RE: [Jdbm-developer] persistent record management -- avoiding con tention.

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

Alex,

That is, you wish to allow updates of the btree from concurrent transactions
to be
"merged" in the sense that the btree ordering after the transactions
reflects the
updates from both?  That feature is certainly important to improving
concurrency
since indices are otherwise likely to become sources of contention between
writers.

-bryan

-----Original Message-----
From: jdb...@li...
[mailto:jdb...@li...] On Behalf Of Alex
Boisvert
Sent: Thursday, February 02, 2006 3:51 PM
To: Kevin Day
Cc: JDBM Developer listserv
Subject: Re: [Jdbm-developer] persistent record management -- avoiding
contention.



I think different transaction must get different copies of objects otherwise
it would place an undue burden on application developers.

Data structures (e.g. BTree) are a different kind of beast because we need
to ensure that commutative operations are allowed between
transactions.   Therefore, they must participate more closely with the
transaction's concurrency control mechanism to achieve concurrent updates
whenever possible.

alex

Kevin Day wrote:

> Finally, I really think that we need to all (Alex - time for you to 
> join in the discussion!) have at minimum an initial discussion of the 
> implications of simultaneous transactions to ACID behavior...  There 
> are some very big issues here that I think we need to think through 
> before we do much anything...  The biggest of these issues, as I see 
> it, is whether different transacations get their own copies of objects 
> or not - if they get their own copy, then it precludes the use of 
> higher level syncrhonization for managing complicated data structures 
> (e.g. it would be impossible to synchronize on a BTree to ensure that 
> the data structure remains valid during re-balancing, etc...).  If 
> transactions share a copy of the same instance of a given object, then 
> Isolation is pretty much trashed.




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