Re: Query hitting empty tables taking 48 minutes

On 06/07/2018 11:17 AM, Robert Creager wrote:
>
> I have a system running FreeBSD 11.1-STABLE, PostgreSQL 9.6.8,Java
> OpenJDK 1.8.0_131, jdbc 9.3-1104-jdbc41 which is exhibiting very bizarre
> behavior.  A query is executing against a couple of tables that have 1
> and 0 records in them.  ds3.job_entry has 0 rows, ds3.blob has 1 row.
>  If I execute the query manually via command line, it executes fine.
>  There are no other active queries, no locks.  The system is idle, in
> our Dev Test group, so I can leave it this way for a bit of time.  The
> general software setup is in production and I’ve seen nothing like this
> before.  Even a system with 300M ds3.blob entries executes this query fine.

So I am assuming the problem query is being run through Java/jdbc, correct?

There is also the below in the log:

" ... execute fetch from S_2037436/C_2037437 ..."

My guess is that we will need to see the Java code that sets up and runs
the query. Is that possible?

>
> Jun  7 17:24:21 blackpearl postgres[10670]: [7737-1]
> db=tapesystem,user=Administrator,app=[unknown],client=127.0.0.1
> LOG:  duration: *2903612.206* ms  execute fetch
> from S_2037436/C_2037437: SELECT * FROM ds3.blob WHERE EXISTS (SELECT *
> FROM ds3.job_entry WHERE blob_id = ds3.blob.id <http://ds3.blob.id> AND
> (job_id = $1))
>
> tapesystem=# explain analyze SELECT * FROM ds3.blob WHERE EXISTS (SELECT
> * FROM ds3.job_entry WHERE blob_id = ds3.blob.id <http://ds3.blob.id>
> AND (job_id = 'b51357cd-e07a-4c87-a50b-999c347a5c71'));
>                                                               QUERY PLAN
> ---------------------------------------------------------------------------------------------------------------------------------------
>
>  Nested Loop  (cost=0.84..6.89 rows=1 width=77) (actual
> time=0.044..0.044 rows=0 loops=1)
>    ->  Index Scan using job_entry_job_id_idx on
> job_entry  (cost=0.42..2.44 rows=1 width=16) (actual time=0.042..0.042
> rows=0 loops=1)
>          Index Cond: (job_id =
> 'b51357cd-e07a-4c87-a50b-999c347a5c71'::uuid)
>    ->  Index Scan using blob_pkey on blob  (cost=0.42..4.44 rows=1
> width=77) (never executed)
>          Index Cond: (id = job_entry.blob_id)
>  Planning time: 0.388 ms
>  Execution time: 0.118 ms
>
>
> pid client_port runtime query_start datname state query usename
> 10670 11211 0 years 0 mons 0 days 0 hours 43 mins 28.852273 secs
> 2018-06-07 17:24:22.026384 tapesystem active SELECT * FROM ds3.blob
> WHERE EXISTS (SELECT * FROM ds3.job_entry WHERE blob_id = ds3.blob.id
> <http://ds3.blob.id> AND (job_id = $1)) Administrator
>
>
>
> From the system with 300M ds3.blob entries, which works fine (along
> with every other system in house):
>
> QUERY PLAN
> Nested Loop  (cost=0.57..738052.90 rows=164379 width=75) (actual
> time=1.001..1947.029 rows=50000 loops=1)
>   ->  Seq Scan on job_entry  (cost=0.00..10039.50 rows=164379 width=16)
> (actual time=0.871..56.442 rows=50000 loops=1)
>         Filter: (job_id = 'ef27d2fa-2727-424e-8f44-da9e33a5ca05'::uuid)
>         Rows Removed by Filter: 60001
>   ->  Index Scan using blob_pkey on blob  (cost=0.57..4.42 rows=1
> width=75) (actual time=0.037..0.037 rows=1 loops=50000)
>         Index Cond: (id = job_entry.blob_id)
> Planning time: 6.330 ms
> Execution time: 1951.564 ms
>
>
> Please keep my CC of my work e-mail present.
>
> Best,
> Robert

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com