Re: Unexpected "canceling statement due to user request" error

On 8/16/19 2:02 PM, Will Storey wrote:
> Hi!
> 
> I have a query that fails due to this error and I'm trying to understand
> why.
> 
> My understanding is I should only see this error if I cancel a query
> manually, such as with kill -INT or with pg_cancel_backend(). However I
> can't find anything doing that.
> 
> The query looks like this:
> 
>      SELECT *
>      FROM (
>        SELECT
>          c1, c2, [...],
>          EXTRACT(EPOCH FROM time) AS epoch,
>          to_rfc3339_us(time) AS time_rfc3339
>        FROM t1
>        WHERE
>          NOT EXISTS (SELECT 1 FROM t2 WHERE c2 = ?) AND
>          c2 = ? AND
>          time < ? AND
>          time > ?::timestamptz - ? * interval '1 day'
>        LIMIT ?
>      ) AS s
>      ORDER BY epoch DESC
> 
> t1 is partitioned on time, by month.
> 
> I run it using Perl's DBI with DBD::Pg. I wrap it in a transaction where I
> first run:
> 
>      SET LOCAL statement_timeout TO 1000
> 
> I know this query can time out, and it does, resulting in the error I
> expect: "canceling statement due to statement timeout". The problem is
> occasionally I see this other error: "canceling statement due to user
> request".
> 
> Looking at the query logs, when the query fails with the user request
> error, the query reached the statement timeout (at least in cases I
> checked). In one instance the duration shows as 1283ms for example.
> 
> Could there be any situation where a query getting cancelled due to a
> statement timeout be reported as cancelled due to user request? Or do you
> have any ideas about what might be going on?

Here is the relevant source:

https://doxygen.postgresql.org/postgres_8c.html#ab7af3ee6ad40efb8454c6f2f790d9588

Start at around line 3078.

> 
> This is on PostgreSQL 9.6.14 on Ubuntu Xenial.
> 
> Thank you!
> 
> 
> 


-- 
Adrian Klaver
adrian.klaver@aklaver.com