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Re: Re: new patch of MERGE (merge_204) & a question about duplicated ctid

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Florian Pflug <fgp(at)phlo(dot)org>
Cc: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Greg Smith <greg(at)2ndquadrant(dot)com>, Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>, Boxuan Zhai <bxzhai2010(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: new patch of MERGE (merge_204) & a question about duplicated ctid
Date: 2011-01-03 17:09:32
Message-ID: AANLkTikUAYDhRkLv3MVRYUFuXua69_m944-kXwav8QAJ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Jan 3, 2011 at 11:36 AM, Florian Pflug <fgp(at)phlo(dot)org> wrote:
> On Jan3, 2011, at 17:21 , Robert Haas wrote:
>> On Mon, Jan 3, 2011 at 11:08 AM, Heikki Linnakangas
>>> In serializable mode you get a serialization error.
>>
>> I don't think this part is true.  You can certainly do this:
>>
>> CREATE TABLE test (a int);
>> BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
>> SELECT * FROM test;
>> <in another session, insert (1) into test>
>> LOCK TABLE test IN SHARE MODE; -- or just LOCK TABLE test, if you prefer
>> SELECT * FROM test;  -- still ain't there
>> INSERT INTO test VALUES (1);
>
> In SERIALIZABLE mode, you need to take any table-level locks before obtaining
> a snapshot. There's even a warning about this in the docs somewhere IIRC...

That should be safe, if people do it that way.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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