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Is it normal for a query to spawn three query processes?

I have a rails application and am trying to troubleshoot some database performance issues, and I just noticed, when I make a query from the rails console:

MyModel.where("field ILIKE '%hello%'")

when I look at postgres for active queries:

SELECT pid, age(clock_timestamp(), query_start), usename, query FROM pg_stat_activity WHERE state != 'idle' AND query NOT ILIKE '%pg_stat_activity%';

I am seeing:

 28877 | 00:00:00.868747 | me | SELECT "shares".* FROM "shares" WHERE (message ilike '%hello%')
 28960 | 00:00:00.868757 | me | SELECT "shares".* FROM "shares" WHERE (message ilike '%hello%')
 28961 | 00:00:00.868759 | me | SELECT "shares".* FROM "shares" WHERE (message ilike '%hello%')
(3 rows)

I was very concerned that one command is spawning 3 processes??? Is this normal?

Solution

  • Look at the backend_type column of pg_stat_activity, and you will probably see that two of these processes are parallel workers. You are seeing parallel query in action.