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Fix platform-specific performance regression in logtape.c. 

Commit 24d85952 made a change that indirectly caused a performance
regression by triggering a change in the way GCC optimizes memcpy() on
some platforms.

The behavior seemed to contradict a GCC document, so I filed a report:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95556

This patch implements a narrow workaround which eliminates the
regression I observed. The workaround is benign enough that it seems
unlikely to cause a different regression on another platform.

Discussion: https://postgr.es/m/99b2eab335c1592c925d8143979c8e9e81e1575f.camel@j-davis.com
This commit is contained in:
Jeff Davis 2020-06-07 09:14:24 -07:00
parent aa7927698a
commit 1fbb6c93df
1 changed files with 1 additions and 1 deletions
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2
src/backend/utils/sort/logtape.c
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@ -782,7 +782,7 @@ LogicalTapeWrite(LogicalTapeSet *lts, int tapenum,
Assert(lt->buffer_size == BLCKSZ);
while (size > 0)
{
if (lt->pos >= TapeBlockPayloadSize)
if (lt->pos >= (int) TapeBlockPayloadSize)
{
/* Buffer full, dump it out */
long nextBlockNumber;