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author | Tom Lane <tgl@sss.pgh.pa.us> | 2015-08-21 20:32:11 -0400 |
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committer | Tom Lane <tgl@sss.pgh.pa.us> | 2015-08-21 20:32:37 -0400 |
commit | 87b8c9e12f3025b70bd040c42d7d5f39ef9314bc (patch) | |
tree | e055d81d26ea3f1b7a2b3e93195649a82ef36786 | |
parent | 1d190d095ff8e7d11877fc7d4dc82727871a91c1 (diff) | |
download | postgresql-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.c | 3 |
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)); |