Re: SELECT INTO large FKyed table is slow

От: Pierre C
Тема: Re: SELECT INTO large FKyed table is slow
Дата: ,
Msg-id: op.vm0055s0eorkce@apollo13
(см: обсуждение, исходный текст)
Ответ на: Re: SELECT INTO large FKyed table is slow  (Mario Splivalo)
Ответы: Re: SELECT INTO large FKyed table is slow  (Mario Splivalo)
Список: pgsql-performance

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SELECT INTO large FKyed table is slow  (Mario Splivalo, )
 Re: SELECT INTO large FKyed table is slow  ("Pierre C", )
  Re: SELECT INTO large FKyed table is slow  (Mario Splivalo, )
   Re: SELECT INTO large FKyed table is slow  ("Pierre C", )
    Re: SELECT INTO large FKyed table is slow  (Mario Splivalo, )
     Re: SELECT INTO large FKyed table is slow  ("Pierre C", )
      Re: SELECT INTO large FKyed table is slow  (Mario Splivalo, )
 Re: SELECT INTO large FKyed table is slow  (Mark Kirkwood, )
  Re: SELECT INTO large FKyed table is slow  (Mario Splivalo, )
   Re: SELECT INTO large FKyed table is slow  ("Pierre C", )
    Re: SELECT INTO large FKyed table is slow  (Mario Splivalo, )
     Re: SELECT INTO large FKyed table is slow  ("Pierre C", )
      Re: SELECT INTO large FKyed table is slow  (Mario Splivalo, )
       Re: SELECT INTO large FKyed table is slow  (Robert Haas, )
    Re: SELECT INTO large FKyed table is slow  (Mark Kirkwood, )
 Re: SELECT INTO large FKyed table is slow  (Mladen Gogala, )
  Re: SELECT INTO large FKyed table is slow  (Mario Splivalo, )
   Re: SELECT INTO large FKyed table is slow  ("Pierre C", )
    Re: SELECT INTO large FKyed table is slow  (Mario Splivalo, )
     Re: SELECT INTO large FKyed table is slow  ("Pierre C", )
 Re: SELECT INTO large FKyed table is slow  ("Joshua D. Drake", )
  Re: SELECT INTO large FKyed table is slow  (Mario Splivalo, )
   Re: SELECT INTO large FKyed table is slow  (Mladen Gogala, )
    Re: SELECT INTO large FKyed table is slow  (Mario Splivalo, )
     Re: SELECT INTO large FKyed table is slow  (Mladen Gogala, )
      Re: SELECT INTO large FKyed table is slow  (Kenneth Marshall, )
       Re: SELECT INTO large FKyed table is slow  (Mladen Gogala, )
      Re: SELECT INTO large FKyed table is slow  ("Kevin Grittner", )
       Re: SELECT INTO large FKyed table is slow  (Mladen Gogala, )
       Re: SELECT INTO large FKyed table is slow  ("Pierre C", )
        Re: SELECT INTO large FKyed table is slow  (Mario Splivalo, )
         Re: SELECT INTO large FKyed table is slow  ("Kevin Grittner", )

> So, I did. I run the whole script in psql, and here is the result for
> the INSERT:
>
> realm_51=# explain analyze INSERT INTO drones_history (2771, drone_id,
> drone_log_notice, drone_temperature, drone_pressure) SELECT * FROM
> tmp_drones_history;
>                                                        QUERY PLAN
>
----------------------------------------------------------------------------------------------------------------------
>   Seq Scan on tmp_drones_history  (cost=0.00..81.60 rows=4160 width=48)
> (actual time=0.008..5.296 rows=5150 loops=1)
>   Trigger for constraint drones_history_fk__drones: time=92.948
> calls=5150
>   Total runtime: 16779.644 ms
> (3 rows)
>
>
> Now, this is only 16 seconds. In this 'batch' I've inserted 5150 rows.
> The batch before, I run that one 'the usual way', it inserted 9922 rows,
> and it took 1 minute and 16 seconds.
>
> I did not, however, enclose the process into begin/end.
>
> So, here are results when I, in psql, first issued BEGIN:
>
> realm_51=# explain analyze INSERT INTO drones_history (2772, drone_id,
> drone_log_notice, drone_temperature, drone_pressure) SELECT * FROM
> tmp_drones_history;
>                                                        QUERY PLAN
>
----------------------------------------------------------------------------------------------------------------------
>   Seq Scan on tmp_drones_history  (cost=0.00..79.56 rows=4056 width=48)
> (actual time=0.008..6.490 rows=5059 loops=1)
>   Trigger for constraint drones_history_fk__drones: time=120.224
> calls=5059
>   Total runtime: 39658.250 ms
> (3 rows)
>
> Time: 39658.906 ms
>
>
>
>     Mario
>

Note that in both cases postgres reports that the FK checks take 92-120
milliseconds... which is a normal time for about 4000 rows.
Inserting 4000 lines with just a few fields like you got should take quite
much less than 1 s...

Where the rest of the time goes, I have no idea. Disk thrashing ? Locks ?
Gremlins ?

- try it on a fresh copy of all your tables (CREATE TABLE, INSERT INTO
SELECT)
- try to put the WAL on a separate physical disk (or do a check with
fsync=off)
- try it on another computer
- try it on another harddisk
- run oprofile on a debug compile of postgres
- it could even be the process title updates (I don't think so but...)
- try a ramdisk tablespace


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