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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 20:32:17 -0400
commit68a14ca74be03ab189b83c2bbf0b68c5d1daba44 (patch)
tree6b3d5430e911c0475197836953dce1ab74973607 /src/backend/executor
parent93fcb4ae3e4b20e8562f0a8cab3a3a486ad84e76 (diff)
downloadpostgresql-68a14ca74be03ab189b83c2bbf0b68c5d1daba44.tar.gz
postgresql-68a14ca74be03ab189b83c2bbf0b68c5d1daba44.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
Diffstat (limited to 'src/backend/executor')
-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 d544ad9c106..300401e01f9 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));