tdb: detect tdb store of identical records and skip

This can help with ldb where we rewrite the index records
(cherry picked from commit 2466798cc4cb46e8689d43bae0403119266dbe9e)

diff --git a/lib/tdb/common/tdb.c b/lib/tdb/common/tdb.c
index 0389d3cb961f83ceb6ab1eaa3246b5d99a2ca88a..564c5fed5c8331fcd713a0267e6478588559bfbd 100644 (file)
--- a/lib/tdb/common/tdb.c
+++ b/lib/tdb/common/tdb.c
@@ -121,6 +121,7 @@ tdb_off_t tdb_find_lock_hash(struct tdb_context *tdb, TDB_DATA key, uint32_t has
        return rec_ptr;
 }
 
+static TDB_DATA _tdb_fetch(struct tdb_context *tdb, TDB_DATA key);
 
 /* update an entry in place - this only works if the new data size
    is <= the old data size and the key exists.
@@ -135,6 +136,25 @@ static int tdb_update_hash(struct tdb_context *tdb, TDB_DATA key, uint32_t hash,
        if (!(rec_ptr = tdb_find(tdb, key, hash, &rec)))
                return -1;
 
+       /* it could be an exact duplicate of what is there - this is
+        * surprisingly common (eg. with a ldb re-index). */
+       if (rec.key_len == key.dsize && 
+           rec.data_len == dbuf.dsize &&
+           rec.full_hash == hash) {
+               TDB_DATA data = _tdb_fetch(tdb, key);
+               if (data.dsize == dbuf.dsize &&
+                   memcmp(data.dptr, dbuf.dptr, data.dsize) == 0) {
+                       if (data.dptr) {
+                               free(data.dptr);
+                       }
+                       return 0;
+               }
+               if (data.dptr) {
+                       free(data.dptr);
+               }
+       }
+        
+
        /* must be long enough key, data and tailer */
        if (rec.rec_len < key.dsize + dbuf.dsize + sizeof(tdb_off_t)) {
                tdb->ecode = TDB_SUCCESS; /* Not really an error */