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Re: postgres crash on CURSORS

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: postgres crash on CURSORS
Date: 2000-04-04 20:06:27
Message-ID: 12072.954878787@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> I have found I can crash the backend with the following queries:
> 	test=> BEGIN WORK;
> 	BEGIN
> 	test=> DECLARE bigtable_cursor CURSOR FOR
test-> SELECT * FROM bigtable;
> 	SELECT
> 	test=> FETCH 3 prior FROM bigtable_cursor;
> 	ERROR:  parser: parse error at or near "prior"
> 	test=> FETCH prior FROM bigtable_cursor;
> 	pqReadData() -- backend closed the channel unexpectedly.
> 	        This probably means the backend terminated abnormally
> 	        before or while processing the request.
> 	The connection to the server was lost. Attempting reset: Succeeded.

Problem appears to be due to trying to bull ahead with processing after
the current transaction has been aborted by an error.  The immediate
cause is these lines in postgres.c:

            /*
             * We have to set query SnapShot in the case of FETCH or COPY TO.
             */
            if (nodeTag(querytree->utilityStmt) == T_FetchStmt ||
                (nodeTag(querytree->utilityStmt) == T_CopyStmt && 
                ((CopyStmt *)(querytree->utilityStmt))->direction != FROM))
                SetQuerySnapshot();

which are executed without having bothered to check for aborted state.
I think this code should be removed from postgres.c, and the
SetQuerySnapshot call instead made from the Fetch and Copy arms of the
switch statement in ProcessUtility() (utility.c), after doing
CHECK_IF_ABORTED in each case.

			regards, tom lane

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Subject: Re: postgres crash on CURSORS
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