[Dev] Shared transactions

[Brett Wooldridge]

I know it seems like an obvious pattern to use (reference counting) and
slightly simpler than what we have (only slightly), but it has some inherent
flaws which is why JTA (and no transaction manager that I'm aware of)
employs it.  Imagine how easy (code-wise) it would have been for JTA to
embed reference counting in the UserTransaction object.

The first issue is that the transaction may not be initiated by our code.
It could, for example, be initiated inside of Quartz (which has the ability
to run jobs as transactions) or some other third-party library.  Or Bundles
from our codebase could ultimately be run inside of an application server
such has JBoss which itself is managing the transaction boundaries.

A reference counting model could also interfere with Distributed
Transactions which are supported by JTA.  I wouldn't want to close the door
on ZipTie in the future deploying in a multiple-server model and possibly
needing distributed transactions between physical machines (
http://archive.devx.com/java/free/articles/dd_jta/jta-1.asp).

Lastly, two minor nits I would have with a reference counting pattern
(besides those above) is that 1) it would elevate the Elf to being a
Manager, because now it becomes stateful in tracking threads->counters, and
2) I don't like that when debugging and "stepping over" a commit() you don't
really know if that was THE commit or just a dummy commit().  Meaning an
explicit call to commit() from application code is not an explict commit of
the transaction.

-Brett

On 8/27/07 4:01 PM, "Leo Bayer" <lbayer at alterpoint.com> wrote:

> Brett,
>   Instead of doing a beginOrJoin for transactions would it make sense to
> use some sort of "re-entrant" transaction.  Doing so would allow the
> usage of a transaction to not care if it is the owner or not and would
> call commit with the assumption that the last commit in the stack
> performs the actual commit.
> 
> For example:
>   begin(); // begins the transaction
>      begin(); // increments the begin count, does not begin a new
> transaction
>      commit(); // decrements begin count, does not commit
>   commit(); // performs the commit
> 
> Just a thought,
>  - Leo
> 
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