Subject: Re: Extremely slow DELETE with cascade foreign keys
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: pgsql-performance@lists.postgresql.org
References: <20171205164328.6t4w3abfpzp54y2y@alvherre.pgsql>
From: Rodrigo Rosenfeld Rosas <rr.rosas@gmail.com>
Message-ID: <3c0737b6-091b-9de4-7d7a-51f78544fc0d@gmail.com>
Date: Tue, 5 Dec 2017 15:22:45 -0200
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Em 05-12-2017 14:43, Alvaro Herrera escreveu:
> Rodrigo Rosenfeld Rosas wrote:
>
>> explain analyze delete from field_values where transaction_id=226;
>> QUERY PLAN
>> ---------------------------------------------------------------------------------------------------------------------------------------------------------------
>>   Delete on field_values  (cost=0.43..257.93 rows=481 width=6) (actual
>> time=367375.805..367375.805 rows=0 loops=1)
>>     ->  Index Scan using index_field_values_on_transaction_id on
>> field_values  (cost=0.43..257.93 rows=481 width=6) (actual time=0.223..4.216
>> rows=651 loops=1)
>>           Index Cond: (transaction_id = 226)
>>   Planning time: 0.234 ms
>>   Execution time: 367375.882 ms
>> (5 registros)
>>
>> Time: 367377,085 ms (06:07,377)
> Normally this is because you lack indexes on the referencing columns, so
> the query that scans the table to find the referencing rows is a
> seqscan.
>

Thank you, Álvaro, that was indeed the case, just like Tom Lane 
suggested as well. I found the missing index and fixed it. Thanks :)