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From "Marcel Reutegger (JIRA)" <j...@apache.org>
Subject [jira] Updated: (JCR-314) Fine grained locking in SharedItemStateManager
Date Wed, 23 May 2007 11:02:17 GMT

     [ https://issues.apache.org/jira/browse/JCR-314?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Marcel Reutegger updated JCR-314:
---------------------------------

    Attachment: FineGrainedISMLocking-v2.patch

Here's a new version of FineGrainedISMLocking.

The performance should be better compared to the last version.

I'm not sure the test case is very representative though. Lot of monitor contention happens
between the write thread and readers when item states are notified and the cache maps need
to be accessed. I think finer grained locking makes this situation even worse because it allows
more concurrency on the caches.

> Fine grained locking in SharedItemStateManager
> ----------------------------------------------
>
>                 Key: JCR-314
>                 URL: https://issues.apache.org/jira/browse/JCR-314
>             Project: Jackrabbit
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 0.9, 1.0, 1.0.1, 1.1, 1.1.1, 1.2.1, 1.2.2, 1.2.3
>            Reporter: Marcel Reutegger
>         Attachments: FineGrainedISMLocking-v2.patch, FineGrainedISMLocking.patch, ISMLocking.patch
>
>
> The SharedItemStateManager (SISM) currently uses a simple read-write lock to ensure data
consistency. Store operations to the PersistenceManager (PM) are effectively serialized.
> We should think about more sophisticated locking to allow concurrent writes on the PM.
> One possible approach:
> If a transaction is currently storing data in a PM a second transaction may check if
the set of changes does not intersect with the first transaction. If that is the case it can
safely store its data in the PM.
> This fine grained locking must also be respected when reading from the SISM. A read request
for an item that is currently being stored must be blocked until the store is finished.

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