Re: Proposal : For Auto-Prewarm.

On Thu, Apr 6, 2017 at 4:12 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> On 2017-03-13 18:45:00 +0530, Mithun Cy wrote:
>> I have implemented a similar logic now. The prewarm bgworker will
>> launch a sub-worker per database in the dump file. And, each
>> sub-worker will load its database block info. The sub-workers will be
>> launched only after previous one is finished. All of this will only
>> start if the database has reached a consistent state.
>
> Hm. For replay performance it'd possibly be good to start earlier,
> before reaching consistency. Is there an issue starting earlier?

Thanks Andres for a detailed review. I will try to address them in my next
post. I thought it is important to reply to above comment before that.
Earlier patches used to start loading blocks before reaching a consistent
state. Then Robert while reviewing found a basic flaw in my approach[1].
The function DropRelFileNodesAllBuffers do not expect others to load the
blocks concurrently while it is getting rid of buffered blocks. So has to
delay loading until database reaches consistent state so that we can
connect to each database and take a relation lock before loading any of
theirs blocks.

[1] cannot load blocks without holding relation lock
<https://www.postgresql.org/message-id/CA%2BTgmoYNF_wfdwQ3z3713zKy2j0Z9C32WJdtKjvRWzeY7JOL4g%40mail.gmail.com>

--
Thanks and Regards
Mithun C Y
EnterpriseDB: http://www.enterprisedb.com