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Re: Documenting serializable vs snapshot isolation levels

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: "Robert Haas" <robertmhaas(at)gmail(dot)com>, "Simon Riggs" <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Documenting serializable vs snapshot isolation levels
Date: 2009-01-02 18:47:51
Message-ID: 26455.1230922071@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
>> What do you mean by referential integrity?  I don't believe you can
>> construct a foreign key problem at any transaction isolation level.
 
> I mean that if someone attempts to maintain referential integrity with
> SQL code, without using explicit locks, it is not reliable. 
> Presumably the implementation of foreign keys in PostgreSQL takes this
> into account and blocks the kind of behavior shown below.  This
> behavior would not occur with true serializable transactions.

IIRC the RI code has to fudge the normal serializable-snapshot behavior
in order to guarantee no constraint violation --- it has to be aware of
concurrent changes that would otherwise be invisible to a serializable
transaction.

			regards, tom lane

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