From: | Bernd Helmle <mailings(at)oopsware(dot)de> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andres Freund <andres(at)2ndquadrant(dot)com> |
Cc: | Sven Wegener <sven(dot)wegener(at)stealer(dot)net>, pgsql-hackers(at)postgresql(dot)org, pgsql-general(at)postgresql(dot)org, pgsql-bugs(at)postgresql(dot)org |
Subject: | Re: [GENERAL] Re: [BUGS] COPY TO returning empty result with parallel ALTER TABLE |
Date: | 2014-11-04 23:14:42 |
Message-ID: | FF3CF50F040B5D1AE1381AB1@localhost |
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Lists: | pgsql-bugs pgsql-general pgsql-hackers |
--On 4. November 2014 17:18:14 -0500 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Yeah, and I think that it's entirely reasonable for rewriting ALTER TABLEs
> to update the xmin of the rewritten tuples; after all, the output data
> could be arbitrarily different from what the previous transactions put
> into the table. But that is not the question here. If the COPY blocks
> until the ALTER completes --- as it must --- why is its execution snapshot
> not taken *after* the lock is acquired?
COPY waits in DoCopy() but its snapshot gets acquired in PortalRunUtility()
earlier. SELECT has it's lock already during transform/analyse phase and
its snapshot is taken much later. Looks like we need something that
analyses a utility statement to get its lock before executing.
--
Thanks
Bernd
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