From: Sheena, Prabhjot [mailto:prabhjot.si...@classmates.com]
Sent: Friday, June 05, 2015 2:38 PM
To: Igor Neyman; pgsql-gene...@postgresql.org; pgsql-performance@postgresql.org
Subject: RE: Query running slow for only one specific id. (Postgres 9.3) version
When I run vacuum analyze it fixes the problem but after 1 or 2 days the
problem comes back
Here is the table structure
Column | Type |
Modifiers | Storage | Stats target | Description
------------------+-----------------------------+----------------------------------------------------------------------+---------+--------------+-------------
response_id | integer | not null default
nextval('btdt_responses_response_id_seq'::regclass) | plain | |
registration_id | bigint | not null
| plain | |
btdt_id | integer | not null
| plain | |
response | integer | not null
| plain | |
creation_date | timestamp without time zone | not null default now()
| plain | |
last_update_date | timestamp without time zone | not null default now()
| plain | |
Indexes:
"btdt_responses_pkey" PRIMARY KEY, btree (response_id)
"btdt_responses_u2" UNIQUE, btree (registration_id, btdt_id)
"btdt_responses_n1" btree (btdt_id)
"btdt_responses_n2" btree (btdt_id, response)
"btdt_responses_n4" btree (creation_date)
"btdt_responses_n5" btree (last_update_date)
"btdt_responses_n6" btree (btdt_id, last_update_date)
Foreign-key constraints:
"btdt_responses_btdt_id_fkey" FOREIGN KEY (btdt_id) REFERENCES
btdt_items(btdt_id)
"btdt_responses_fk1" FOREIGN KEY (btdt_id) REFERENCES btdt_items(btdt_id)
Has OIDs: no
Options: autovacuum_enabled=true, autovacuum_vacuum_scale_factor=0.02,
autovacuum_analyze_scale_factor=0.02
Thanks
From: Igor Neyman [mailto:iney...@perceptron.com]
Sent: Friday, June 5, 2015 11:06 AM
To: Sheena, Prabhjot;
pgsql-gene...@postgresql.org<mailto:pgsql-gene...@postgresql.org>;
pgsql-performance@postgresql.org<mailto:pgsql-performance@postgresql.org>
Subject: RE: Query running slow for only one specific id. (Postgres 9.3) version
From:
pgsql-performance-ow...@postgresql.org<mailto:pgsql-performance-ow...@postgresql.org>
[mailto:pgsql-performance-ow...@postgresql.org] On Behalf Of Sheena, Prabhjot
Sent: Friday, June 05, 2015 1:55 PM
To: pgsql-gene...@postgresql.org<mailto:pgsql-gene...@postgresql.org>;
pgsql-performance@postgresql.org<mailto:pgsql-performance@postgresql.org>
Subject: [PERFORM] Query running slow for only one specific id. (Postgres 9.3)
version
Postgresql 9.3 Version
Guys
Here is the issue that I'm facing for couple of weeks now. I have
table (size 7GB)
If I run this query with this specific registration id it is using the wrong
execution plan and takes more than a minute to complete. Total number of rows
for this registration_id is only 414 in this table
explain analyze SELECT max(last_update_date) AS last_update_date FROM
btdt_responses WHERE registration_id = 8718704208 AND response != 4;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Result (cost=2902.98..2903.01 rows=1 width=0) (actual
time=86910.730..86910.731 rows=1 loops=1)
InitPlan 1 (returns $0)
-> Limit (cost=0.57..2902.98 rows=1 width=8) (actual
time=86910.725..86910.725 rows=1 loops=1)
-> Index Scan Backward using btdt_responses_n5 on btdt_responses
(cost=0.57..6425932.41 rows=2214 width=8) (actual time=86910.723..86910.723
rows=1 loops=1)
Index Cond: (last_update_date IS NOT NULL)
Filter: ((response <> 4) AND (registration_id =
8718704208::bigint))
Rows Removed by Filter: 52145434
Total runtime: 86910.766 ms
Same query with any other registration id will come back in milli seconds
explain analyze SELECT max(last_update_date) AS last_update_date FROM
btdt_responses WHERE registration_id = 8688546267 AND response != 4;
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=529.75..529.78 rows=1 width=8) (actual time=19.723..19.723
rows=1 loops=1)
-> Index Scan using btdt_responses_u2 on btdt_responses (cost=0.57..529.45
rows=119 width=8) (actual time=0.097..19.689 rows=72 loops=1)
Index Cond: (registration_id = 8688546267::bigint)
Filter: (response <> 4)
Rows Removed by Filter: 22
Total runtime: 19.769 ms
Please let me know what I can do to fix this issue.
Thanks
Not enough info.
Table structure? Is registration_id - PK? If not, what is the distribution of
the values for this table?
When was it analyzed last time? M.b. you need to increase statistics target
for this table:
Index Scan Backward using btdt_responses_n5 on btdt_responses
(cost=0.57..6425932.41 rows=2214 width=8) (actual time=86910.723..86910.723
rows=1 loops=1)
It expects 2214 records while really getting only 1.
Regards,
Igor Neyman
Do you have autovacuum running?
If yes, maybe it's not aggressive enough and you need to adjust its parameters.
Regards,
Igor Neyman
