On 12 September 2014 14:54, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> My idea is that we would have a new executor flag, say
> EXEC_FLAG_READ_ONLY; we would set it on nodes that are known to be
> read-only, and reset it on those that aren't, such as LockRows and
> ModifyTable (obviously we need to pass it down correctly from parent to
> children). Then in ExecInitSeqScan and ExecInitIndexScan, if we see the
> flag set, we call heap/index_set_allow_prune(false) for the heap scan;
> same thing in index scans. (I envisioned it as a boolean rather than
> enabling a certain number of cleanups per scan.)
>
> I tried to code this but I think it doesn't work correctly, and no time
> for debug currently. Anyway let me know what you think of this general
> idea.
Thanks for looking at this.
My concern was to ensure that UPDATEs and DELETEs continue to call
heap_page_prune_opt while larger SELECTs do not.
This is achieved without a counter, so after some thought like it
better; simple is good. Happy to progress from here, or you can?
-- Simon Riggs http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services