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https://issues.apache.org/jira/browse/JCR-314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12525131
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Pablo Rios commented on JCR-314:
--------------------------------
It seems that when XA transactions are used the fine grained ISM locking
strategy *always* block readers when there is a writer, because the root node
of the version histories always has a dependency on the active writer changelog.
>From XAVersionManager constructor
try {
state = (NodeState) stateMgr.getItemState(vMgr.getHistoryRootId());
} catch (ItemStateException e) {
...
}
Am I wrong or right ?
> 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, writes-per-second.jpg
>
>
> 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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