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From "Thomas Mueller (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-926) Global data store for binaries
Date Wed, 12 Sep 2007 09:29:32 GMT

    [ https://issues.apache.org/jira/browse/JCR-926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12526722
] 

Thomas Mueller commented on JCR-926:
------------------------------------

Compatibility: the plan is to make this feature fully backward compatible. When the system
property 'org.jackrabbit.useDataStore' is enabled, and when FileDataStore is configured in
repository.xml, old repositories can still be used. Only new binary objects are stored in
the data store, and only when this is configured in repository.xml.

Migration to data store: binary data that is currently in the blob store (or in the persistence
manager) can be moved to the data store by cloning a workspace, or export / import.

Migration away from the data store: currently, you need to export the data with the data store
enabled / configured, and then import into a new repository without data store.

> Global data store for binaries
> ------------------------------
>
>                 Key: JCR-926
>                 URL: https://issues.apache.org/jira/browse/JCR-926
>             Project: Jackrabbit
>          Issue Type: New Feature
>          Components: core
>            Reporter: Jukka Zitting
>         Attachments: dataStore.patch, DataStore.patch, DataStore2.patch, dataStore3.patch,
dataStore4.zip, dataStore5-garbageCollector.patch, internalValue.patch, ReadWhileSaveTest.patch
>
>
> There are three main problems with the way Jackrabbit currently handles large binary
values:
> 1) Persisting a large binary value blocks access to the persistence layer for extended
amounts of time (see JCR-314)
> 2) At least two copies of binary streams are made when saving them through the JCR API:
one in the transient space, and one when persisting the value
> 3) Versioining and copy operations on nodes or subtrees that contain large binary values
can quickly end up consuming excessive amounts of storage space.
> To solve these issues (and to get other nice benefits), I propose that we implement a
global "data store" concept in the repository. A data store is an append-only set of binary
values that uses short identifiers to identify and access the stored binary values. The data
store would trivially fit the requirements of transient space and transaction handling due
to the append-only nature. An explicit mark-and-sweep garbage collection process could be
added to avoid concerns about storing garbage values.
> See the recent NGP value record discussion, especially [1], for more background on this
idea.
> [1] http://mail-archives.apache.org/mod_mbox/jackrabbit-dev/200705.mbox/%3c510143ac0705120919k37d48dc1jc7474b23c9f02cbd@mail.gmail.com%3e

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