[jira] Commented: (JCR-314) Fine grained locking in SharedItemStateManager

["Pablo Rios (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/JCR-314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12525131 ] 

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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