Re: Proposing pg_hibernate

On Wed, Jun 4, 2014 at 2:08 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> On 2014-06-04 10:24:13 +0530, Amit Kapila wrote:
>> On Tue, Jun 3, 2014 at 5:43 PM, Gurjeet Singh <gurjeet(at)singh(dot)im> wrote:
>> > On Tue, Jun 3, 2014 at 7:57 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> > > It seems like it would be best to try to do this at cluster startup
>> > > time, rather than once recovery has reached consistency. Of course,
>> > > that might mean doing it with a single process, which could have its
>> > > own share of problems. But I'm somewhat inclined to think that if
>> > > recovery has already run for a significant period of time, the blocks
>> > > that recovery has brought into shared_buffers are more likely to be
>> > > useful than whatever pg_hibernate would load.
>> >
>> > I am not absolutely sure of the order of execution between recovery
>> > process and the BGWorker, but ...
>> >
>> > For sizeable shared_buffers size, the restoration of the shared
>> > buffers can take several seconds.
>>
>> Incase of recovery, the shared buffers saved by this utility are
>> from previous shutdown which doesn't seem to be of more use
>> than buffers loaded by recovery.
>
> Why? The server might have been queried if it's a hot standby one?

I think that's essentially the same point Amit is making. Gurjeet is
arguing for reloading the buffers from the previous shutdown at end of
recovery; IIUC, Amit, you, and I all think this isn't a good idea.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company