Re: Optional message to user when terminating/cancelling backend

2017-06-19 20:24 GMT+02:00 Daniel Gustafsson <daniel(at)yesql(dot)se>:

> When terminating, or cancelling, a backend it’s currently not possible to
> let
> the signalled session know *why* it was dropped. This has nagged me in the
> past and now it happened to come up again, so I took a stab at this. The
> attached patch implements the ability to pass an optional text message to
> the
> signalled session which is included in the error message:
>
> SELECT pg_terminate_backend(<pid> [, message]);
> SELECT pg_cancel_backend(<pid> [, message]);
>
> Right now the message is simply appended on the error message, not sure if
> errdetail or errhint would be better? Calling:
>
> select pg_terminate_backend(<pid>, 'server rebooting');
>
> ..leads to:
>
> FATAL: terminating connection due to administrator command: "server
> rebooting"
>
> Omitting the message invokes the command just like today.
>
> The message is stored in a new shmem area which is checked when the
> session is
> aborted. To keep things simple a small buffer is kept per backend for the
> message. If deemed too costly, keeping a central buffer from which slabs
> are
> allocated can be done (but seemed rather complicated for little gain
> compared
> to the quite moderate memory spend.)
>
> cheers ./daniel
>

+1

very good idea

Pavel

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