From 6e5d9f278c1209936d973930996857f55e119cd8 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 21 Aug 2015 20:32:11 -0400 Subject: [PATCH] Avoid O(N^2) behavior when enlarging SPI tuple table in spi_printtup(). For no obvious reason, spi_printtup() was coded to enlarge the tuple pointer table by just 256 slots at a time, rather than doubling the size at each reallocation, as is our usual habit. For very large SPI results, this makes for O(N^2) time spent in repalloc(), which of course soon comes to dominate the runtime. Use the standard doubling approach instead. This is a longstanding performance bug, so back-patch to all active branches. Neil Conway --- src/backend/executor/spi.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c index d544ad9c10..300401e01f 100644 --- a/src/backend/executor/spi.c +++ b/src/backend/executor/spi.c @@ -1797,7 +1797,8 @@ spi_printtup(TupleTableSlot *slot, DestReceiver *self) if (tuptable->free == 0) { - tuptable->free = 256; + /* Double the size of the pointer array */ + tuptable->free = tuptable->alloced; tuptable->alloced += tuptable->free; tuptable->vals = (HeapTuple *) repalloc(tuptable->vals, tuptable->alloced * sizeof(HeapTuple));