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From "Tomohito Nakayama (JIRA)" <derby-...@db.apache.org>
Subject [jira] Updated: (DERBY-326) Improve streaming of large objects for network server and client
Date Thu, 29 Dec 2005 14:14:03 GMT
     [ http://issues.apache.org/jira/browse/DERBY-326?page=all ]

Tomohito Nakayama updated DERBY-326:

    Attachment: DERBY-326.patch

Description of patch :
   * Remove processing to expand data from InputStream of blob/clob to memory before sending
to client.
    * Implement layer B streaming at NetworkServer.
     * As written in this issue firstly, almost rewrite whole org.apache.derby.impl.drda.DDMWriter#writeScalarStream.
       Here , "almost" means that code was not wrote from scratch, but was wrote as reform.
       Remarkable point is as next :
       Original code was using variable "bytesToRead" to handle remaining amount of data sent
and remaining roon in DSS segment .
       Now this variable "bytesToRead" was removed from.
       New code, instead, have variable "spareDssLength" to handle remaining room in DSS segment
    * Modify org.apache.derby.impl.drda.EXTDTAInputStream to stream InputStream retrieved
from ResultSet directly.
     * The source stream is read twice, first for seeing whether source stream is/is not empty,
second for streaming it.
     * To keep reference to valid stream, EXTDTAInputStream have reference to resultset and
blob/clob also.
   * Modify master file of result  for blobclob4BLOB.
    * Now as same as result of embed driver, dead lock will be happen in clobTest92.
    * Different expected exception was happen in negative test in blobclob4BLOB.
Testing :
   Executed derbyall and found no error.

> Improve streaming of large objects for network server and client
> ----------------------------------------------------------------
>          Key: DERBY-326
>          URL: http://issues.apache.org/jira/browse/DERBY-326
>      Project: Derby
>         Type: Improvement
>   Components: Network Server, Network Client, Performance
>     Reporter: Kathey Marsden
>     Assignee: Tomohito Nakayama
>  Attachments: DERBY-326.patch
> Currently the stream writing  methods in network server and client require a  length
parameter. This means that we have to get the length of the stream before sending it. For
example in network server in EXTDTAInputStream we have to use getString and getbytes() instead
of getCharacterStream and getBinaryStream so that we can get the  length.
> SQLAM Level 7 provides for the enhanced LOB processing to allow streaming without indicating
the length, so, the writeScalarStream methods in
> network server DDMWriter.java and network client Request.java can be changed to not require
a length.
> Code inspection of these methods seems to indicate that while the length is never written
it is used heavily in generating the DSS. One strange thing is that it appears on error, the
stream is padded out to full length with zeros, but an actual exception is never sent.  Basically
I think perhaps these methods need to be rewritten from scratch based on the spec requirements
for lobs.
> After the writeScalarStream methods have been changed, then EXTDAInputStream can be changed
to properly stream LOBS. See TODO tags in this file for more info.  I am guessing similar
optimizations available in the client as well, but am not sure where that code is.

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