Re: Postmaster Crashing - Postgres 11 when JIT is enabled

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От Mukesh Chhatani
Тема Re: Postmaster Crashing - Postgres 11 when JIT is enabled
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Msg-id CACnmOYLSxyDqAJ45oxC5cbfqsyZrKosxWQD3t6bGSfm8if92XA@mail.gmail.com
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Ответ на Re: Postmaster Crashing - Postgres 11 when JIT is enabled  (Andres Freund <andres@anarazel.de>)
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Thanks for responding to my query.

I have simultaneously opened a bug with AWS too.

Issue happens with large tables (size > 5 GB) and is consistent across multiple databases. It does not happen when JIT is disabled or max_parallel_workers_per_gather = 0 is used in a session.

I am not running the query just starting it and then cancelling in between - using Control + C, which causes postmaster to crash.

Here is the table definition

Column        |           Type           | Collation | Nullable | Default | Storage  | Stats target | Description
---------------------+--------------------------+-----------+----------+---------+----------+--------------+-------------
 id                  | text                     |           | not null |         | extended |              |
 event               | text                     |           | not null |         | extended |              |
 unique_id           | uuid                     |           | not null |         | plain    |              |
 surgate_id          | text                     |           |          |         | extended |              |
 user_agent          | text                     |           |          |         | extended |              |
 code                | text                     |           |          |         | extended |              |
 encrypted.          | text                     |           |          |         | extended |              |
 hash                | text                     |           |          |         | extended |              |
 start_time          | timestamp with time zone |           | not null |         | plain    |              |
 expected_expiration | timestamp with time zone |           |          |         | plain    |              |
 end_time            | timestamp with time zone |           |          |         | plain    |              |
 level               | text                     |           |          |         | extended |              |
Indexes:

    "sessions_pkey" PRIMARY KEY, btree (id)
    "id_date" btree (unique_id, expected_expiration)
    "sessions_rid" btree (unique_id)
    "sessions_surrogate_id" btree (surgate_id)


Thanks & Regards,

Mukesh

On Tue, Jun 9, 2020 at 2:11 PM Andres Freund <andres@anarazel.de> wrote:
Hi,

On 2020-06-09 14:00:06 -0500, Mukesh Chhatani wrote:
> We are experiencing issues around Postmaster crashing due to cancellation
> of a simple query
>
> Postgres Version - 11.6
> Environment - AWS RDS
> Table Size - 50 GB

Unfortunately we do not have access to the exact changes RDS has done to
postgres, so we cannot easily debug such problems.


> Few ways I resolved the issue :
> 1. Vacuum analyze the table and then execute the query and cancel it.
> 2. Disable JIT
> 3. Set max_parallel_workers_per_gather = 0
>
> Attached is the file containing DEBUG logs and ERROR we are experiencing
> issues with.

I am afraid that we need more information to be able to debug this
problem. The best would be a backtrace of the crash, but for that you'd
likely need help from RDS support.

Can you post the exact table definition of the table with the problem?
And an EXPLAIN for the problematic query?


Are you saying that after
> 1. Vacuum analyze the table and then execute the query and cancel it.

the problem does not occur anymore for future queries?

Greetings,

Andres Freund

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