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Commit0f452e8

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Work around gcc 4.6.0 bug that breaks WAL replay.
ReadRecord's habit of using both direct references to tmpRecPtr andreferences to *RecPtr (which is pointing at tmpRecPtr) triggers anoptimization bug in gcc 4.6.0, which apparently has forgotten aboutaliasing rules. Avoid the compiler bug, and make the code more readableto boot, by getting rid of the direct references. Improve the commentswhile at it.Back-patch to all supported versions, in case they get built with 4.6.0.Tom Lane, with some cosmetic suggestions from Alex Hunsaker
1 parente5b50d0 commit0f452e8

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1 file changed

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  • src/backend/access/transam

1 file changed

+11
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‎src/backend/access/transam/xlog.c

Lines changed: 11 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -2931,12 +2931,12 @@ ReadRecord(XLogRecPtr *RecPtr, int emode)
29312931
gotogot_record;
29322932
}
29332933
/* align old recptr to next page */
2934-
if (tmpRecPtr.xrecoff %XLOG_BLCKSZ!=0)
2935-
tmpRecPtr.xrecoff+= (XLOG_BLCKSZ-tmpRecPtr.xrecoff %XLOG_BLCKSZ);
2936-
if (tmpRecPtr.xrecoff >=XLogFileSize)
2934+
if (RecPtr->xrecoff %XLOG_BLCKSZ!=0)
2935+
RecPtr->xrecoff+= (XLOG_BLCKSZ-RecPtr->xrecoff %XLOG_BLCKSZ);
2936+
if (RecPtr->xrecoff >=XLogFileSize)
29372937
{
2938-
(tmpRecPtr.xlogid)++;
2939-
tmpRecPtr.xrecoff=0;
2938+
(RecPtr->xlogid)++;
2939+
RecPtr->xrecoff=0;
29402940
}
29412941
/* We will account for page header size below */
29422942
}
@@ -3022,11 +3022,13 @@ ReadRecord(XLogRecPtr *RecPtr, int emode)
30223022
if (targetRecOff==0)
30233023
{
30243024
/*
3025-
* Can only get here in the continuing-from-prev-page case, because
3026-
* XRecOffIsValid eliminated the zero-page-offset case otherwise. Need
3027-
* to skip over the new page's header.
3025+
* At page start, so skip over page header. The Assert checks that
3026+
* we're not scribbling on caller's record pointer; it's OK because we
3027+
* can only get here in the continuing-from-prev-record case, since
3028+
* XRecOffIsValid rejected the zero-page-offset case otherwise.
30283029
*/
3029-
tmpRecPtr.xrecoff+=pageHeaderSize;
3030+
Assert(RecPtr==&tmpRecPtr);
3031+
RecPtr->xrecoff+=pageHeaderSize;
30303032
targetRecOff=pageHeaderSize;
30313033
}
30323034
elseif (targetRecOff<pageHeaderSize)

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