| From: | Stephen Frost <sfrost(at)snowman(dot)net> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Hannu Krosing <hannu(at)2ndquadrant(dot)com>, MauMau <maumau307(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kevin Grittner <kgrittn(at)ymail(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Rajeev rastogi <rajeev(dot)rastogi(at)huawei(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Standalone synchronous master |
| Date: | 2014-01-10 22:02:08 |
| Message-ID: | 20140110220208.GX2686@tamriel.snowman.net |
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| Lists: | pgsql-hackers |
* Andres Freund (andres(at)2ndquadrant(dot)com) wrote:
> On 2014-01-10 10:59:23 -0800, Joshua D. Drake wrote:
> > If a synchronous slave goes down, the master continues to operate. That is
> > all. I don't care if it is configurable (I would be fine with that). I don't
> > care if it is not automatic (e.g; slave goes down and we have to tell the
> > master to continue).
>
> Would you please explain, as precise as possible, what the advantages of
> using a synchronous standby would be in such a scenario?
In a degraded/failure state, things continue to *work*. In a
non-degraded/failure state, you're able to handle a system failure and
know that you didn't lose any transactions.
Tom's point is correct, that you will fail on the "have two copies of
everything" in this mode, but that could certainly be acceptable in the
case where there is a system failure. As pointed out by someone
previously, that's how RAID-1 works (which I imagine quite a few of us
use).
I've been thinking about this a fair bit and I've come to like the RAID1
analogy. Stinks that we can't keep things going (automatically) if
either side fails, but perhaps we will one day...
Thanks,
Stephen
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