Kevin,
Perhaps I can cause the same situation (maybe tomorrow when the server
isn't occupied) and give this a try. But I think I have already ruled
this out as an option. When I would hit ctrl+c in the psql terminal,
I'd see a message that the query was being cancelled...then it would
just sit there and continue grinding away - unless there's a possibility
that maybe the ctrl+c command didn't actually reach the postgres
process, my guess is that maybe the attempt to rollback gracefully is
just as intensive.
Mike
Kevin Neufeld wrote:
Paul, while "kill -9" will undoubtedly stop the current running query,
it will also crash the entire database cluster since the shared memory
will become corrupt.
I recommend using a "kill -2" instead which is the same thing as issuing
a ctrl^c while in the terminal program. It may take longer since it has
to rollback the transaction, but it will do so gracefully.
-- Kevin
Paul Ramsey wrote:
Break yourself of the subquery habit:
select a.* from a join b on (st_dwithin(a.the_geom,b.the_geom,50000))
where b.gid = 10;
On your process:
ps ax | grep postgres
Find the process id that is using all the CPU and just kill -9 it. The
glory of running a proper ACID database like PgSQL is that if you
don't like what it's doing, you can rip the power cord out of the
wall, and it'll still start up clean. (Do not try this with MySQL.)
P.
buffer((select b.the_geom
where gid = 10),50000));
On Mon, Jul 14, 2008 at 4:33 PM, Mike Leahy <mgleahy at alumni.uwaterloo.ca>
wrote:
Hello list,
I've run into some situations where running certain queries end up locking
up all of my system's ram memory, with constant disk access. I can't cancel
the query by hitting ctrl+c in the psql terminal, by restarting the service,
or even killing the postmaster. I'm running on a fairly high end system, so
it's not an issue with CPU power or available ram. Here's an example of
what I did today that caused this:
Table A is a table I imported from a tile index shapefile.
Table B has several fairly large irregular polygons of different study
areas.
To get all of the polygons in Table A within a certain distance (50km) of
one of the polygons in Table B, without giving it much thought I did the
following:
select * from a where st_intersects(a.the_geom,buffer((select b.the_geom
where gid = 10),50000));
I realize how wrong that is, as calculates the buffer for every tile it
compares to...I should have done something like:
select * from a where st_intersects(a.the_geom,(select b.the_geom where gid
= 10)) or st_distance(a.the_geom,(select b.the_geom where gid = 10))<=50000;
The problem is...I'm still waiting for the first query to either finish, or
cancel, or something. In the meantime, postmaster is still using 99% of my
memory, and the disk is still thrashing away (though CPU usage pretty much
at 0). What's the best strategy to kill the previous query without having
to shut down the entire server?
Keep in mind that is just an example of how this can happen for me - I've
had it happen in other more complex situations where it was less obvious
what I was doing wrong in the logic of the query. I'm just wondering how I
can recover from these sorts of mistakes without potentially damaging the
database.
Regards,
Mike
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