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authorTom Lane <tgl@sss.pgh.pa.us>2015-08-21 20:32:11 -0400
committerTom Lane <tgl@sss.pgh.pa.us>2015-08-21 20:32:37 -0400
commit87b8c9e12f3025b70bd040c42d7d5f39ef9314bc (patch)
treee055d81d26ea3f1b7a2b3e93195649a82ef36786
parent1d190d095ff8e7d11877fc7d4dc82727871a91c1 (diff)
downloadpostgresql-87b8c9e12f3025b70bd040c42d7d5f39ef9314bc.tar.gz
postgresql-87b8c9e12f3025b70bd040c42d7d5f39ef9314bc.zip
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
-rw-r--r--src/backend/executor/spi.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c
index 7f4624cba59..c9e43fb047a 100644
--- a/src/backend/executor/spi.c
+++ b/src/backend/executor/spi.c
@@ -1622,7 +1622,8 @@ 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));