| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Magnus Hagander <magnus(at)hagander(dot)net>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Merlin Moncure <mmoncure(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: proposal: Set effective_cache_size to greater of .conf value, shared_buffers |
| Date: | 2014-05-07 13:50:41 |
| Message-ID: | CA+U5nMLR+L0-tvZ=SM=brrVW84GfZeCUjF4AxhZA-B9_cNacug@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 7 May 2014 13:31, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Wed, May 7, 2014 at 3:18 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> If we believe that 25% of shared_buffers worth of heap blocks would
>> flush the cache doing a SeqScan, why should we allow 400% of
>> shared_buffers worth of index blocks?
>
> I think you're comparing apples and oranges.
I understood the distinction, which is why I changed the direction of
my thinking to say
> Yes, we can make plans assuming we can use OS cache,
> but we shouldn't be churning shared_buffers when we execute those
> plans.
and hence why I proposed
> I think I'm arguing myself towards using a BufferAccessStrategy of
> BAS_BULKREAD for large IndexScans, BitMapIndexScans and
> BitMapHeapScans.
which I hope will be effective in avoiding churn in shared_buffers
even though we may use much larger memory from the OS.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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