Re: On-demand running query plans using auto_explain and signals

On Fri, Sep 25, 2015 at 7:13 PM, Shulgin, Oleksandr <
oleksandr(dot)shulgin(at)zalando(dot)de> wrote:

>
> Some implementation details:
>
> For every backend that might be running (MaxBackends) we reserve a
> dsm_handle slot in the addins shared memory. When the new option is turned
> on, the ExecutorRun hook will produce a plan in whatever format is
> specified by the auto_explain.log_format, allocate a DSM segment, copy the
> plan into the segment and finally store the DSM handle into its own slot.
> No locking is required around this because every backend writes to its slot
> exclusively, no other backend can be writing into it concurrently. In the
> ExecutorFinish hook we invalidate the backend's slot by setting the handle
> to 0 and deallocate the DSM segment.
>

And this patch adds back the use of table of contents on the DSM.
Benefits: magic number validation; communication of the actual plan size.

--
Alex