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(dot)klaver(at)aklaver(dot)com