Install a search tree depth limit in GIN bulk-insert operations, to prevent

them from degrading badly when the input is sorted or nearly so.  In this
scenario the tree is unbalanced to the point of becoming a mere linked list,
so insertions become O(N^2).  The easiest and most safely back-patchable
solution is to stop growing the tree sooner, ie limit the growth of N.  We
might later consider a rebalancing tree algorithm, but it's not clear that
the benefit would be worth the cost and complexity.  Per report from Sergey
Burladyan and an earlier complaint from Heikki.

Back-patch to 8.2; older versions didn't have GIN indexes.

diff --git a/src/backend/access/gin/gininsert.c b/src/backend/access/gin/gininsert.c
index 919d5c912844349e70a51d30ffb0e90b93470ab8..6089f622d143fee04dcf0b4d78ae779f75efeac0 100644 (file)
--- a/src/backend/access/gin/gininsert.c
+++ b/src/backend/access/gin/gininsert.c
@@ -241,7 +241,8 @@ ginBuildCallback(Relation index, HeapTuple htup, Datum *values,
         * we use only half maintenance_work_mem, because there is some leaks
         * during insertion and extract values
         */
-       if (buildstate->accum.allocatedMemory >= maintenance_work_mem * 1024L / 2L)
+       if (buildstate->accum.allocatedMemory >= maintenance_work_mem * 1024L / 2L ||
+               buildstate->accum.maxdepth > GIN_MAX_TREE_DEPTH)
        {
                ItemPointerData *list;
                Datum           entry;

diff --git a/src/include/access/gin.h b/src/include/access/gin.h
index 3e16b4e9c8647bbf49ce099e140279ff8f93c4c3..7aea9540635d79037d709518a27eb6793b88fd71 100644 (file)
--- a/src/include/access/gin.h
+++ b/src/include/access/gin.h
@@ -33,6 +33,14 @@
 
 typedef XLogRecPtr GinNSN;
 
+/*
+ * Max depth allowed in search tree during bulk inserts.  This is to keep from
+ * degenerating to O(N^2) behavior when the tree is unbalanced due to sorted
+ * or nearly-sorted input.  (Perhaps it would be better to use a balanced-tree
+ * algorithm, but in common cases that would only add useless overhead.)
+ */
+#define GIN_MAX_TREE_DEPTH 100
+
 /*
  * Page opaque data in a inverted index page.
  */
@@ -314,12 +322,9 @@ extern IndexTuple ginPageGetLinkItup(Buffer buf);
 
 /* gindatapage.c */
 extern int     compareItemPointers(ItemPointer a, ItemPointer b);
-extern void
-MergeItemPointers(
-                                 ItemPointerData *dst,
+extern void MergeItemPointers(ItemPointerData *dst,
                                  ItemPointerData *a, uint32 na,
-                                 ItemPointerData *b, uint32 nb
-);
+                                 ItemPointerData *b, uint32 nb);
 
 extern void GinDataPageAddItem(Page page, void *data, OffsetNumber offset);
 extern void PageDeletePostingItem(Page page, OffsetNumber offset);