| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz> |
| Cc: | Stephen Frost <sfrost(at)snowman(dot)net>, Adrian Klaver <adrian(dot)klaver(at)gmail(dot)com>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Andres Freund <andres(at)2ndquadrant(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>, 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: | 2014-01-11 21:59:51 |
| Message-ID: | 13657.1389477591@sss.pgh.pa.us |
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Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz> writes [slightly rearranged]
> My 2c is:
> The current behavior in CAP theorem speak is 'Cap' - i.e focused on
> consistency at the expense of availability. A reasonable thing to want.
> The other behavior being asked for is 'cAp' - i.e focused on
> availability. Also a reasonable configuration to want.
> I think an option to control whether we operate 'Cap' or 'cAp'
> (defaulting to the current 'Cap' I guess) is probably the best solution.
The above is all perfectly reasonable. The argument that's not been made
to my satisfaction is that the proposed patch is a good implementation of
'cAp'-optimized behavior. In particular,
> ... Now the desire to
> use sync rather than async is to achieve as much consistency as
> possible, which is also reasonable.
I don't think that the existing sync mode is designed to do that, and
simply lobotomizing it as proposed doesn't get you there. I think we
need a replication mode that's been designed *from the ground up*
with cAp priorities in mind. There may end up being only a few actual
differences in behavior --- but I fear that some of those differences
will be crucial.
regards, tom lane
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