Oracle C++ Call Interface Programmer's Guide

Updating LOBs
LOB Classes and Methods
When to Use the getChunkSize() Method
Take advantage of the getChunkSize() methods of the Blob and Clob classes to
improve the performance of internal LOB read and write operations. The
getChunkSize() method returns the usable chunk size in bytes for BLOBs and in
characters for CLOBs and NCLOBs. When a read or write is done by using data
whose size is a multiple of the usable chunk size and starts on a chunk boundary,
performance improves. You can specify the chunk size for a LOB column when you
create a table that contains the LOB.
Calling the getChunkSize() method returns the usable chunk size of the LOB.
An application can batch a series of write operations until an entire chunk can be
written, rather than issuing multiple LOB write calls that operate on the same
chunk.
To read through the end of a LOB, use the read() method with an amount of 4 GB.
This avoids the round-trip involved with first calling the getLength() method
because the read() method with an amount of 4 GB reads until the end of the LOB
is reached.
Note: For LOBs which store varying width characters, the
GetChunkSize() method returns the number of Unicode
characters that fit in a LOB chunk.
When to Use the writeChunk() Method
OCCI provides a shortcut to make it more efficient to write data to the end of a
LOB. The writeAppend() methods of the Blob and Clob classes enables an
application to append data to the end of a LOB without first requiring a call to the
getLength() method to determine the starting point for a call to the write()
method.
The following code example demonstrates how to update an internal LOB (in this
example, a CLOB) to empty:
Clob clob(conn);
clob.setEmpty();
stmt->setSQL("UPDATE print_media SET ad_composite = :1
WHERE product_id=6666");
stmt->setClob(1, clob);
stmt->executeUpdate();
Introduction to LOBs 5-15