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From "David Rauschenbach (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-1508) Setting a new property value causes a read of the previous property value
Date Tue, 01 Apr 2008 11:51:51 GMT

    [ https://issues.apache.org/jira/browse/JCR-1508?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12584112#action_12584112
] 

David Rauschenbach commented on JCR-1508:
-----------------------------------------

The only problem with marking this issue as invalid, is that there would be no acknowledgement
that there is a semantic problem in the API. SPI has methods for discovery of metadata, versus
methods for accessing content, and that line is crossed here.

If I want to write a 10k property, it causes a download of a 1GB property value, in order
to discover metadata only. This is a very basic usability problem, caused by a semantic gap
in the API.

This is not a non-issue for people trying to make this API work in the real world, who are
still your best allies, as long as they haven't given up on it yet! :-)

At the heart of this issue is also the RuntimeException that my SPI is forced to throw when
a failure occurs during defererencing the value of a property, which is how I prevent the
download of a previous value over a transport. This RuntimeException is now like those other
RuntimeExceptions in JCR2SPI that we discussed a few months ago, which are all a major problem
in the same category, in my opinion. We are weaving a tangled web, as they say, and it probably
all points to the same semantic gaps in the API, which is causing the impedance mismatch that
would allow all of our methods in the guts of our SPI's or JCR's to simply have RepositoryExceptions
in their method signatures.

> Setting a new property value causes a read of the previous property value
> -------------------------------------------------------------------------
>
>                 Key: JCR-1508
>                 URL: https://issues.apache.org/jira/browse/JCR-1508
>             Project: Jackrabbit
>          Issue Type: Bug
>          Components: jackrabbit-jcr2spi
>    Affects Versions: 1.4
>            Reporter: David Rauschenbach
>
> When using JCR2SPI with a custom SPI, getProperty is called when one attempts to set
a new property value with disregard to the previous value. The current JCR2SPI implementation
causes a getPropertyInfo, which requests the old value from the back-end. This is fundamentally
unsound, and kills performance.
> An SPI has no choice but to guard against this by returning a PropertyInfo proxy that
performs lazy-loading of the value. The problem is that if an error occurs when dereferencing
the value, and when performing the lazy-load, JCR2SPI is ill-suited to hande an unchecked
exception at such a time. Besides, it is a "hack upon a hack", because JCR2SPI could do this
work itself, by making proper use of the SPI functions for requesting property type information.

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