"Juozas Baliuka" <[EMAIL PROTECTED]> writes:
> Think about Gavin's example ( some of my applications use messaging
> too) , most of my applications are integrated with "legacy" systems,
> some of them use "import" it takes ~2 min.

Why couldn't you use optimistic concurrency control for this?
Checkpoint the system, do your import, and if the rows you needed
changed during the 2-minute import, start over.

The "start over" part sounds awful, but the alternative (in a
traditional multiple-outstanding-transaction ACID system) is to leave
those rows locked for two minutes, which is (IMHO) equally awful.

Perhaps I'm missing something here; I've dealt with a lot of
highly-concurrent systems and implemented some hierarchical lock
managers, but I've never dealt with attempted distributed transactions
before.  Could you elaborate on the advantages of pessimistic locking
in this situation?

BTW, I don't really think Prevayler is a complete system, but I think
they have hit upon a good layering that would greatly simplify a lot
of systems.  They've only built the bottommost (very thin) layer; at a
bare minimum you have to add optimistic locking, query parsing, and
query optimization to get anything useful.

  - a

-- 
"Education is not filling a bucket but lighting a fire." -- WB Yeats


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