||Oracle Tips by Burleson
Chapter 7 Oracle Storage and Object
inline with other data if less than 4000 bytes in
length or in a special form of storage known as LOB storage if
greater than 4000 bytes in length. In most operating systems LOBs
can be up to 4 gigabytes in length if stored out-of-line using LOB
However, in order to ensure that proper
parameters have been used to set up the LOBs and LOB storage in your
database you must use two basic DBA views:
DBA_SEGMENTS - Information on lob segments used
in the database
DBA_LOBS - Information on lob storage areas.
An example report to show all lob segments not
owned by SYS or SYSTEM and several other default Oracle users is
shown below. You need to monitor LOB segments to be sure that:
1. The aren't collocated with base tables
2. They don't have excessive extents
These two items will prevent excessive IO
causing hot blocking in your base tablespace. Poor (read:default)
settings for LOB storage clauses will lead to bad LOB performance,
always tune LOB storage. Always provide a LOB storage clause for any
table using lobs in case the lob size exceeds 4000 bytes.
Copyright © 2003 by Rampant TechPress Inc.
The above text is
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