Intel AS/400 RISC Server, 170 Servers, 7xx Servers manual

7.Full text indexes

Consider whether to allow users to create full text indexes for their mail files, and avoid the use of them whenever possible. These indexes are expensive to maintain since they take up CPU processing time and disk space.

8.Replication.

To improve replication performance, you may need to do the following: y Use selective replication

y Replicate more often so there are fewer updates per replication y Schedule replications at off-peak hours

y Set up replication groups based on replication priority. Set the replication priority to high, medium, or low to replicate databases of different priorities at different times.

9.Unread marks.

Select “Don’t maintain unread marks” in the advanced properties section of Database properties if unread marks are not important. This can save a significant amount of cpu time on certain applications. Depending on the amount of changes being made to the database, not maintaining unread marks can have a significant improvement. Test results in the lab with a Web shopping applications have shown a cpu reduction of up to 20%. For mail, setting this in the NAB decreased the cpu cost by 1-2%. Setting this in all of the user’s mail files showed a large memory and cpu reduction (on the order of 5-10% for both). However, unread marks is an often used feature for mail users, and should be disabled only after careful analysis of the tradeoff between the performance gain and loss of usability.

10.Don’t overwrite free space

Select “Don’t overwrite free space” in the advanced properties section of Database properties if system security can be maintained through other means, such as the default of PUBLIC *EXCLUDE for mail files. This can save on the order of 1-5% of cpu. Note you can set this for the mail.box files as well.

11.Full vs. Half duplex on Ethernet LAN.

Ensure the iSeries and the Ethernet switches in the network are configured to enable a full duplex connection in order to achieve maximum performance. Poor performance can result when running half duplex. This seems rather obvious, but the connection may end up running half duplex even if the i5/OS line description is set to full duplex and even if the switch is enabled for full duplex processing. Both the line description duplex parameter and the switch must be set to agree with each other, and typically it is best to use auto-negotiate to achieve this (*AUTO for the duplex parameter in the line description). Just checking the settings is usually not sufficient, a LAN tester must be plugged into the network to verify full vs. half duplex.

12.Transaction Logging.

Enabling transaction logging typically adds CPU cost and additional I/Os. These CPU and disk costs can be justified if transaction logging is determined to be necessary for server reliability and recovery speed. The redbook listed at the beginning of this chapter, “Domino for iSeries Sizing and Performance Tuning,” contains an entire chapter on transaction logging and performance impacts.

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
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