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deadlock in single-row select-for-update + update scenario? How could it happen? - Mailing list pgsql-general

From hubert depesz lubaczewski
Subject deadlock in single-row select-for-update + update scenario? How could it happen?
Date
Msg-id CAKrjmhdN+GhAjNwqfHsOtGp+7YN27zR79m99RcAJMNazt5NJrA@mail.gmail.com
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Responses Re: deadlock in single-row select-for-update + update scenario? How could it happen?  (Adrian Klaver <adrian.klaver@aklaver.com>)
Re: deadlock in single-row select-for-update + update scenario? How could it happen?  (Jeff Janes <jeff.janes@gmail.com>)
Re: deadlock in single-row select-for-update + update scenario? How could it happen?  (John R Pierce <pierce@hogranch.com>)
Re: deadlock in single-row select-for-update + update scenario? How could it happen?  (Alvaro Herrera <alvherre@2ndquadrant.com>)
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I have developer with pg 9.3.5, which is reporing something really strange.

He runs importer, which does, in single transaction:

begin;
select * from table where pkey = <value> limit 1 for update;
update table set ... where pkey = <the same_value>;
commit;

and two backends running the same transaction deadlock.

I checked for duplicated rows with the same pkey value - none are there. And frankly - I'm out of ideas.

What could be wrong in such case?

Detailed logs, with just some obfuscation: https://depesz.privatepaste.com/0594a93459

depesz

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