From b56fb691b0033f9b86e0552bd5adfd485f05eef6 Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Thu, 6 Oct 2016 09:46:40 +0300 Subject: [PATCH] Fix excessive memory consumption in the new sort pre-reading code. LogicalTapeRewind() should not allocate large read buffer, if the tape is completely empty. The calling code relies on that, for its calculation of how much memory to allocate for the read buffers. That lead to massive overallocation of memory, if maxTapes was high, but only a few tapes were actually used. Reported by Tomas Vondra Discussion: <7303da46-daf7-9c68-3cc1-9f83235cf37e@2ndquadrant.com> --- src/backend/utils/sort/logtape.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/src/backend/utils/sort/logtape.c b/src/backend/utils/sort/logtape.c index caa6960b957..6cc06b24e0d 100644 --- a/src/backend/utils/sort/logtape.c +++ b/src/backend/utils/sort/logtape.c @@ -778,11 +778,16 @@ LogicalTapeRewind(LogicalTapeSet *lts, int tapenum, bool forWrite) datablocknum = ltsRewindFrozenIndirectBlock(lts, lt->indirect); } - /* Allocate a read buffer */ + /* Allocate a read buffer (unless the tape is empty) */ if (lt->buffer) pfree(lt->buffer); - lt->buffer = palloc(lt->read_buffer_size); - lt->buffer_size = lt->read_buffer_size; + lt->buffer = NULL; + lt->buffer_size = 0; + if (datablocknum != -1L) + { + lt->buffer = palloc(lt->read_buffer_size); + lt->buffer_size = lt->read_buffer_size; + } /* Read the first block, or reset if tape is empty */ lt->curBlockNumber = 0L;