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From "Marcel Reutegger (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-926) Global data store for binaries
Date Wed, 20 Jun 2007 12:56:26 GMT

    [ https://issues.apache.org/jira/browse/JCR-926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12506521
] 

Marcel Reutegger commented on JCR-926:
--------------------------------------

This may be due to caching on the LocalItemStateManager level. If you create a new session
each time you read from the workspace or do random reads on a larger workspace the reading
sessions will be blocked while the binary is written.

I've committed a test case that illustrates the problem:

http://svn.apache.org/repos/asf/jackrabbit/trunk/jackrabbit-core/src/test/java/org/apache/jackrabbit/core/ReadWhileSaveTest.java

Using the default locking strategy in SharedItemState manager the read thread is able to read
127 times on my laptop. When using the fine-grained locking the number goes up to 372.

> 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, DataStore2.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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