It turns out that the item size limit for btree indexes is about BLCKSZ/3,

not BLCKSZ/2 as some of us thought.  Add check for oversize item so that
failure is detected before corrupting the index, not after.

diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index ed8e3ac..57c5799 100644 (file)
--- a/src/backend/access/nbtree/nbtinsert.c
+++ b/src/backend/access/nbtree/nbtinsert.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.51 1999/11/22 17:55:54 momjian Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.52 1999/12/26 03:48:22 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -268,6 +268,18 @@ _bt_insertonpg(Relation rel,
                                                                                 * consistent */
 
        /*
+        * Check whether the item can fit on a btree page at all.
+        * (Eventually, we ought to try to apply TOAST methods if not.)
+        * We actually need to be able to fit three items on every page,
+        * so restrict any one item to 1/3 the per-page available space.
+        * Note that at this point, itemsz doesn't include the ItemId.
+        */
+       if (itemsz > (PageGetPageSize(page)-sizeof(PageHeaderData)-MAXALIGN(sizeof(BTPageOpaqueData)))/3 - sizeof(ItemIdData))
+               elog(ERROR, "btree: index item size %d exceeds maximum %d",
+                        itemsz,
+                        (PageGetPageSize(page)-sizeof(PageHeaderData)-MAXALIGN(sizeof(BTPageOpaqueData)))/3 - sizeof(ItemIdData));
+
+       /*
         * If we have to insert item on the leftmost page which is the first
         * page in the chain of duplicates then: 1. if scankey == hikey (i.e.
         * - new duplicate item) then insert it here; 2. if scankey < hikey
@@ -342,36 +354,42 @@ _bt_insertonpg(Relation rel,
        {
                OffsetNumber offnum = (P_RIGHTMOST(lpageop)) ? P_HIKEY : P_FIRSTKEY;
                OffsetNumber maxoff = PageGetMaxOffsetNumber(page);
-               ItemId          itid;
-               BTItem          previtem,
-                                       chkitem;
-               Size            maxsize;
-               Size            currsize;
-
-               itid = PageGetItemId(page, offnum);
-               previtem = (BTItem) PageGetItem(page, itid);
-               maxsize = currsize = (ItemIdGetLength(itid) + sizeof(ItemIdData));
-               for (offnum = OffsetNumberNext(offnum);
-                        offnum <= maxoff; offnum = OffsetNumberNext(offnum))
+
+               if (offnum < maxoff)    /* can't split unless at least 2 items... */
                {
+                       ItemId          itid;
+                       BTItem          previtem,
+                                               chkitem;
+                       Size            maxsize;
+                       Size            currsize;
+
+                       /* find largest group of identically-keyed items on page */
                        itid = PageGetItemId(page, offnum);
-                       chkitem = (BTItem) PageGetItem(page, itid);
-                       if (!_bt_itemcmp(rel, keysz, previtem, chkitem,
-                                                        BTEqualStrategyNumber))
+                       previtem = (BTItem) PageGetItem(page, itid);
+                       maxsize = currsize = (ItemIdGetLength(itid) + sizeof(ItemIdData));
+                       for (offnum = OffsetNumberNext(offnum);
+                                offnum <= maxoff; offnum = OffsetNumberNext(offnum))
                        {
-                               if (currsize > maxsize)
-                                       maxsize = currsize;
-                               currsize = 0;
-                               previtem = chkitem;
+                               itid = PageGetItemId(page, offnum);
+                               chkitem = (BTItem) PageGetItem(page, itid);
+                               if (!_bt_itemcmp(rel, keysz, previtem, chkitem,
+                                                                BTEqualStrategyNumber))
+                               {
+                                       if (currsize > maxsize)
+                                               maxsize = currsize;
+                                       currsize = 0;
+                                       previtem = chkitem;
+                               }
+                               currsize += (ItemIdGetLength(itid) + sizeof(ItemIdData));
                        }
-                       currsize += (ItemIdGetLength(itid) + sizeof(ItemIdData));
+                       if (currsize > maxsize)
+                               maxsize = currsize;
+                       /* Decide to split if largest group is > 1/2 page size */
+                       maxsize += sizeof(PageHeaderData) +
+                               MAXALIGN(sizeof(BTPageOpaqueData));
+                       if (maxsize >= PageGetPageSize(page) / 2)
+                               do_split = true;
                }
-               if (currsize > maxsize)
-                       maxsize = currsize;
-               maxsize += sizeof(PageHeaderData) +
-                       MAXALIGN(sizeof(BTPageOpaqueData));
-               if (maxsize >= PageGetPageSize(page) / 2)
-                       do_split = true;
        }
 
        if (do_split)