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Fix pg_xlogdump so that it handles cross-page XLP_FIRST_IS_CONTRECORD record.
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
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@ -866,46 +866,83 @@ XLogRecPtr
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XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr)
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{
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XLogReaderState saved_state = *state;
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XLogRecPtr targetPagePtr;
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XLogRecPtr tmpRecPtr;
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int targetRecOff;
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XLogRecPtr found = InvalidXLogRecPtr;
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uint32 pageHeaderSize;
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XLogPageHeader header;
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int readLen;
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char *errormsg;
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Assert(!XLogRecPtrIsInvalid(RecPtr));
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targetRecOff = RecPtr % XLOG_BLCKSZ;
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/* scroll back to page boundary */
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targetPagePtr = RecPtr - targetRecOff;
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/* Read the page containing the record */
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readLen = ReadPageInternal(state, targetPagePtr, targetRecOff);
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if (readLen < 0)
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goto err;
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header = (XLogPageHeader) state->readBuf;
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pageHeaderSize = XLogPageHeaderSize(header);
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/* make sure we have enough data for the page header */
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readLen = ReadPageInternal(state, targetPagePtr, pageHeaderSize);
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if (readLen < 0)
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goto err;
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/* skip over potential continuation data */
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if (header->xlp_info & XLP_FIRST_IS_CONTRECORD)
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/*
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* skip over potential continuation data, keeping in mind that it may span
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* multiple pages
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*/
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tmpRecPtr = RecPtr;
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while (true)
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{
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/* record headers are MAXALIGN'ed */
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tmpRecPtr = targetPagePtr + pageHeaderSize
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+ MAXALIGN(header->xlp_rem_len);
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}
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else
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{
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tmpRecPtr = targetPagePtr + pageHeaderSize;
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XLogRecPtr targetPagePtr;
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int targetRecOff;
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uint32 pageHeaderSize;
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int readLen;
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/*
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* Compute targetRecOff. It should typically be equal or greater than
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* short page-header since a valid record can't start anywhere before
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* that, except when caller has explicitly specified the offset that
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* falls somewhere there or when we are skipping multi-page
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* continuation record. It doesn't matter though because
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* ReadPageInternal() is prepared to handle that and will read at least
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* short page-header worth of data
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*/
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targetRecOff = tmpRecPtr % XLOG_BLCKSZ;
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/* scroll back to page boundary */
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targetPagePtr = tmpRecPtr - targetRecOff;
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/* Read the page containing the record */
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readLen = ReadPageInternal(state, targetPagePtr, targetRecOff);
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if (readLen < 0)
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goto err;
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header = (XLogPageHeader) state->readBuf;
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pageHeaderSize = XLogPageHeaderSize(header);
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/* make sure we have enough data for the page header */
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readLen = ReadPageInternal(state, targetPagePtr, pageHeaderSize);
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if (readLen < 0)
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goto err;
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/* skip over potential continuation data */
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if (header->xlp_info & XLP_FIRST_IS_CONTRECORD)
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{
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/*
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* If the length of the remaining continuation data is more than
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* what can fit in this page, the continuation record crosses over
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* this page. Read the next page and try again. xlp_rem_len in the
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* next page header will contain the remaining length of the
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* continuation data
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*
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* Note that record headers are MAXALIGN'ed
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*/
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if (MAXALIGN(header->xlp_rem_len) > (XLOG_BLCKSZ - pageHeaderSize))
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tmpRecPtr = targetPagePtr + XLOG_BLCKSZ;
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else
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{
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/*
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* The previous continuation record ends in this page. Set
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* tmpRecPtr to point to the first valid record
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*/
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tmpRecPtr = targetPagePtr + pageHeaderSize
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+ MAXALIGN(header->xlp_rem_len);
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break;
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}
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}
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else
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{
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tmpRecPtr = targetPagePtr + pageHeaderSize;
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break;
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}
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}
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/*
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