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Adjust assertion in XLogDecodeNextRecord.
As written, if you use XLogBeginRead() to position an xlogreader at the beginning of a WAL page and then try to read WAL, this assertion will fail. However, the header comment for XLogBeginRead() claims that positioning an xlogreader at the beginning of a page is valid, and the code here is perfectly able to cope with it. It's only the assertion that causes trouble. So relax it. This is formally a bug in all supported branches, but as it doesn't seem to have any consequences for current uses of the xlogreader facility, no back-patch, at least for now. Dilip Kumar and Robert Haas Discussion: http://postgr.es/m/CA+TgmoaJSs2_7WHW2GzFYe9+zfPtxBKvT3GW47+x=ptUE=cULw@mail.gmail.com
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src/backend/access/transam/xlogreader.c

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -576,10 +576,11 @@ XLogDecodeNextRecord(XLogReaderState *state, bool nonblocking)
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/*
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* Caller supplied a position to start at.
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*
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* In this case, NextRecPtr should already be pointing to a valid
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* record starting position.
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* In this case, NextRecPtr should already be pointing either to a
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* valid record starting position or alternatively to the beginning of
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* a page. See the header comments for XLogBeginRead.
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*/
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Assert(XRecOffIsValid(RecPtr));
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Assert(RecPtr % XLOG_BLCKSZ == 0 || XRecOffIsValid(RecPtr));
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randAccess = true;
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}
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