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Re: incoherent view of serializable transactions

From: Peter Eisentraut <peter_e(at)gmx(dot)net>
To: Greg Stark <greg(dot)stark(at)enterprisedb(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Subject: Re: incoherent view of serializable transactions
Date: 2008-12-30 08:56:43
Message-ID: 4959E24B.9040900@gmx.net (view raw or flat)
Thread:
Lists: pgsql-hackers
Greg Stark wrote:
> And I don't see why you discard "visibility" as unimportant. All the 
> transaction isolations are defined in terms of the results if the 
> transactions. Those results include both the database state and the data 
> returned by the queries. Otherwise "phantom read" is a meaningless concept.

Basically, if he wants to make a rigid argument that some scenario 
violates the serializability promise, then it is necessary to prove:

(1) There is no serial schedule for the set of transactions that 
achieves the same outcome.  (This proof is probably hard to work out, as 
many "there is no" proofs are.)

- or -

(2) A phantom read situation occurs.

His original argument uses terms like "window" where something is 
"visible" (to whom?), which can probably be transformed into a proof for 
(2), but is not convincing (to me) by itself.


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