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Re: Re: [COMMITTERS] pgsql: Make CheckRequiredParameterValues() depend upon correct

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: [COMMITTERS] pgsql: Make CheckRequiredParameterValues() depend upon correct
Date: 2010-04-29 18:24:17
Message-ID: 1272565457.4161.14227.camel@ebony (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
On Thu, 2010-04-29 at 13:01 -0500, Kevin Grittner wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> wrote:
>  
> > I've asked for evidence that recovery is any slower as a result of
> > HS.
>  
> Can you quantify the impact on the number of bytes written to WAL
> when switching from the archiving level to the hot standby level?

Sure, done that a few times.

Extra WAL data is written for these actions, listed in order of
increasing size

* commit records contain a variable length list of
relcacheinvalidations, mostly applies only to DDL
* one extra WAL record in most VACUUMs, fairly small, optimised away in
some cases
* a transaction issues more than 64 subtransactions it will issue a
record approx 256 bytes plus header
* one extra WAL record every checkpoint, containing a full current
snapshot's worth of running xids 100-400 bytes typically, could go up
from there to 4000 bytes in very extreme write workloads that also have
many, many subtransactions

-- 
 Simon Riggs           www.2ndQuadrant.com


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