Re: Slow query in JDBC

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If I run the below commands from psql command line then in the explain output it showing as its using the index.

prepare foo as <your query>
explain execute foo;

But if I run the same query from my application using JDBC PreparedStatement then it showing as its doing sequence scan.

To which version should I upgrade my JDBC driver? Will it help resolving this issue?

Please help.

Thanks and Regards
Subramaniam

On Fri, Sep 29, 2017 at 12:34 AM, Dave Cramer <pg@xxxxxxxxxxxxx> wrote:
Why are you using such an old version of the driver ?

Either way the driver is going to use prepare statement to run this, that is the difference from it an psql.


If you want to see the explain in psql you will need to do 

prepare foo as <your query>

then explain execute foo;

FWIW upgrading the driver won't help this situation but there's still no reason not to upgrade.


On 28 September 2017 at 12:32, Subramaniam C <subramaniam31784@xxxxxxxxx> wrote:
The JDBC version is 9.4-1201-jdbc41.

Query :-

select count(*) OVER() AS count,uuid,availability,objectname,datasourcename,datasourcetype,objecttype,health from (select distinct on (health_timeseries_table.mobid) mobid, health_timeseries_table.health, health_timeseries_table.timestamp from health_timeseries_table where timestamp >= 1505989186834 and timestamp <= 1505990086834 ORDER BY health_timeseries_table.mobid DESC, health_timeseries_table.timestamp DESC, health_timeseries_table.health ASC) t right join (SELECT DISTINCT ON (object_table.uuid) uuid, object_table.timestamp,object_table.availability,object_table.objectname,object_table.datasourcename,object_table.datasourcetype,object_table.objecttype FROM object_table where  object_table.timestamp >= 0 and object_table.timestamp <= 1505990086834 and object_table.tenantid = 'perspica' ORDER BY object_table.uuid DESC, object_table.timestamp DESC)u on (t.mobid = u.uuid) order by health asc limit 20 offset 0;


Please let us know any other details?


Thanks and Regards

Subramaniam


On Thu, Sep 28, 2017 at 7:29 PM, Dave Cramer <pg@xxxxxxxxxxxxx> wrote:
What version of the driver are you using?

The driver does not automatically use a cursor, but it does use prepared statements which can be slower.


Can you provide the query and the jdbc query ?




On 28 September 2017 at 05:59, Subramaniam C <subramaniam31784@xxxxxxxxx> wrote:
First output show the output when the query is executed from sql command line. The second output show when it is executed from the application. AS per the output it is clear that the when the query is executed through JDBC its not using the index (health_index) instead its doing sequence scan. Please let us know how this issue can be resolved from JDBC?

1.)


Limit  (cost=510711.53..510711.58 rows=20 width=72)

  ->  Sort  (cost=510711.53..511961.53 rows=500000 width=72)

        Sort Key: health_timeseries_table.health

        ->  WindowAgg  (cost=0.98..497406.71 rows=500000 width=72)

              ->  Merge Left Join  (cost=0.98..491156.71 rows=500000 width=64)

                    Merge Cond: (object_table.uuid = health_timeseries_table.mobid)

                    ->  Unique  (cost=0.42..57977.00 rows=500000 width=64)

                          ->  Index Scan Backward using object_table_pkey on object_table  (cost=0.42..56727.00 rows=500000 width=64)

                                Index Cond: (("timestamp" >= 0) AND ("timestamp" <= '1505990086834'::bigint))

                                Filter: (tenantid = 'perspica'::text)

                    ->  Materialize  (cost=0.56..426235.64 rows=55526 width=16)

                          ->  Unique  (cost=0.56..425541.56 rows=55526 width=24)

                                ->  Index Only Scan using health_index on health_timeseries_table  (cost=0.56..421644.56 rows=1558800 width=24)

                                      Index Cond: (("timestamp" >= '1505989186834'::bigint) AND ("timestamp" <= '1505990086834'::bigint))

LOG:  duration: 1971.697 ms





2.)


Limit  (cost=457629.21..457629.26 rows=20 width=72)

  ->  Sort  (cost=457629.21..458879.21 rows=500000 width=72)

        Sort Key: health_timeseries_table.health

        ->  WindowAgg  (cost=367431.49..444324.39 rows=500000 width=72)

              ->  Merge Left Join  (cost=367431.49..438074.39 rows=500000 width=64)

                    Merge Cond: (object_table.uuid = health_timeseries_table.mobid)

                    ->  Unique  (cost=0.42..57977.00 rows=500000 width=64)

                          ->  Index Scan Backward using object_table_pkey on object_table  (cost=0.42..56727.00 rows=500000 width=64)

                                Index Cond: (("timestamp" >= '0'::bigint) AND ("timestamp" <= '1505990400000'::bigint))

                                Filter: (tenantid = 'perspica'::text)

                    ->  Materialize  (cost=367431.07..373153.32 rows=55526 width=16)

                          ->  Unique  (cost=367431.07..372459.24 rows=55526 width=24)

                                ->  Sort  (cost=367431.07..369945.16 rows=1005634 width=24)

                                      Sort Key: health_timeseries_table.mobid DESC, health_timeseries_table."timestamp" DESC, health_timeseries_table.health

                                      ->  Seq Scan on health_timeseries_table  (cost=0.00..267171.00 rows=1005634 width=24)


                                            Filter: (("timestamp" >= '1505989500000'::bigint) AND ("timestamp" <= '1505990400000'::bigint))


On Thu, Sep 28, 2017 at 2:56 PM, Pavy Philippe <Philippe.Pavy@xxxxxxxxxxxxx> wrote:
https://www.postgresql.org/docs/current/static/auto-explain.html


-----Message d'origine-----
De : pgsql-performance-owner@postgresql.org [mailto:pgsql-performance-owner@xxxxxxxxxxxxxx] De la part de Julien Rouhaud
Envoyé : jeudi 28 septembre 2017 11:21
À : Subramaniam C
Cc : pgsql-performance@postgresql.org
Objet : Re: Slow query in JDBC

On Thu, Sep 28, 2017 at 10:58 AM, Subramaniam C <subramaniam31784@xxxxxxxxx> wrote:
> I configured cursor_tuple_fraction to 1 but still I am facing the same
> issue.

Can you show explain (analyze, buffers) of the query when run from psql and run from application (you can use auto_explain for that if needed, see https://www.postgresql.org/docs/current/static/auto-explain.html).


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