prevent O(n^2) behaviour for traverse after large numbers of deletes

diff --git a/lib/tdb/common/freelist.c b/lib/tdb/common/freelist.c
index a2c594ada7783ed155709759321d3dd075bd2d55..c47cec6e450ac99d1cdea889446dd9cbe51d4e5c 100644 (file)
--- a/lib/tdb/common/freelist.c
+++ b/lib/tdb/common/freelist.c
@@ -105,6 +105,10 @@ int tdb_free(struct tdb_context *tdb, tdb_off_t offset, struct list_struct *rec)
                goto fail;
        }
 
+#if 0
+       /* (tridge) disable 'right' merges for now as they give rise to a O(n^2) behaviour during
+          traverse which is freeing old dead records */
+
        /* Look right first (I'm an Australian, dammit) */
        right = offset + sizeof(*rec) + rec->rec_len;
        if (right + sizeof(*rec) <= tdb->map_size) {
@@ -124,6 +128,7 @@ int tdb_free(struct tdb_context *tdb, tdb_off_t offset, struct list_struct *rec)
                        rec->rec_len += sizeof(r) + r.rec_len;
                }
        }
+#endif
 
 left:
        /* Look left */
@@ -153,6 +158,23 @@ left:
 
                /* If it's free, expand to include it. */
                if (l.magic == TDB_FREE_MAGIC) {
+#if 1
+                       /* we now merge the new record into the left record, rather than the other 
+                          way around. This makes the operation O(1) instead of O(n). This change
+                          prevents traverse from being O(n^2) after a lot of deletes */
+                       l.rec_len += sizeof(*rec) + rec->rec_len;
+                       if (tdb_rec_write(tdb, left, &l) == -1) {
+                               TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: update_left failed at %u\n", left));
+                               goto fail;
+                       }
+                       if (update_tailer(tdb, left, &l) == -1) {
+                               TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: update_tailer failed at %u\n", offset));
+                               goto fail;
+                       }
+                       /* we're done. */
+                       tdb_unlock(tdb, -1, F_WRLCK);
+                       return 0;                       
+#else
                        if (remove_from_freelist(tdb, left, l.next) == -1) {
                                TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: left free failed at %u\n", left));
                                goto update;
@@ -160,6 +182,7 @@ left:
                                offset = left;
                                rec->rec_len += leftsize;
                        }
+#endif
                }
        }