hi bryan
On 3/2/07, Bryan Davis <[EMAIL PROTECTED]> wrote:
What persistence manager are you using?
Our tests indicate that the stock persistence managers are a significant
bottleneck for both writes and also initial reads to load the transient
store (on the order of .5 seconds per node when using a remote database like
MSSQL or Oracle).
what do you mean by "load the transient store"?
The stock db persistence managers have all methods marked as "synchronized",
which blocks on the classdef (which means that even different persistence
managers for different workspaces will serialize all load, exists and store
assuming you're talking about DatabasePersistenceManager:
the store/destroy methods are 'synchronized' on the instance, not on
the 'classdef'.
see e.g.
http://java.sun.com/docs/books/tutorial/essential/concurrency/syncmeth.html
the load/exists methods are synchronized on the specific prepared stmt they're
using.
since every workspace uses its own persistence manager instance i can't
follow your conclusion that all load, exists and store operations would be
be globally serialized across all workspaces.
operations). Presumably this is because they allocate a JDBC connection at
startup and use it throughout, and the connection object is not
multithreaded.
what leads you to this assumption?
This problem isn't as noticeable when you are using embedded Derby and
reading/writing to the file system, but when you are doing a network
operation to a database server, the network latency in combination with the
serialization of all database operations results in a significant
performance degradation.
again: serialization of 'all' database operations?
The new bundle persistence manager (which isn't yet in SVN) improves things
dramatically since it inlines properties into the node, so loading or
persisting a node is only one operation (plus the additional connection for
the LOB) instead of one for the node and and one for each property. The
bundle persistence manager also uses prepared statements and keeps a
PM-level cache of nodes (with properties) and also non-existent nodes (which
permits many exists() calls to return without accessing the database).
Changing all db persistence managers to use a datasource and get and release
connections inside of load, exists and store operations and eliminating the
method synchronization is a relatively simple change that further improves
performance for connecting to database servers.
the use of datasources, connection pools and the like have been discussed
in extenso on the list. see e.g.
http://www.mail-archive.com/[email protected]/msg05181.html
http://issues.apache.org/jira/browse/JCR-313
i don't see how getting & releasing connections in every load, exists and store
call would improve preformance. could you please elaborate?
please note that you wouldn't be able to use prepared statements over multiple
load, store etc operations because you'd have to return the connection
at the end
of every call. the performance might therefore be even worse.
further note that write operations must occur within a single jdbc
transaction, i.e.
you can't get a new connection for every store/destroy operation.
wrt synchronization:
concurrency is controlled outside the persistence manager on a higher level.
eliminating the method synchronization would imo therefore have *no* impact
on concurrency/performance.
There is a persistence manager with an ASL license called
"DataSourcePersistenceManager" which seems to the PM of choice for people
using Magnolia (which is backed by Jackrabbit). It also uses prepared
statements and eliminates the current single-connection issues associated
with all of the stock db PMs. It doesn't seem to have been submitted back
to the Jackrabbit project. If you Google for
"com.iorgagroup.jackrabbit.core.state.db.DataSourcePersistenceManager" you
should be able to find it.
thanks for the hint. i am aware of this pm and i had a look at it a couple of
months ago. the major issue was that it didn't implement the correct/required
semantics. it used a new connection for every write operation which
clearly violates the contract that the write operations should occur within
a jdbc transaction bracket. further it creates a prepared stmt on every
load, store etc. which is hardly efficient...
Finally, if you always use the Oracle 10g JDBC drivers, you do not need to
use the Oracle-specific PMs because the 10g drivers support the standard
BLOB API (in addition to the Oracle-specific BLOB API required by the older
9i drivers). This is true even if you are connecting to an older database
server as the limitation was in the driver itself. Frankly you should never
use the 9i drivers as they are pretty buggy and the 10g drivers represent a
complete rewrite. Make sure you use the new driver package because the 10g
driver JAR also includes the older 9i drivers for backward-compatibility.
The new driver is in a new package (can't remember the exact name off the
top of my head).
thanks for the information.
cheers
stefan
Bryan.
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