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Re: Synchronous replication, reading WAL for sending

From: "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com>
To: "Fujii Masao" <masao(dot)fujii(at)gmail(dot)com>
Cc: "Heikki Linnakangas" <heikki(dot)linnakangas(at)enterprisedb(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "Pavan Deolasee" <pavan(dot)deolasee(at)enterprisedb(dot)com>
Subject: Re: Synchronous replication, reading WAL for sending
Date: 2008-12-24 08:48:55
Message-ID: 2e78013d0812240048x440e907aw190ecee0f47a9224@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, Dec 24, 2008 at 1:50 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>
>
> And, I'm worried about the situation that the speed to generate xlog
> on the primary is higher than that to copy them to the standby. We
> might not be able to start xlog streaming forever.
>

If that's the case, how do you expect the standby to keep pace with
the primary after initial sync up ? Frankly, I myself have every doubt
that on a relatively high load setup, the standby will not be able
keep pace with the primary for two reasons:

- Lack of read ahead of data blocks (Suzuki-san's work may help this)
- Single threaded recovery

But then these are general problems which may impact any log-based replication.

Thanks,
Pavan

-- 
Pavan Deolasee
EnterpriseDB     http://www.enterprisedb.com

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