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Fix pg_xlogdump so that it handles cross-page XLP_FIRST_IS_CONTRECORD record.

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Previously pg_xlogdump failed to dump the contents of the WAL file
if the file starts with the continuation WAL record which spans
more than one pages. Since pg_xlogdump assumed that the continuation
record always fits on a page, it could not find the valid WAL record to
start reading from in that case.

This patch changes pg_xlogdump so that it can handle a continuation
WAL record which crosses a page boundary and find the valid record
to start reading from.

Back-patch to 9.3 where pg_xlogdump was introduced.

Author: Pavan Deolasee
Reviewed-By: Michael Paquier and Craig Ringer
Discussion: CABOikdPsPByMiG6J01DKq6om2+BNkxHTPkOyqHM2a4oYwGKsqQ@mail.gmail.com
This commit is contained in:
Fujii Masao 2016-08-29 14:34:58 +09:00
parent 9595bffc59
commit 2802b02a54
1 changed files with 69 additions and 32 deletions
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101
src/backend/access/transam/xlogreader.c
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@ -866,46 +866,83 @@ XLogRecPtr
XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr)
{
XLogReaderState saved_state = *state;
XLogRecPtr targetPagePtr;
XLogRecPtr tmpRecPtr;
int targetRecOff;
XLogRecPtr found = InvalidXLogRecPtr;
uint32 pageHeaderSize;
XLogPageHeader header;
int readLen;
char *errormsg;
Assert(!XLogRecPtrIsInvalid(RecPtr));
targetRecOff = RecPtr % XLOG_BLCKSZ;
/* scroll back to page boundary */
targetPagePtr = RecPtr - targetRecOff;
/* Read the page containing the record */
readLen = ReadPageInternal(state, targetPagePtr, targetRecOff);
if (readLen < 0)
goto err;
header = (XLogPageHeader) state->readBuf;
pageHeaderSize = XLogPageHeaderSize(header);
/* make sure we have enough data for the page header */
readLen = ReadPageInternal(state, targetPagePtr, pageHeaderSize);
if (readLen < 0)
goto err;
/* skip over potential continuation data */
if (header->xlp_info & XLP_FIRST_IS_CONTRECORD)
/*
* skip over potential continuation data, keeping in mind that it may span
* multiple pages
*/
tmpRecPtr = RecPtr;
while (true)
{
/* record headers are MAXALIGN'ed */
tmpRecPtr = targetPagePtr + pageHeaderSize
+ MAXALIGN(header->xlp_rem_len);
}
else
{
tmpRecPtr = targetPagePtr + pageHeaderSize;
XLogRecPtr targetPagePtr;
int targetRecOff;
uint32 pageHeaderSize;
int readLen;
/*
* Compute targetRecOff. It should typically be equal or greater than
* short page-header since a valid record can't start anywhere before
* that, except when caller has explicitly specified the offset that
* falls somewhere there or when we are skipping multi-page
* continuation record. It doesn't matter though because
* ReadPageInternal() is prepared to handle that and will read at least
* short page-header worth of data
*/
targetRecOff = tmpRecPtr % XLOG_BLCKSZ;
/* scroll back to page boundary */
targetPagePtr = tmpRecPtr - targetRecOff;
/* Read the page containing the record */
readLen = ReadPageInternal(state, targetPagePtr, targetRecOff);
if (readLen < 0)
goto err;
header = (XLogPageHeader) state->readBuf;
pageHeaderSize = XLogPageHeaderSize(header);
/* make sure we have enough data for the page header */
readLen = ReadPageInternal(state, targetPagePtr, pageHeaderSize);
if (readLen < 0)
goto err;
/* skip over potential continuation data */
if (header->xlp_info & XLP_FIRST_IS_CONTRECORD)
{
/*
* If the length of the remaining continuation data is more than
* what can fit in this page, the continuation record crosses over
* this page. Read the next page and try again. xlp_rem_len in the
* next page header will contain the remaining length of the
* continuation data
*
* Note that record headers are MAXALIGN'ed
*/
if (MAXALIGN(header->xlp_rem_len) > (XLOG_BLCKSZ - pageHeaderSize))
tmpRecPtr = targetPagePtr + XLOG_BLCKSZ;
else
{
/*
* The previous continuation record ends in this page. Set
* tmpRecPtr to point to the first valid record
*/
tmpRecPtr = targetPagePtr + pageHeaderSize
+ MAXALIGN(header->xlp_rem_len);
break;
}
}
else
{
tmpRecPtr = targetPagePtr + pageHeaderSize;
break;
}
}
/*