Oracle Metric multiblock read objects Oracle Consulting Tips by Burleson

The multiblock read objects Oracle metric latch protects the allocation and release of multi block read objects from the SGA.  Multi-block reads are a form of sequential prefetch invoked by Oracle for large-table full scans (i.e. index fast-full scans) and are dependent on the settings for db_file_multiblock_read_count. 

10gr2 Note:  Starting in Oracle 10g release2, Oracle recommends not setting the db_file_multiblock_read_count parameter, allowing Oracle to empirically determine the optimal setting.  For more see my notes on 10gR2 automatically tuned multi-block reads.

The maximum effective setting for db_file_multiblock_read_count is OS and disk dependant. Steve Adams, an independent Oracle performance consultant (see www.ixora.com.au ), has published a helpful script to assist you in setting an appropriate level.  This script conducts a test and sample actual I/O chunk sizes on your server to aid you in setting db_file_multiblock_read_count:

http://www.ixora.com.au/scripts/sql/multiblock_read_test.sql

Here are my notes on multiblock reads in Oracle:

Tuning multi-block I/O in Oracle

Oracle wait tuning with v$session_wait

Oracle db file sequential scattered read disk I/O speed tuning

Oracle index_ffs hint & optimizer_mode

Oracle multiple block size Data Warehousing Architectures

Oracle db file scattered

     
This, and many other Oracle performance metrics are discussed in my book "Oracle Tuning" by Rampant TechPress.  You can buy it directly from the publisher and save 30% at this link:

http://www.rampant-books.com/book_1002_oracle_tuning_definitive_reference_2nd_ed.htm