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SQL Performance Diagnosis: High I/O Wait Time

Avatar photoCustomer Questions & Answers 5 replies

When using the DBA AWR SQL Performance Summary, which metric should I focus on to identify SQLs specifically bottlenecked by reading/writing data (I/O)?

5 replies

  • Support Enginatics

    Focus on the ‘User Io Wait Time’ column. This shows the total elapsed time in seconds from the wait event class ‘User I/O’.

  • Avatar photoCustomer

    The default sorting shows the most CPU-intensive SQLs first. If I want to prioritize tuning IO-bound queries or network issues, how should I sort the data?

  • Support Enginatics

    If tuning server load is the goal, CPU is usually prioritized, but if you want to spot other bottlenecks like IO or network waits (e.g., ‘SQL*Net message from dblink’), you should sort the report by ‘elapsed time’ instead of CPU time.

  • Avatar photoCustomer

    If I notice high IO, should I also investigate table modification tracking?

  • Support Enginatics

    Yes, tracking table modifications can be useful for performance context. You can use the DBA Table Modifications report to see the number of rows modified since the last analysis, provided table monitoring is active.

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