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Thread: Possible bug in new VACUUM code

Possible bug in new VACUUM code

From
Jan Wieck
Date:
Hi,
   I  just stumbled over a very hard to reproduce error. Running   a "VACUUM ANALYZE <table>" concurrently to a
database heavy   under  load  caused a SELECT ... FOR UPDATE with full primary   key qualification to return multiple
resultsfrom that table.   The  table  contains  only  a few rows which receive ton's of   updates.
 
   System is 7.2B3 under Linux.
   Will try to produce a test case, just to let ppl know  early.


Jan

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Re: Possible bug in new VACUUM code

From
Tom Lane
Date:
Jan Wieck <janwieck@yahoo.com> writes:
>     I  just stumbled over a very hard to reproduce error. Running
>     a "VACUUM ANALYZE <table>" concurrently to a  database  heavy
>     under  load  caused a SELECT ... FOR UPDATE with full primary
>     key qualification to return multiple results from that table.

Urgh.  But I am not sure that you should be pointing the finger at
VACUUM.  It doesn't move any tuples around (at least not in ctid
terms), so how could it possibly produce multiple tuple images in
another scan?  My early bet is that the problem is not directly
related to VACUUM.

Post as soon as you have any more info ... remember there are lots
of eyeballs out here ...
        regards, tom lane

Re: Possible bug in new VACUUM code

From
mlw
Date:
Jan Wieck wrote:
> 
> Hi,
> 
>     I  just stumbled over a very hard to reproduce error. Running
>     a "VACUUM ANALYZE <table>" concurrently to a  database  heavy
>     under  load  caused a SELECT ... FOR UPDATE with full primary
>     key qualification to return multiple results from that table.
>     The  table  contains  only  a few rows which receive ton's of
>     updates.
> 
>     System is 7.2B3 under Linux.
> 
>     Will try to produce a test case, just to let ppl know  early.

Can you post an explain plan for the query along with a "\d" of the table?