From: | Florian Pflug <fgp(at)phlo(dot)org> |
---|---|
To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
Cc: | Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Differential backup |
Date: | 2010-04-27 14:22:08 |
Message-ID: | 541B54F7-94AB-42A4-AB41-F3B2BB05F582@phlo.org |
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Lists: | pgsql-hackers |
On Apr 27, 2010, at 16:08 , Simon Riggs wrote:
> On Tue, 2010-04-27 at 08:59 -0500, Kevin Grittner wrote:
>> Why? I must be missing something, because my feeling is that if you
>> can't trust your OS to cover something like this, how can you trust
>> any application *running* under that OS to do it?
>
> Good questions. I'm exploring a perceived need.
>
> I don't think people want this because they think the OS is flaky. It's
> more about trusting all of the configurations of all of the filesystems
> in use. An explicit mechanism would be more verifiably accurate. It
> might just be about control and blame.
I believe a reason for people (including me) to not have 100% faith in file modification times are non-monotone system clocks. I've seen more than one system where a cron job running ntpdate every night was used as a poor man's replacement for ntpd...
So the real advantage of rolling our own solution is the ability to use LSNs instead of timestamps I'd say.
best regards,
Florian Pflug
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