diff options
| 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 20:32:33 -0400 |
| commit | d951d6065dbf11cca35fd1f7741156d0c55dcd7e (patch) | |
| tree | ec06a3cf285b1ae1be34c10761ba5eb45791feb6 /src/backend/executor | |
| parent | dadef8af2e71368da8ad0212389771b1fce22ee2 (diff) | |
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.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c index 98cf744f89c..3746ffdbcdb 100644 --- a/src/backend/executor/spi.c +++ b/src/backend/executor/spi.c @@ -1674,7 +1674,8 @@ 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)); |