Re: updating statistics on slow running query - Mailing list pgsql-performance

2014-11-10 18:43 GMT+01:00 Eric Ramirez <eric.ramirez.sv@gmail.com>:

Hi,
I have created a sample database with test data to help benchmark our application. The database has ten million records, and is running on a dedicated server(postgres 9.3) with 8GB of RAM.  Our queries are pretty slow with this amount of data and is my job to get them to run to at acceptable speed. First thing that I notice was that the planner's row estimates are off by a large number or records (millions) I have updated the statistics target but didn't seem to make a difference. The relevant output follows.
Am I looking in the wrong place, something else I should be trying?
Thanks in advance for your comments/suggestions,
Eric.


=# show work_mem;
 work_mem
----------
 1GB
(1 row)
=# show effective_cache_size;
 effective_cache_size
----------------------
 5GB
(1 row)

=#ALTER TABLE TAR_MVW_TARGETING_RECORD ALTER COLUMN household_member_first_name SET STATISTICS 5000;
=# vacuum analyse TAR_MVW_TARGETING_RECORD;

=# \d tar_mvw_targeting_record;
             Table "public.tar_mvw_targeting_record"
           Column            |         Type          | Modifiers
-----------------------------+-----------------------+-----------
 household_member_id         | bigint                |
 form_id                     | bigint                |
 status                      | character varying(64) |
 gender                      | character varying(64) |
 household_member_first_name | character varying(64) |
 household_member_last_name  | character varying(64) |

Indexes:
   "tar_mvw_targeting_record_form_id_household_member_id_idx" UNIQUE, btree (form_id, household_member_id)
 "tar_mvw_targeting_record_lower_idx" gist (lower(household_member_first_name::text) extensions.gist_trgm_ops)
 WHERE status::text <> 'ANULLED'::text
    "tar_mvw_targeting_record_lower_idx1" gist (lower(household_member_last_name::text) extensions.gist_trgm_ops)
 WHERE status::text <> 'ANULLED'::text


=# explain (analyse on,buffers on)select T.form_id from TAR_MVW_targeting_record AS T where T.status NOT IN ('ANULLED')  AND LOWER(T.household_member_last_name) LIKE LOWER('%tu%') AND T.gender='FEMALE' group by T.form_id;
                                                                                QUERY PLAN                                                
                              
-------------------------------------------------------------------------------------------------------------------------------------------
-------------------------------
 HashAggregate  (cost=450994.35..452834.96 rows=184061 width=8) (actual time=11932.959..12061.206 rows=442453 loops=1)
   Buffers: shared hit=307404 read=109743
   ->  Bitmap Heap Scan on tar_mvw_targeting_record t  (cost=110866.33..448495.37 rows=999592 width=8) (actual time=3577.301..11629.132 row
s=500373 loops=1)
         Recheck Cond: ((lower((household_member_last_name)::text) ~~ '%tu%'::text) AND ((status)::text <> 'ANULLED'::text))
         Rows Removed by Index Recheck: 9000079
         Filter: ((gender)::text = 'FEMALE'::text)
         Rows Removed by Filter: 499560
         Buffers: shared hit=307404 read=109743
         ->  Bitmap Index Scan on tar_mvw_targeting_record_lower_idx1  (cost=0.00..110616.43 rows=2000002 width=0) (actual time=3471.142..3
471.142 rows=10000012 loops=1)
               Index Cond: (lower((household_member_last_name)::text) ~~ '%tu%'::text)
               Buffers: shared hit=36583 read=82935
 Total runtime: 12092.059 ms
(12 rows)

Time: 12093.107 ms

p.s. this plan was ran three times, first time took 74 seconds.

Hello Eric,

                        did you try with gin index instead ? so you could avoid, if possible, the recheck condition (almost the gin index is not lossy ), further if you always use a predicate like "gender=" , you could think to partition the indexes based on that predicate (where status NOT IN ('ANULLED')  and gender='FEMALE', in the other case it wil be where status NOT IN ('ANULLED')  and gender='MALE' ) . Moreover you could avoid also the "lower" operator and try use directly the ilike , instead of "like".

CREATE INDEX tar_mvw_targeting_record_idx02 ON tar_mvw_targeting_record USING gin (  status gin_trgm_ops) where status NOT IN ('ANULLED')  and gender='FEMALE' ;
CREATE INDEX tar_mvw_targeting_record_idx03 ON tar_mvw_targeting_record USING gin (  status gin_trgm_ops) where status NOT IN ('ANULLED')  and gender='MALE' ;

explain (analyse on,buffers on)  select T.form_id from TAR_MVW_targeting_record AS T where T.status NOT IN ('ANULLED')  AND T.household_member_last_name ilike LOWER('%tu%') AND T.gender='FEMALE' group by T.form_id;

 I hope it works

have a nice day

--

Matteo Durighetto

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