pgsql: Adjust assertion in XLogDecodeNextRecord.

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

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ec97db399f1eccda6652d44b99d5363728832eb7

Modified Files
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src/backend/access/transam/xlogreader.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)