Note in-line
--
Regards
Jonathan Lewis
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<ctcgag_at_hotmail.com> wrote in message
news:20040620152317.432$RM_at_newsreader.com...
>
> > I think that's what most people would expect of serializable.
>
> Not I. I would expect one of the two to get a "cannot serialize" error.
> The isolation level that Oracle calls "serializable" is not truly
> serializable. I'm not saying that that level isn't useful, nor am I
saying
> that it could be made truly serializable without incurring significant
> performance penalties. I'm just saying they probably shouldn't have named
> it "serializable" when it really isn't.
>
I sympathise with the view-point. Life gets difficult when
words are given a specific meaning for a technical context
that doesn't match the 'intuitive' meaning outside that context.
At the time, of course, 'serializable' was described twice in
the SQL standard: and one of the descriptions was a list of
the phenomena that qualify a serializable transactions -
one of which was "repeatable reads". So Oracle put three
ticks against the list, and said "that's it - we comply to that
feature".
I must read the latest standard some time to see what it
says on the topic.
Your comment leads to an interesting philosophical point -
I execute a serializable transaction, but do NOT
revisit row X, which gets changed and committed
by another user in the interim.
I execute the same serializable transaction, but DO
revisit row X, which gets changed and committed
by another user in the interim. However, there is
nothing in my transaction that I do differently, whether
or not I can see the change (which I couldn't in Oracle
of course).
Should either, neither, or both of those transaction fail
according to your concept of serializable ?
I think this may qualify as the "Schrödinger's Cat" of the
serializable transaction.
(Side-note: my spell-checker wants to change the American
spelling of serializable into "fertilizable" - does this mean the
entire discussion is a load of horse-manure ?)
Received on Wed Jun 23 2004 - 04:06:53 CDT
