Re: How does concurrency control work in WO?
Re: How does concurrency control work in WO?
- Subject: Re: How does concurrency control work in WO?
- From: Andrew Lindesay <email@hidden>
- Date: Mon, 30 Mar 2009 11:51:33 +1300
Hello Kevin;
Also try to understand what's diff between multi-EOF and DB
connection pool in J2EE, (like weblogic, tomcat or webshpere).
Further how is J2EE world solve this concurrency issue?
Using a number of object-store-coordinators (OSCs) will create
snapshot-storage for each. This means that you may need more memory
because for commonly accessed EO's, their snapshots will have to
reside in each of the OSC's snapshot storage. This is perhaps memory-
inefficient, but may or may not actually be a problem for a specific
project. The usual means of gaining concurrent throughput through a
WOA deployment is of course, to deploy a number of instances. Each
instance then gets it's own default OSC and because you have different
virtual machines, the memory required to support this can be
distributed over additional hosts. As has been eluded to by other
people, a common problem is that each OSC's snapshots can then get out
of sync with each other and the realities of the database. To solve
this, people either fetch some data often or use a "change
notification" system to spread the changes around the deployment and
try to keep all the OSC's and the database in sync.
I am not familiar with how other java object-relational systems like
TopLink, Hibernate and Cayenne (Andrus - can you elaborate?) deal with
"connection pooling" and persistence-layer concurrency in J2EE, but if
you are doing raw SQL (gasp) and abandoning everything that a
relational-modeller can do for you then at a low level, different
threads are able to grab a SQL connection, use it and then return it
to the pool for another thread to use. In this way, a number of
threads are able to access the database at the same time.
Problems, if there are any at all, will most likely be very different
for different sorts of projects. In using a change-notification
system, I've only actually had a couple of cases where other concrete
issues in this area have arisen for me.
cheers.
___
Andrew Lindesay
www.lindesay.co.nz
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