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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2763) In the Network Client InputStreams and Readers returned from LOB's should be sensitive to underlying LOB data changes.
Date Tue, 12 Jun 2007 17:34:26 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12503939
] 

Rick Hillegas commented on DERBY-2763:
--------------------------------------

Thanks for the quick response, Narayanan. I think I can see how this patch reduces the possibility
of the inconsistency which you describe. However, I think that there are race conditions in
this patch which could still give rise to that inconsistency--because the read() methods handshake
with the writers on entry and not on exit.

Inconsistencies of some sort can always arise if the contents of the LOB change between the
time that reading starts and the time that reading ends. I think that's true with or without
this patch. This patch may change the kind of inconsistencies that can occur and this patch
may reduce the possibility of certain inconsistencies. Whether those inconsistencies are acceptable
depends on what the application is doing and what it expects.

What I'm struggling to understand is this: why are the inconsistencies allowed by this patch
better than the inconsistencies allowed if we don't do anything? What are the supported use-cases
which we want to document? If I understood those use-cases, then I could reason about whether
this patch actually delivers the intended benefit.

Thanks!

> In the Network Client InputStreams and Readers returned from LOB's should be sensitive
to underlying LOB data changes.
> ----------------------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-2763
>                 URL: https://issues.apache.org/jira/browse/DERBY-2763
>             Project: Derby
>          Issue Type: Bug
>          Components: Network Client
>    Affects Versions: 10.3.0.0
>            Reporter: V.Narayanan
>            Assignee: V.Narayanan
>             Fix For: 10.3.0.0
>
>         Attachments: Approach_2.diff, Approach_2.stat, Approach_2.txt, Approach_3.diff,
Approach_3.stat, Approach_4.diff, Approach_4.stat, LOBLengthPersists.java, UpdateSensitiveStreamsForClient_v1.diff,
UpdateSensitiveStreamsForClient_v1.stat
>
>
> Currently the Embedded and Network Client would differ 
> in behaviour when the following series of steps is 
> followed.
> a) Create an empty Blob
> b) get an InputStream using Blob.getBinaryStream()
> c) write data into this Blob
>    c.1) Get an OutputStream
>    c.2) Use OutputStream.write(byte [] b) to write
>         into this Blob.
> d) Now read from the InputStream obtained in step b)
>    and print the number of bytes read as output.
> The output of step d) differs in the client and in the Embedded side.
> In the Client
> -------------
> The number of bytes read would always be -1.
> In the Embedded
> ---------------
> The number of bytes would be the number of bytes we
> reflected.
> The above behaviour in the NetworkClient is because
> the length of the Blob is read once and stored in the 
> constructor of the locator Stream returned (in the 
> attribute maxPos).
> This instead should be read each time we use the streams.
> A similar issue exists for Clobs also.
> I will raise a seperate JIRA issue for this.

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