From ec97db399f1eccda6652d44b99d5363728832eb7 Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Thu, 18 Aug 2022 12:15:55 -0400 Subject: [PATCH] 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 --- src/backend/access/transam/xlogreader.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c index 06e91547dd..f17e80948d 100644 --- a/src/backend/access/transam/xlogreader.c +++ b/src/backend/access/transam/xlogreader.c @@ -576,10 +576,11 @@ XLogDecodeNextRecord(XLogReaderState *state, bool nonblocking) /* * Caller supplied a position to start at. * - * In this case, NextRecPtr should already be pointing to a valid - * record starting position. + * In this case, NextRecPtr should already be pointing either to a + * valid record starting position or alternatively to the beginning of + * a page. See the header comments for XLogBeginRead. */ - Assert(XRecOffIsValid(RecPtr)); + Assert(RecPtr % XLOG_BLCKSZ == 0 || XRecOffIsValid(RecPtr)); randAccess = true; }