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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2015-08-21 20:32:11 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2015-08-21 20:32:41 -0400 |
| commit | 7c57449fc5855361d3a69374192c58fb68ce3e67 (patch) | |
| tree | 7c2826c477d2d77d32328d6d1c2c86f42e3d7a79 | |
| parent | e41718fa1eb67210808c9b5a084fc1aaffde5b35 (diff) | |
| download | postgresql-7c57449fc5855361d3a69374192c58fb68ce3e67.tar.gz | |
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 7de785d725..a9b544ab0e 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)); |