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