Re: less expensive pg_buffercache on big shmem

On 09/02/2016 11:01 AM, Robert Haas wrote:
> On Fri, Sep 2, 2016 at 8:49 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> On 2016-09-02 08:31:42 +0530, Robert Haas wrote:
>>> I wonder whether we ought to just switch from the consistent method to
>>> the semiconsistent method and call it good.
>>
>> +1. I think, before long, we're going to have to switch away from having
>> locks & partitions in the first place. So I don't see a problem relaxing
>> this. It's not like that consistency really buys you anything... I'd
>> even consider not using any locks.
>
> I think we certainly want to lock the buffer header, because otherwise
> we might get a torn read of the buffer tag, which doesn't seem good.
> But it's not obvious to me that there's any point in taking the lock
> on the buffer mapping partition; I'm thinking that doesn't really do
> anything unless we lock them all, and we all seem to agree that's
> going too far.

+1 from me to only locking the buffer headers. IMHO that's perfectly
fine for the purpose of this extension.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services