Jackrabbit has its own multi threaded state management. Everything is
focused on serving information from memory and not performing a query
against the database. Only when a session needs to get something that
isn't in one of the shared caches will you see queries hitting the
database.
On the persistent manager connection you will probably see a stream of
insert and update statements (perhaps with some selects), but you will
not see the same volume of selects that you saw with a normal RDBMS
application since most activity will be services from shared cache.
The one connection where you will see activity is the Journal
connection that last time I looked in 1.4 needs to serialize the
journal creation so that all nodes can perform replays in step. Hence
there will be a select to generate a new sequence, and an insert to
save the sequence.
The side effect of all of this is that jackrabbit can support a higher
level of concurrency in the web application layer than you would be
able to support if each request thread required a database connection.
The JCR sessions are lighter weight than JDBC sessions simply because
they don't require a network connection. (although pooling removes
that need)
However, if you are seeing excessive SQL traffic, and would like to
reduce it, using an XATransaction manager (eg from JTA) will batch up
the SQL traffic to when the transaction is committed and the transient
state is persisted from the session state.
To make jackrabbit use one connection per thread, you would have to
refactor quite a lot of code above the persistence manager. I suspect
writing a new Jackrabbit SPI implementation would do this, but thats
certainly not trivial.
HTH
Ian
On 28 Apr 2009, at 14:47, majohnst wrote:
I am trying to better understand how Jackrabbit performs queries on
a mysql
database filestore/persistance manager. I understand that when
Jackrabbit
starts, it creates several persistent connections to the database.
One for
the datastore, one for the workspace, one for the journal (for
clustering),
etc. Jackrabbit cannot use connection pools, so there is no need to
setup a
database connection pool.
My question is, when I query jackrabbit (or other jcr operation that
needs
to read from the mysql database), is there really only one
connection to my
mysql database? Do all queries go into a queue and only one query is
executed at a time? So there is no idea of simultaneous querying with
jackrabbit? Is there any way to increase the number of queries
jackrabbit
can do at one time?
Our application has a very high number of concurrent users and we
are seeing
a slow down because jackrabbit cannot execute the queries fast
enough. I am
hoping that there is a way I can increase the number of queries that
jackrabbit can execute at one time.
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