Subject Re[2]: [Firebird-Architect] Supported transaction isolation levels?
Author Dmitry Kuzmenko
Hello, Thomas!

Tuesday, April 5, 2005, 11:17:14 PM, you wrote:

TS> The weird thing now is that the MySQL folks claim that the InnoDB table
TS> type supports ACID-compliant transactions with all four isolation levels
TS> and even support of the MVCC model. Well, this is off-topic here, but I
TS> do find it somewhat strange.

maybe. Firebird architects up to now struggles against Dirty Read,
while it can be implemented in MGA extending read_committed
no_rec_version isolation mode. But, implementing Repeatable Read
exactly as in standard could be tricky, since it allows fanthom reads.

I.e. itself versioning engine can easlily support Dirty Read,
Read Committed and Snapshot isolation levels (Snapshot is stronger
than Repeatable Read). But, Serializable isolation needs something
like "serial transation pool" which I think doesn't have anything
related to MGA or any other locking scheme.

You may know, that new MS SQL version (Yukon) will also use
versioning, behaving like IB/FB versioning. But, some people
have suspects about its functioning, because of internal
MVCC implementation in Yukon (there was a big article about
versioning in Yukon in one russian magazine, I'm not sure
this article was translated into english).

Dmitri Kouzmenko,