"));
+		return -1;
+	}
+
+	if (tdb->transaction->prepared) {
+		tdb->ecode = TDB_ERR_EINVAL;
+		tdb_transaction_cancel(tdb);
+		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: transaction already prepared\n"));
 		return -1;
 	}
 
 	if (tdb->transaction->transaction_error) {
 		tdb->ecode = TDB_ERR_IO;
 		tdb_transaction_cancel_internal(tdb);
-		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: transaction error pending\n"));
+		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: transaction error pending\n"));
 		return -1;
 	}
 
@@ -871,9 +903,13 @@ int tdb_transaction_commit(struct tdb_context *tdb)
 		return 0;
 	}		
 
+#ifdef TDB_TRACE
+	/* store seqnum now, before reading becomes illegal. */
+	tdb_ofs_read(tdb, TDB_SEQNUM_OFS, &tdb->transaction_prepare_seqnum);
+#endif
+
 	/* check for a null transaction */
 	if (tdb->transaction->blocks == NULL) {
-		tdb_transaction_cancel_internal(tdb);
 		return 0;
 	}
 
@@ -883,14 +919,14 @@ int tdb_transaction_commit(struct tdb_context *tdb)
 	   nested their locks properly, so fail the transaction */
 	if (tdb->num_locks || tdb->global_lock.count) {
 		tdb->ecode = TDB_ERR_LOCK;
-		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: locks pending on commit\n"));
+		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: locks pending on commit\n"));
 		tdb_transaction_cancel_internal(tdb);
 		return -1;
 	}
 
 	/* upgrade the main transaction lock region to a write lock */
 	if (tdb_brlock_upgrade(tdb, FREELIST_TOP, 0) == -1) {
-		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: failed to upgrade hash locks\n"));
+		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: failed to upgrade hash locks\n"));
 		tdb->ecode = TDB_ERR_LOCK;
 		tdb_transaction_cancel_internal(tdb);
 		return -1;
@@ -899,7 +935,7 @@ int tdb_transaction_commit(struct tdb_context *tdb)
 	/* get the global lock - this prevents new users attaching to the database
 	   during the commit */
 	if (tdb_brlock(tdb, GLOBAL_LOCK, F_WRLCK, F_SETLKW, 0, 1) == -1) {
-		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: failed to get global lock\n"));
+		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: failed to get global lock\n"));
 		tdb->ecode = TDB_ERR_LOCK;
 		tdb_transaction_cancel_internal(tdb);
 		return -1;
@@ -907,21 +943,23 @@ int tdb_transaction_commit(struct tdb_context *tdb)
 
 	if (!(tdb->flags & TDB_NOSYNC)) {
 		/* write the recovery data to the end of the file */
-		if (transaction_setup_recovery(tdb, &magic_offset) == -1) {
-			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: failed to setup recovery data\n"));
+		if (transaction_setup_recovery(tdb, &tdb->transaction->magic_offset) == -1) {
+			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_prepare_commit: failed to setup recovery data\n"));
 			tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);
 			tdb_transaction_cancel_internal(tdb);
 			return -1;
 		}
 	}
 
+	tdb->transaction->prepared = true;
+
 	/* expand the file to the new size if needed */
 	if (tdb->map_size != tdb->transaction->old_map_size) {
 		if (methods->tdb_expand_file(tdb, tdb->transaction->old_map_size, 
 					     tdb->map_size - 
 					     tdb->transaction->old_map_size) == -1) {
 			tdb->ecode = TDB_ERR_IO;
-			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: expansion failed\n"));
+			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_prepare_commit: expansion failed\n"));
 			tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);
 			tdb_transaction_cancel_internal(tdb);
 			return -1;
@@ -930,6 +968,68 @@ int tdb_transaction_commit(struct tdb_context *tdb)
 		methods->tdb_oob(tdb, tdb->map_size + 1, 1);
 	}
 
+	/* Keep the global lock until the actual commit */
+
+	return 0;
+}
+
+/*
+   prepare to commit the current transaction
+*/
+int tdb_transaction_prepare_commit(struct tdb_context *tdb)
+{	
+	tdb_trace(tdb, "tdb_transaction_prepare_commit");
+	return tdb_transaction_prepare_commit_internal(tdb);
+}
+
+/*
+  commit the current transaction
+*/
+int tdb_transaction_commit(struct tdb_context *tdb)
+{	
+	const struct tdb_methods *methods;
+	int i;
+
+	if (tdb->transaction == NULL) {
+		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: no transaction\n"));
+		return -1;
+	}
+
+	/* If we've prepared, can't read seqnum. */
+	if (tdb->transaction->prepared) {
+		tdb_trace_seqnum(tdb, tdb->transaction_prepare_seqnum,
+				 "tdb_transaction_commit");
+	} else {
+		tdb_trace(tdb, "tdb_transaction_commit");
+	}
+
+	if (tdb->transaction->transaction_error) {
+		tdb->ecode = TDB_ERR_IO;
+		tdb_transaction_cancel(tdb);
+		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: transaction error pending\n"));
+		return -1;
+	}
+
+
+	if (tdb->transaction->nesting != 0) {
+		tdb->transaction->nesting--;
+		return 0;
+	}
+
+	/* check for a null transaction */
+	if (tdb->transaction->blocks == NULL) {
+		tdb_transaction_cancel_internal(tdb);
+		return 0;
+	}
+
+	if (!tdb->transaction->prepared) {
+		int ret = tdb_transaction_prepare_commit_internal(tdb);
+		if (ret)
+			return ret;
+	}
+
+	methods = tdb->transaction->io_methods;
+
 	/* perform all the writes */
 	for (i=0;i<tdb->transaction->num_blocks;i++) {
 		tdb_off_t offset;
@@ -971,17 +1071,6 @@ int tdb_transaction_commit(struct tdb_context *tdb)
 		if (transaction_sync(tdb, 0, tdb->map_size) == -1) {
 			return -1;
 		}
-
-		/* remove the recovery marker */
-		if (methods->tdb_write(tdb, magic_offset, &zero, 4) == -1) {
-			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: failed to remove recovery magic\n"));
-			return -1;
-		}
-
-		/* ensure the recovery marker has been removed on disk */
-		if (transaction_sync(tdb, magic_offset, 4) == -1) {
-			return -1;
-		}
 	}
 
 	tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);