Re: Synchronized Scan WIP patch

Will use '16' rather than '100'.

Your patch has been added to the PostgreSQL unapplied patches list at:

    http://momjian.postgresql.org/cgi-bin/pgpatches

It will be applied as soon as one of the PostgreSQL committers reviews
and approves it.

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Jeff Davis wrote:
> This is my latest revision of the Sync Scan patch, and it implements the
> observability as discussed with Simon.
>
> Changes:
>  * ss_report_loc() called once per hundred pages rather than once per
> page
>  * DEBUG messages are a little cleaner and easier to parse, for the sake
> of analysis after the fact.
>  * DEBUG2 reports a sync scan starting, the relation size in pages, and
> the location at which the scan starts.
>  * DEBUG2 reports the location of a scan every 50k pages, DEBUG3 every
> 5k pages (before it was 100k/10k at DEBUG3/DEBUG4, respectively).
> Numbers are aligned along 5k boundaries to make analysis easier.
>  * GUCs:
>    * sync_seqscan_threshold: fraction of NBuffers for the threshold
>    * sync_seqscan_offset: fraction of NBuffers for the offset
>    * trace_sync_seqscan: will be used in final version of patch to
> control DEBUG output
>
> Sync_scan_offset may be eliminated completely if it's not shown to be
> useful enough in conjunction with Simon's patch. Sync Scans are still a
> big win without sync_seqscan_offset.
>
> Sync_scan_threshold=<real> may be turned into sync_seqscan=<boolean>
> with a fixed activation threshold (NBuffers/2 per Simon's suggestion).
> The reason is that synchronized scans should activate at the same
> threshold as Simon's scan_recycle_buffers feature. Should we make a
> "#define BIG_SCAN_THRESHOLD NBuffers/2" to use for both sync_seqscan and
> for scan_recycle_buffers?
>
> Regards,
>     Jeff Davis

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  Bruce Momjian  <bruce@momjian.us>          http://momjian.us
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