On 10/26/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: > This is true of SQLite because isolation in SQLite > is "SERIALIZABLE". This is the highest level of isolate > provided by SQL. Most client/server database engines > by default implement "READ COMMITTED". The value of > "balance" might change between the SELECT and the > UPDATE in MySQL, for example. (I'm less clear about > what happens in PostgreSQL and Oracle. The point ism > that your mileage may vary so be cautious.)
PostgreSQL supports both READ COMMITTED and SERIALIZABLE, but the out-of-box default is READ COMMITTED. It can be selected per-transaction, or changed as a default for all transactions. I believe Oracle is similar. MySQL is a little weird due to different storage engines. From what I can tell, MyISAM doesn't actually support transactions, so you essentially get READ UNCOMMITTED if you try; InnoDB supports all 4 levels and defaults to REPEATABLE READ. The differences between MVCC (Multi-Version Concurrency Control) and locking -based implementations can also show up in corner cases, so it's something you definitely want to look at whenever examing a database engine. ----------------------------------------------------------------------------- To unsubscribe, send email to [EMAIL PROTECTED] -----------------------------------------------------------------------------
