From: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
---|---|
To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Andres Freund <andres(at)2ndquadrant(dot)com> |
Subject: | Re: Spreading full-page writes |
Date: | 2014-05-27 07:49:00 |
Message-ID: | CAHGQGwEeep45nBRSBq_DpZC4J++nB8dpj2vQJik_HyLENhsrRQ@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Tue, May 27, 2014 at 3:57 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On 25 May 2014 17:52, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> wrote:
>
>> Here's an idea I tried to explain to Andres and Simon at the pub last night,
>> on how to reduce the spikes in the amount of WAL written at beginning of a
>> checkpoint that full-page writes cause. I'm just writing this down for the
>> sake of the archives; I'm not planning to work on this myself.
> ...
>
> Thanks for that idea, and dinner. It looks useful.
>
> I'll call this idea "Background FPWs"
>
>> Now, I'm sure there are issues with this scheme I haven't thought about, but
>> I wanted to get this written down. Note this does not reduce the overall WAL
>> volume - on the contrary - but it ought to reduce the spike.
>
> The requirements we were discussing were around
>
> A) reducing WAL volume
> B) reducing foreground overhead of writing FPWs - which spikes badly
> after checkpoint and the overhead is paid by the user processes
> themselves
> C) need for FPWs during base backup
>
> So that gives us a few approaches
>
> * Compressing FPWs gives A
> * Background FPWs gives us B
> which look like we can combine both ideas
>
> * Double-buffering would give us A and B, but not C
> and would be incompatible with other two ideas
Double-buffering would allow us to disable FPW safely but which would make
a recovery slow. So if we adopt double-buffering, I think that we would also
need to overhaul the recovery.
Regards,
--
Fujii Masao
From | Date | Subject | |
---|---|---|---|
Next Message | Heikki Linnakangas | 2014-05-27 08:49:07 | Re: Spreading full-page writes |
Previous Message | Matteo Beccati | 2014-05-27 07:34:14 | Re: [PATCH] Replacement for OSSP-UUID for Linux and BSD |