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

diff --git a/ccan/tdb/tdb.c b/ccan/tdb/tdb.c
index c44987a14e01f343c008e403eb789bd3973a33dd..82ad6058032066b95e91b844431407b4a53de64b 100644 (file)
--- a/ccan/tdb/tdb.c
+++ b/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)
 {

diff --git a/ccan/tdb/tdb.h b/ccan/tdb/tdb.h
index a2443ff4539232cdbfe3f143f56b7b2ae740967f..43282e57ff8e824a80fdb784d53ab640c051cac3 100644 (file)
--- a/ccan/tdb/tdb.h
+++ b/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);

diff --git a/ccan/tdb/tdb_private.h b/ccan/tdb/tdb_private.h
index ceb4358cd31b5f103f896fafc3ddb349be915d69..b6eae478736696541d0767f5a90a529ba5b1d459 100644 (file)
--- a/ccan/tdb/tdb_private.h
+++ b/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;
 };
 

diff --git a/ccan/tdb/tools/keywords.c b/ccan/tdb/tools/keywords.c
index 461a61e7df156f8a916bc069613f3d3694240177..32ca447b4bfa45efac087642aa2bba1e441e7ccf 100644 (file)
--- a/ccan/tdb/tools/keywords.c
+++ b/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,},
       {""},

diff --git a/ccan/tdb/tools/keywords.gperf b/ccan/tdb/tools/keywords.gperf
index 676b64e62827c1d4b890f3c4b07f954866367a89..387a6588e6601b5af08d2a0c413493650f0c66f8 100644 (file)
--- a/ccan/tdb/tools/keywords.gperf
+++ b/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,

diff --git a/ccan/tdb/tools/replay_trace.c b/ccan/tdb/tools/replay_trace.c
index 67809d82093e57765cd0ac5e12dfc4644b869799..651a67e97b1cc5a17f4b732960dfaf7e0c0c7495 100644 (file)
--- a/ccan/tdb/tools/replay_trace.c
+++ b/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;

diff --git a/ccan/tdb/tools/tdbtorture.c b/ccan/tdb/tools/tdbtorture.c
index 796fe26cc008eeba973bf9812ca731bf12fd24ce..83a5c99e5e75fd20b1f34843639adbeac097ed46 100644 (file)
--- a/ccan/tdb/tools/tdbtorture.c
+++ b/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");
                }

diff --git a/ccan/tdb/transaction.c b/ccan/tdb/transaction.c
index a23bb60427c574a5ac9c7f25ef7c82f32c9c6e0c..4c261598972dad139442abc12e03ed3a37cc5379 100644 (file)
--- a/ccan/tdb/transaction.c
+++ b/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);