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Correct StartupSUBTRANS for page wraparound

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StartupSUBTRANS() incorrectly handled cases near the max pageid in the subtrans
data structure, which in some cases could lead to errors in startup for Hot
Standby.
This patch wraps the pageids correctly, avoiding any such errors.
Identified by exhaustive crash testing by Jeff Janes.

Jeff Janes
This commit is contained in:
Simon Riggs 2016-02-19 08:31:39 +00:00
parent 6f43c4d348
commit c479024d32
1 changed files with 5 additions and 1 deletions
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6
src/backend/access/transam/subtrans.c
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@ -44,7 +44,8 @@
* 0xFFFFFFFF/SUBTRANS_XACTS_PER_PAGE, and segment numbering at
* 0xFFFFFFFF/SUBTRANS_XACTS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need take no
* explicit notice of that fact in this module, except when comparing segment
* and page numbers in TruncateSUBTRANS (see SubTransPagePrecedes).
* and page numbers in TruncateSUBTRANS (see SubTransPagePrecedes) and zeroing
* them in StartupSUBTRANS.
*/
/* We need four bytes per xact */
@ -253,6 +254,9 @@ StartupSUBTRANS(TransactionId oldestActiveXID)
{
(void) ZeroSUBTRANSPage(startPage);
startPage++;
/* must account for wraparound */
if (startPage > TransactionIdToPage(MaxTransactionId))
startPage=0;
}
(void) ZeroSUBTRANSPage(startPage);