postgres.git / summary / log / commit / refs

commit    43e409cea4687ec1abdcfe82cd0b80a87a8d6adc
Author:   Peter Geoghegan <pg@bowt.ie>
Date:     Mon Sep 05 18:20:05 2022 +0000

    Backpatch nbtree page deletion hardening.
    
    Postgres 14 commit 5b861baa taught nbtree VACUUM to tolerate buggy
    opclasses.  VACUUM's inability to locate a to-be-deleted page's downlink
    in the parent page was logged instead of throwing an error.  VACUUM
    could just press on with vacuuming the index, and vacuuming the table as
    a whole.
    
    There are now anecdotal reports of this error causing problems that were
    much more disruptive than the underlying index corruption ever could be.
    Anything that makes VACUUM unable to make forward progress against one
    table/index ultimately risks making the system enter xidStopLimit mode.
    There is no good reason to take any chances here, so backpatch the
    hardening commit.
    
    Author: Peter Geoghegan <pg@bowt.ie>
    Discussion: https://postgr.es/m/CAH2-Wzm9HR6Pow=t-iQa57zT8qmX6_M4h14F-pTtb=xFDW5FBA@mail.gmail.com
    Backpatch: 10-13 (all supported versions that lacked the hardening)


 src/backend/access/nbtree/nbtpage.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c
index ac6c38b1553..f9811b6d3c2 100644
--- a/src/backend/access/nbtree/nbtpage.c
+++ b/src/backend/access/nbtree/nbtpage.c
@@ -2388,10 +2388,26 @@ _bt_lock_subtree_parent(Relation rel, BlockNumber child, BTStack stack,
 	 */
 	pbuf = _bt_getstackbuf(rel, stack, child);
 	if (pbuf == InvalidBuffer)
-		ereport(ERROR,
+	{
+		/*
+		 * Failed to "re-find" a pivot tuple whose downlink matched our child
+		 * block number on the parent level -- the index must be corrupt.
+		 * Don't even try to delete the leafbuf subtree.  Just report the
+		 * issue and press on with vacuuming the index.
+		 *
+		 * Note: _bt_getstackbuf() recovers from concurrent page splits that
+		 * take place on the parent level.  Its approach is a near-exhaustive
+		 * linear search.  This also gives it a surprisingly good chance of
+		 * recovering in the event of a buggy or inconsistent opclass.  But we
+		 * don't rely on that here.
+		 */
+		ereport(LOG,
 				(errcode(ERRCODE_INDEX_CORRUPTED),
 				 errmsg_internal("failed to re-find parent key in index \"%s\" for deletion target page %u",
 								 RelationGetRelationName(rel), child)));
+		return false;
+	}
+
 	parent = stack->bts_blkno;
 	parentoffset = stack->bts_offset;
 


[parent: b70db6c83073]