User: Password:
|
|
Subscribe / Log in / New account

The birth of the open source enterprise stack

The birth of the open source enterprise stack

Posted Jul 7, 2006 0:38 UTC (Fri) by nix (subscriber, #2304)
In reply to: The birth of the open source enterprise stack by pimlott
Parent article: The birth of the open source enterprise stack

The PostgreSQL manual makes the point that perfect isolation isn't possible without giving the database what amounts to a theorem prover *and* complete knowledge of your app's control flow
I'm curious what you're talking about, because I can't find anything like that in the PostgreSQL manual. I think perfect isolation is straightforward using read and write logs, and that PostgreSQL does exactly that. What am I missing?
See section 12.2.2.1 of the PostgreSQL manual, and the discussion of predicate locking. (Note, when it says `the details of every query', it means the details. In the presence of random-access cursors I suspect this reduces to solving the halting problem.)
But what do you mean about transactions going read-only?
If you turn on serializable isolation in some transaction in said expensive proprietary RDBMS, you can no longer carry out INSERTs or UPDATEs in that transaction. It makes it really very useful :/


(Log in to post comments)

The birth of the open source enterprise stack

Posted Jul 7, 2006 1:24 UTC (Fri) by pimlott (guest, #1535) [Link]

See section 12.2.2.1 of the PostgreSQL manual, and the discussion of predicate locking.
Thank you, I am enlightened. I guess this could be solved by logging at the table level: when the where clause is non-trivial, mark the entire table read, and mark the table written on insert. Then, when you commit, you would see (in one of the transactions) that the table has been modified since you queried it.
If you turn on serializable isolation in some transaction in said expensive proprietary RDBMS, you can no longer carry out INSERTs or UPDATEs in that transaction.
Hmm... I've used serializable in (if memory serves) Informix, Oracle, and Sybase, reading and writing. Have I not gone expensive enough?

The birth of the open source enterprise stack

Posted Jul 8, 2006 22:58 UTC (Sat) by nix (subscriber, #2304) [Link]

My experience of Oracle is that at least in some releases, it had (and was documented as having!) the nasty read-only semantics I described :(


Copyright © 2017, Eklektix, Inc.
Comments and public postings are copyrighted by their creators.
Linux is a registered trademark of Linus Torvalds