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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

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