RE: re[12]: [Jdbm-developer] re[2]: DefaultTransactionManager - d r aft of prototype.

[Thompson, B. B. <BRY...@sa...>]

Sure.  I think that SF CVS is still out, but they are predicting an online
status by wed.

 

http://sourceforge.net/docman/display_doc.php?docid=2352
<http://sourceforge.net/docman/display_doc.php?docid=2352&group_id=1>
&group_id=1

 

-bryan

 

  _____  

From: jdb...@li...
[mailto:jdb...@li...] On Behalf Of Kevin Day
Sent: Tuesday, April 04, 2006 1:12 PM
To: JDBM Developer listserv
Subject: re[12]: [Jdbm-developer] re[2]: DefaultTransactionManager - d r aft
of prototype.

 

Bryan-

 

Bingo!  That is why I have been so excited about MVCC.  It makes it so the
locking is used only for what it needs to be used for, and gives more
control over the overall concurrency issue.

 

The really slick thing about this is that it seriously helps optimistic
concurrency, because there is only one type of isolation level that can be
violated under MVCC :  Serializable.  Many, many applications don't even
need that level of isolation, and those that do can often work with simple
synchronization constructs to prevent the issue from even arising.

 

I've got to figure out how to get this code into your hands - maybe I'll
send it in zip file this evening.

 

- K

 

  


 

> 
So, locking imposes an ordering constraint on the execution of transactions
but the data view is governed by MVCC? 
 


From: jdb...@li...
<mailto:jdb...@li...>
[mailto:jdb...@li...]
<mailto:jdb...@li...>  On Behalf Of Kevin Day
Sent: Tuesday, April 04, 2006 1:00 PM
To: JDBM Developer listserv
Subject: re[10]: [Jdbm-developer] re[2]: DefaultTransactionManager - dr aft
of prototype. 
 

Bryan- 

 

Locking provides transaction serialization isolation only.  Read
Uncommitted, Read Committed and Repeatable Read are entirely provided by the
MVCC layer. 

 

- K 

  

 
> 
Expand on this please.  What is the role fulfilled by locking in this
design? -bryan 
 


From: jdb...@li...
<mailto:jdb...@li...>
[mailto:jdb...@li...]
<mailto:jdb...@li...>  On Behalf Of Kevin Day
Sent: Tuesday, April 04, 2006 10:40 AM
To: JDBM Developer listserv
Subject: re[8]: [Jdbm-developer] re[2]: DefaultTransactionManager - dr aft
of prototype. 
 

Bryan- 

 

This is completely different with MVCC.  Transactions operate in complete
isolation from each other, regardless of what type of locking you use. 

 

In the proof of concept I've put together, you can release locks whenever
you want without violating isolation.  Locking is only necessary to ensure
serializability. 

 

Nice, eh? 

 

- K 

  
<SNIP>
 
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