Re: Slow query with joins

I'd try figuring out if the join is the culprit or the sort is (by
dropping the ORDER BY). work_mem is probably forcing the sort to spill
to disk, and if your drives are rather busy...

You might also get a win if you re-order the joins to people, contacts,
addresses, if you know it will have the same result.

In this case LIMIT won't have any real effect, because you have to go
all the way through with the ORDER BY anyway.

On Wed, Jan 11, 2006 at 08:55:32PM +0100, Bendik Rognlien Johansen wrote:
> Yes,  the rowcount estimates are real, however, it has been a long
> time since the last VACUUM FULL (there is never a good time).
>
> I have clustered the tables, reindexed, analyzed, vacuumed and the
> plan now looks like this:
>
>
> no_people=# explain SELECT r.id AS r_id, r.firstname || ' ' ||
> r.lastname AS r_name, ad.id AS ad_id, ad.type AS ad_type, ad.address
> AS ad_address, ad.postalcode AS ad_postalcode, ad.postalsite AS
> ad_postalsite, ad.priority AS ad_priority, ad.position[0] AS ad_lat,
> ad.position[1] AS ad_lon, ad.uncertainty AS ad_uncertainty, ad.extra
> AS ad_extra, ad.deleted AS ad_deleted, co.id AS co_id, co.type AS
> co_type, co.value AS co_value, co.description AS co_description,
> co.priority AS co_priority, co.visible AS co_visible, co.searchable
> AS co_searchable, co.deleted AS co_deleted FROM people r LEFT OUTER
> JOIN addresses ad ON(r.id = ad.record) LEFT OUTER JOIN contacts co ON
> (r.id = co.record) WHERE NOT r.deleted AND  r.original IS NULL ORDER
> BY r.id;
>                                                         QUERY PLAN
> ------------------------------------------------------------------------
> --------------------------------------------------
> Sort  (cost=182866.49..182943.12 rows=30655 width=587)
>    Sort Key: r.id
>    ->  Nested Loop Left Join  (cost=0.00..170552.10 rows=30655
> width=587)
>          ->  Nested Loop Left Join  (cost=0.00..75054.96 rows=26325
> width=160)
>                ->  Index Scan using people_deleted_original_is_null
> on people r  (cost=0.00..1045.47 rows=23861 width=27)
>                      Filter: ((NOT deleted) AND (original IS NULL))
>                ->  Index Scan using addresses_record_idx on
> addresses ad  (cost=0.00..3.05 rows=4 width=137)
>                      Index Cond: ("outer".id = ad.record)
>          ->  Index Scan using contacts_record_idx on contacts co
> (cost=0.00..3.32 rows=24 width=431)
>                Index Cond: ("outer".id = co.record)
> (10 rows)
>
>
>
>
>
>
> Looks faster, but still very slow. I added limit 1000 and it has been
> running for about 25 minutes now with no output. top shows:
>
>
>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
> 29994 postgres  18   0 95768  78m  68m R 17.0  7.7   0:53.27 postmaster
>
>
>
> which is unusual, I usually get 99.9 %cpu for just about any query,
> which leads me to believe this is disk related.
>
>
>
> postgresql.conf:
> shared_buffers = 8192
> work_mem = 8192
> maintenance_work_mem = 524288
>
>
>
>
> Hardware 2x2.8GHz cpu
> 1GB ram
>
> Could this be an issue related to lack of VACUUM FULL? The tables get
> a lot of updates.
>
>
> Thank you very much so far!
>
>
>
>
> On Jan 11, 2006, at 4:45 PM, Tom Lane wrote:
>
> >Bendik Rognlien Johansen <bendik.johansen@gmail.com> writes:
> >>Has anyone got any tips for speeding up this query? It currently
> >>takes hours to start.
> >
> >Are the rowcount estimates close to reality?  The plan doesn't look
> >unreasonable to me if they are.  It might help to increase work_mem
> >to ensure that the hash tables don't spill to disk.
> >
> >Indexes:
> >     "people_original_is_null" btree (original) WHERE original IS NULL
> >
> >This index seems poorly designed: the actual index entries are dead
> >weight since all of them are necessarily NULL.  You might as well make
> >the index carry something that you frequently test in conjunction with
> >"original IS NULL".  For instance, if this particular query is a
> >common
> >case, you could replace this index with
> >
> >CREATE INDEX people_deleted_original_is_null ON people(deleted)
> >  WHERE original IS NULL;
> >
> >This index is still perfectly usable for queries that only say
> >"original
> >IS NULL", but it can also filter out rows with the wrong value of
> >deleted.  Now, if there are hardly any rows with deleted = true, maybe
> >this won't help much for your problem.  But in any case you ought to
> >consider whether you can make the index entries do something useful.
> >
> >            regards, tom lane
>
>
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--
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461