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Re: Using ProcSignal to get memory context stats from a runningbackend - Mailing list pgsql-hackers

From Maksim Milyutin
Subject Re: Using ProcSignal to get memory context stats from a runningbackend
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Msg-id d23870b3-87d3-f733-a57a-20d4f82caa16@gmail.com
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In response to Re: Using ProcSignal to get memory context stats from a running backend  (Craig Ringer <craig@2ndquadrant.com>)
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On 27.12.2017 10:44, Craig Ringer wrote:

On 22 December 2017 at 23:19, Maksim Milyutin <milyutinma@gmail.com> wrote:
Noticing the interest in the calling some routines on the remote backend through signals, in parallel thread[1] I have proposed the possibility to define user defined signal handlers in extensions. There is a patch taken from pg_query_state module.

1. https://www.postgresql.org/message-id/3f905f10-cf7a-d4e0-64a1-7fd9b8351592%40gmail.com


Haven't read the patch, but the idea seems useful if a bit hairy in practice. It'd be done on a "use at your own risk, and if it breaks you get to keep the pieces" basis, where no guarantees are made by Pg about how and when the function is called so it must be utterly defensive. The challenge there being that you can't always learn enough about the state of the system without doing things that might break it, so lots of things you could do would be fragile.

Yes, I agree with your thesis that the state of the system have to be checked/rechecked before starting its manipulation in signal handler. And the responsibility is down to developer of extension to provide the necessary level of defensive. Perhaps, it makes sense to add try-catch block around signal handler to interrupt potential errors therefrom.

-- 
Regards,
Maksim Milyutindefe

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