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Oracle Tips by Burleson |
OCP Instructors Guide for
Oracle DBA Certification
Chapter 7 - Tuning and Performance
High Water Mark and Table Scans
If all of the rows are being deleted, the administrator should use
the TRUNCATE statement to remove the unwanted rows. TRUNCATE
adjusts the high water mark to the first block in the segment. If a
partial purge is being performed, use the administrator must
reorganize the table with EXPORT/IMPORT or the ALTER TABLE MOVE
command.
Allocating too Much
Memory to the Shared Pool and Data Buffers
Maintaining high shared pool and data buffer
hit ratios is crucial for good database performance. Common
recommendations are to have the shared pool hit ratio above 98% and
the data buffer hit ratio above 95%.
The most common problem that occurs when too
much memory is allocated to the SGA is operating system memory
paging and swapping. Swapping and paging occurs when application
programs consume more memory than is currently available. The
operating system starts to transfer blocks of memory to swap space
on disk. If data in the swap space is needed, the operating system
transfers data from memory to the swap space to make room and moves
the needed data to memory (hence the term swap). All operating
systems have commands to monitor paging and swapping operations.
The above text is
an excerpt from:
OCP Instructors Guide for Oracle DBA Certification
A Study Guide to Advanced Oracle Certified Professional Database
Administration Techniques
ISBN 0-9744355-3-8
by Christopher T. Foot
http://www.rampant-books.com/book_2003_2_OCP_print.htm
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