Re: [HACKERS] Autovacuum launcher occurs error when cancelled by SIGINT

On Wed, Jun 21, 2017 at 5:45 PM, Yugo Nagata <nagata@sraoss.co.jp> wrote:
> Hi,
>
> As I report in another thread[1], I found the autovacuum launcher occurs
> the following error in PG 10 when this received SIGINT. I can repuroduce
> this by pg_cancel_backend or `kill -2 <pid of autovacuum laucher>`.
>
> 2017-06-21 13:56:07.010 JST [32483] ERROR:  canceling statement due to user request
> 2017-06-21 13:56:08.022 JST [32483] ERROR:  can't attach the same segment more than once
> 2017-06-21 13:56:09.034 JST [32483] ERROR:  can't attach the same segment more than once
> 2017-06-21 13:56:10.045 JST [32483] ERROR:  can't attach the same segment more than once
> ...
>
> This errors continue until this process is terminated or the server is restarted.
>
> When SIGINT is issued, the process exits from the main loop and returns
> to sigsetjmp, and calls dsa_attach() before entering into the loop again,
> this causes the error.
>
> We can fix it by calling dsa_attach() before sigsetjmp. Attached is the patch.
>
I think we can just check dsm_find_mapping() to check whether the dsm
handle is already attached. Something like,
       }
-       else
+       else if(!dsm_find_mapping(AutoVacuumShmem->av_dsa_handle))       {               AutoVacuumDSA =
dsa_attach(AutoVacuumShmem->av_dsa_handle);              dsa_pin_mapping(AutoVacuumDSA);
 

Thoughts?

-- 
Thanks & Regards,
Kuntal Ghosh
EnterpriseDB: http://www.enterprisedb.com