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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 Wed, 13 Jun 2007 17:30:26 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12504343
] 

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

Thanks for the additional modifications, Narayanan.

>>5) Why is incrementUpdateCount() called in these streams? Shouldn't the update count
be
>> incremented by the Blob and Clob methods which do the actual writing?
>
>   readCharacters, writeCharacters, writeBytes on the Locator streams forward their calls
to
>   the framework that calls the stored procedures with the locator value obtained
>   from the Lob. The only way to reach the update count being the Lob reference
>   >\that is maintained within these streams.
>
> ...

I think I'm missing something. BlobLocatorOutputStream.writeBytes() does the following:

            connection.locatorProcedureCall()
                .blobSetBytes(blob.locator_, currentPos, b.length, b);

            ...

            blob.incrementUpdateCount();

Why can't BlobLocatorOutputStream.writeBytes()  do something like the following, instead:

            blob.setBytesX( currentPos, b, 0, b.length );

Blob.setBytesX() already increments the update count and there is no need for BlobLocatorOutputStream
to do this. I think that the bumping of the update count should be encapsulated in the Lob
and incrementUpdateCount() should be a private method.

> 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, UpdateSensitiveStreamsForClient_v2.diff, UpdateSensitiveStreamsForClient_v2.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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