112 lines
4.0 KiB
Diff
112 lines
4.0 KiB
Diff
Back-patch upstream patch to cope with a gcc 4.6.0 bug. This will be
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in PG 9.0.5 and later, but we need it in Fedora *now* because the bug
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breaks WAL replay, thus causing crash recovery failures as well as the
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originally reported symptom of frequent reconnections during standby.
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commit 45d792f70272ed57b932816562f31c2f79426c2a
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Author: Tom Lane <tgl@sss.pgh.pa.us>
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Date: Fri Jun 10 17:03:11 2011 -0400
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Work around gcc 4.6.0 bug that breaks WAL replay.
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ReadRecord's habit of using both direct references to tmpRecPtr and
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references to *RecPtr (which is pointing at tmpRecPtr) triggers an
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optimization bug in gcc 4.6.0, which apparently has forgotten about
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aliasing rules. Avoid the compiler bug, and make the code more readable
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to boot, by getting rid of the direct references. Improve the comments
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while at it.
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Back-patch to all supported versions, in case they get built with 4.6.0.
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Tom Lane, with some cosmetic suggestions from Alex Hunsaker
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diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
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index bf8075d..6c18db4 100644
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--- a/src/backend/access/transam/xlog.c
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+++ b/src/backend/access/transam/xlog.c
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@@ -3676,23 +3676,32 @@ ReadRecord(XLogRecPtr *RecPtr, int emode, bool fetching_ckpt)
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RecPtr = &tmpRecPtr;
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/*
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- * Align recptr to next page if no more records can fit on the current
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- * page.
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+ * RecPtr is pointing to end+1 of the previous WAL record. We must
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+ * advance it if necessary to where the next record starts. First,
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+ * align to next page if no more records can fit on the current page.
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*/
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if (XLOG_BLCKSZ - (RecPtr->xrecoff % XLOG_BLCKSZ) < SizeOfXLogRecord)
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- {
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- NextLogPage(tmpRecPtr);
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- /* We will account for page header size below */
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- }
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+ NextLogPage(*RecPtr);
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- if (tmpRecPtr.xrecoff >= XLogFileSize)
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+ /* Check for crossing of xlog segment boundary */
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+ if (RecPtr->xrecoff >= XLogFileSize)
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{
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- (tmpRecPtr.xlogid)++;
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- tmpRecPtr.xrecoff = 0;
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+ (RecPtr->xlogid)++;
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+ RecPtr->xrecoff = 0;
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}
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+
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+ /*
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+ * If at page start, we must skip over the page header. But we can't
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+ * do that until we've read in the page, since the header size is
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+ * variable.
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+ */
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}
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else
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{
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+ /*
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+ * In this case, the passed-in record pointer should already be
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+ * pointing to a valid record starting position.
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+ */
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if (!XRecOffIsValid(RecPtr->xrecoff))
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ereport(PANIC,
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(errmsg("invalid record offset at %X/%X",
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@@ -3721,11 +3730,13 @@ retry:
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if (targetRecOff == 0)
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{
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/*
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- * Can only get here in the continuing-from-prev-page case, because
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- * XRecOffIsValid eliminated the zero-page-offset case otherwise. Need
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- * to skip over the new page's header.
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+ * At page start, so skip over page header. The Assert checks that
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+ * we're not scribbling on caller's record pointer; it's OK because we
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+ * can only get here in the continuing-from-prev-record case, since
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+ * XRecOffIsValid rejected the zero-page-offset case otherwise.
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*/
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- tmpRecPtr.xrecoff += pageHeaderSize;
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+ Assert(RecPtr == &tmpRecPtr);
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+ RecPtr->xrecoff += pageHeaderSize;
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targetRecOff = pageHeaderSize;
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}
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else if (targetRecOff < pageHeaderSize)
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diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
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index 3f0930f..367de37 100644
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--- a/src/include/access/xlog_internal.h
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+++ b/src/include/access/xlog_internal.h
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@@ -154,13 +154,13 @@ typedef XLogLongPageHeaderData *XLogLongPageHeader;
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/* Align a record pointer to next page */
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#define NextLogPage(recptr) \
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do { \
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- if (recptr.xrecoff % XLOG_BLCKSZ != 0) \
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- recptr.xrecoff += \
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- (XLOG_BLCKSZ - recptr.xrecoff % XLOG_BLCKSZ); \
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- if (recptr.xrecoff >= XLogFileSize) \
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+ if ((recptr).xrecoff % XLOG_BLCKSZ != 0) \
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+ (recptr).xrecoff += \
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+ (XLOG_BLCKSZ - (recptr).xrecoff % XLOG_BLCKSZ); \
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+ if ((recptr).xrecoff >= XLogFileSize) \
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{ \
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- (recptr.xlogid)++; \
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- recptr.xrecoff = 0; \
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+ ((recptr).xlogid)++; \
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+ (recptr).xrecoff = 0; \
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} \
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} while (0)
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