Thursday Jul 09, 2009

Swat Analyze function and Java heap problems, continued

If you read my earlier blog about java heap problems with Analyze, here is an other change that you can make, but it has some risks.

Swat Analyze by default keeps the last 180 seconds worth of i/o detail in memory. This is done so that Swat can identify any i/o that takes up to 180 seconds (180 sounds high, but I have seen them). If you know for sure that you do not have any i/o taking longer than for instance 30 seconds, you can change this 180 second value.

When using the GUI, select the 'Settings' tab, click on the 'batch_prm' line, add '-a30' (don't add the quotes), click 'Save', and restart Analyze.

If you can't use the GUI, go to file 'options.sUSERID.ini' and manually change the value after 'batch_prm' to '-a30' and restart Analyze. 

Note though that then any i/o lasting longer than 30 seconds will NOT be recognized by Swat.

Swat Analyze function and Java heap problems (OutOfMemoryError)

The default Java heap size given to Swat Analyze is -Xmx1024m (this is hardcoded, and is not to be confused with the heap size specified in the swat and swat.bat scripts).

For long traces and/or when you have lots of luns, 1024m may not always be enough. Could I increase the default? Technically, yes. However, for users that do not have much memory or swap space that could mean that they then can not even run the Swat Analyze at all. 1024m therefore is a decent starting value.

When your Analyze fails with 'java.lang.OutOfMemoryError: Java heap space', ignore the suggestion in  message 'Rerun as 'java -Xmx512m...', since that though technically is correct, is not complete enough. Changing the swat/swat.bat scripts also will not solve this.

When using the GUI, select the 'Settings' tab, click on the 'java_prm' line, increase the -Xmx value (the highest I have been able to do is -Xmx2560m), click 'Save', and restart Analyze.

If you can't use the GUI, go to file 'options.sUSERID.ini' and manually change the value after 'java_prm' and restart Analyze. 


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Blog for Henk Vandenbergh, author of Vdbench, and Sun StorageTek Workload Analysis Tool (Swat). This blog is used to keep you up to date about anything revolving around Swat and Vdbench.

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