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https://issues.apache.org/jira/browse/DERBY-2496?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Øystein Grøvlen updated DERBY-2496:
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Attachment: blob.diff
The attached patch, blob.diff, adds support for locators for Blob methods and
ResultSet.getXXX methods. Note that the use of locators for Blob is still not
enabled. The other steps mentioned in this Jira is also needed before locators
can be used.
Another thing to note about this patch is that the implementation of locator
based streams are pretty basic. No bufferering is done. Hence, the byte[]
versions of read/write should be used if performance is a concern. (The
parameterless versions of read/write will only send one byte per client/server
round-trip.)
More detailed description of changes:
M java/client/org/apache/derby/client/net/NetStatementRequest.java
* Do not request locators for Clob, only Blob. Necessary to be able to add
locators for Blob independently of Clob.
M java/client/org/apache/derby/client/net/NetCursor.java
* If locator is sent, do not assume any external data. (If external data
highest bit of in-place column value will be set.)
* Create locator based Blob object if locator is sent.
M java/client/org/apache/derby/client/am/Cursor.java
* Made get_INTEGER protected so sub-classes (Netcursor) can use it to read
locator value.
M java/client/org/apache/derby/client/am/Blob.java
* Add constructor for locator based Blob object.
* Make all Blob operations support locators. Operations are performed by
calling stored procedures through the framework implemented by
CallableLocatorProcedures class.
* Create locator based versions of streams for locator based Blob objects
M java/client/org/apache/derby/client/am/Lob.java
* Added locator field to record locator of locator based Lobs and a new
constant to be used to record the data type to be Locator based.
* If locator based and length not yet obtained, sqlLength() will call
getLocatorLength() to get the length.
* A dummy implementation of getLocatorLength() is added, subclasses should
override.
* Add methods for checking if Lob is locator based, and for returning the
locator value.
A java/client/org/apache/derby/client/am/BlobLocatorOutputStream.java
* OutputStream for locator based Blob.
* No buffering is done. Hence, for efficiency, byte[] version of write
should be used.
A java/client/org/apache/derby/client/am/BlobLocatorInputStream.java
* InputStream for locator based Blob.
* No buffering is done. Hence, for efficiency, byte[] version of read
should be used.
> Implement Blob support for Locators
> -----------------------------------
>
> Key: DERBY-2496
> URL: https://issues.apache.org/jira/browse/DERBY-2496
> Project: Derby
> Issue Type: Sub-task
> Reporter: Øystein Grøvlen
> Assigned To: Øystein Grøvlen
> Attachments: blob.diff
>
>
> DERBY-2347 adds the possibility to send locators between client and server
> instead of LOB values. This has not been activated yet, since the client
> implementation does not currently support locators. This report is for
> supporting the locators for Blob objects. Another JIRA issue will be made
> for Clob.
> This work will be made in several steps:
> 1. Blob methods and ResultSet.getXXX methods
> 2. PreparedStatement and CallableStatement methods
> 3. ResultSet.updateXXX methods
> 4. Connection.createBlob()
> There is dependencies between these steps and it might be that the Locator
> implementation cannot be exposed until everything has been done. At least,
> doing just step 1, gives testing errors because tests use Blobs fetched from
> DB as parameters to prepared statements. I would guess tests for updatable
> result sets, needs the combination of 1. and 3.
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