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Friday, September 25, 2015

Create and manage LOB segments

Create and manage LOB segments


Initializing Persistent LOBs to NULL or Empty

You can set a persistent LOB — ­that is, a LOB column in a table, or a LOB attribute in an object type that you defined— to be NULL or empty:

If a LOB column is initialized with EMPTY_CLOB() or EMPTY_BLOB(), then no LOB value exists, not even NULL. The row holds a LOB locator only. No additional LOB storage is used.


LOB storage characteristics that can be specified for a LOB column or a LOB attribute include the following:
  • TABLESPACE
  • PCTVERSION or RETENTION
  • Note that you can specify either PCTVERSION or RETENTION for BASICFILE LOBs, but not both. For SECUREFILE LOBs, only the RETENTION parameter can be specified.
  • CACHE/NOCACHE/CACHE READS
  • LOGGING/NOLOGGING
  • CHUNK
  • ENABLE/DISABLE STORAGE IN ROW
  • STORAGE

CHUNK

A chunk is one or more Oracle blocks




Setting a Persistent LOB to Empty



SHAIKDB>insert into dedup values (1,empty_blob());

1 row created.



SHAIKDB>create table lob1 (id number,desc1 blob)  lob(desc1) store as bfilelob (tablespace lobs chunk 4k pctversion 5 storage (maxextents 5));

Table created.




DBMS_LOB:

Overview

DBMS_LOB can read and modify BLOBs, CLOBs, and NCLOBs; it provides read-only operations for BFILEs. The bulk of the LOB operations are provided by this package.


Documentation:
a)Oracle® Database SecureFiles and Large Objects Developer's Guide
11g Release 2 (11.2)  Part Number E10645-01 → 11 LOB Storage


b)Oracle® Database PL/SQL Packages and Types Reference
11g Release 2 (11.2)
-- Part Number E10577-03 --> 79 DBMS_LOB

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