Re: Scaling shared buffer eviction

Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Sep 4, 2014 at 7:25 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> Its not difficult to handle such cases, but it can have downside also
>> for the cases where demand from backends is not high.
>> Consider in above case if instead of 500 more allocations, it just
>> does 5 more allocations, then bgreclaimer will again have to go through
>> the list and move 5 buffers and same can happen again by the time
>> it moves 5 buffers.
>
> That's exactly the scenario in which we *want* the looping behavior.
> If that's happening, then it means it's taking us exactly as long to
> find 5 buffers as it takes the rest of the system to use 5 buffers.
> We need to run continuously to keep up.

That's what I was thinking, as long as there isn't a lot of
overhead to starting and finishing a cycle. If there is, my
inclination would be to try to fix that rather than to sleep and
hope things don't get out of hand before it wakes up again.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company