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 ed8e3ac324d768a4a91e2a67d1d73b9b943c78da..57c57997e3c7ecb8adc85fefa8a84a9c6e86dc53 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 $
  *
  *-------------------------------------------------------------------------
  */
@@ -267,6 +267,18 @@ _bt_insertonpg(Relation rel,
                                         * this but we need to be
                                         * 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.
@@ -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)