From: | Sailesh Krishnamurthy <sailesh(at)cs(dot)berkeley(dot)edu> |
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To: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Mike Mascari <mascarm(at)mascari(dot)com>, Rod Taylor <rbt(at)rbt(dot)ca>, Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>, PostgreSQL Development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Two weeks to feature freeze |
Date: | 2003-06-23 03:44:39 |
Message-ID: | bxy4r2hsbiw.fsf@datafix.CS.Berkeley.EDU |
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Lists: | pgsql-hackers |
>>>>> "Bruce" == Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
Bruce> Tom Lane wrote:
>> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes: > The question
>> was whether 2PC is useful. The question wasn't if an >
>> unreliable 2PC was useful.
>>
>> My question is whether there is such a thing as reliable 2PC.
>> I sure don't see how you build that.
Bruce> Other databases use 2PC --- are you saying none of them are
Bruce> reliable?
And they use them for both federated read/write (what you refer to as
distributed access through dblink) and for clustered configurations.
I'm not sure if I understand Tom's beef - I think he is concerned
about what happens if a subordinate does not respond to a prepare
message. I would assume that the co-ordinator would not let the commit
go through until it has received confirmations from every
subordinate. The application's commit will remain blocked against the
co-ordinator when this takes place.
That said, I agree that 2PC (and variants) is rather heavy weight when
in widely distributed configurations.
(Although I guess in practice, many people use Presumed Abort and not
vanilla 2PC as PA results in fewer log flushes for read-only
transactions.)
--
Pip-pip
Sailesh
http://www.cs.berkeley.edu/~sailesh
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