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From "Thomas Mueller (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-926) Global data store for binaries
Date Fri, 31 Aug 2007 07:34:30 GMT

    [ https://issues.apache.org/jira/browse/JCR-926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12524022
] 

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

Hi,

Theoretically the data store could be split to different directories / hard drives. Content
that is accessed more often could be moved to a faster disk, and less used data could eventually
be moved to slower / cheaper disk. That would be an extension of the 'memory hierarchy' (see
also http://en.wikipedia.org/wiki/Memory_hierarchy). Of course this wouldn't limit the space
used per workspace, but would improve system performance if done right. Maybe we need to do
that anyway in the near future to better support solid state disk. 

Workspace usage: I'm not sure what solution would be the best for your use case. Maybe this
would better be discussed in a separate thread. See also http://wiki.apache.org/jackrabbit/DavidsModel#head-ca639e0ee110b80e8277a50f9b9de092b5d86427

> 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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