postgres.git / summary / log / commit / refs

commit    68a14ca74be03ab189b83c2bbf0b68c5d1daba44
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Sat Aug 22 00:32:11 2015 +0000
First released in: 9.6.0, 9.0.23, 9.1.19, 9.2.14, 9.3.10, 9.4.5, 9.5.0

    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


 src/backend/executor/spi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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));


[parent: 93fcb4ae3e4b]