Analyzing Top Wait Events in Oracle

Introduction
Understanding Wait Events
The SQL Query
Explanation of the Script
Analyzing the Results
Conclusion

Introduction

In Oracle Database, wait events are a key indicator of performance issues. By analyzing wait events, database administrators can identify bottlenecks and optimize system performance. This blog will guide you through the process of identifying top wait events using a specific SQL script, breaking down the query, and analyzing the results.

Understanding Wait Events

Wait events occur when Oracle processes are delayed waiting for resources or conditions. These events are categorized into classes like 'User I/O', 'System I/O', and 'Concurrency'. Monitoring wait events helps in pinpointing performance issues, such as slow I/O operations or locking problems, allowing DBAs to take corrective actions.

The SQL Query

To identify the top wait events in Oracle, use the following SQL script. This script retrieves data from system views, calculates the time spent on each event, and displays the results in a readable format. 

select
    name,
    round(time_secs, 2) time_secs,
    case when time_secs = 0 then
        0
    else
        round(time_secs*100 / sum(time_secs) Over(), 2)
    end pct
from
    (
        select
            e.event Name,
            e.time_waited / 100 time_secs
        from
            v$system_event e
            join
            v$event_name n
                on n.name = e.event
        where
            n.wait_class <> 'Idle'
        and
            time_waited > 0

        union

        select
            'server CPU',
            sum(value / 1000000) time_secs
        from
            v$sys_time_model
        where
            stat_name in ('background cpu time', 'DB CPU' )
    )
order by
    time_secs desc;
Oracle wait events

Explanation of the Script

This script performs the following tasks:
  • Selects wait event details from v$system_event and v$event_name, excluding idle events.
  • Calculates the time waited for each event, converting centiseconds to seconds.
  • Includes CPU time from v$sys_time_model to provide a complete picture of wait times.
  • Combines the results using a UNION operation and orders by total time waited.
  • Calculates the percentage of total wait time for each event.

Analyzing the Results

Once you run the query, you'll get a list of top wait events along with the time spent on each and their percentages of the total wait time. Here's how to interpret the results:
  • Event Name: The specific event the database is waiting on.
  • Time (seconds): The total time spent waiting for the event, rounded to two decimal places.
  • Percentage (%): The proportion of the total wait time that the event represents.
Key Points to Focus On - High Wait Times: Events with the highest `time_secs` and `pct` indicate major performance bottlenecks.
- CPU Utilization: High 'server CPU' time suggests CPU-intensive processes, which may need optimization.
- Specific Wait Events: Events like 'db file sequential read' or 'log file sync' often indicate I/O or commit issues, respectively.

Conclusion

Monitoring and analyzing wait events in Oracle Database is essential for maintaining optimal performance. By using the provided SQL script, you can identify where the database spends most of its waiting time and address these issues effectively. Regular analysis of wait events helps in proactive database management, ensuring a smooth and responsive database environment. Understanding and resolving wait events will lead to faster query execution and a more efficient Oracle Database, ultimately benefiting your overall system performance.

Related content



Rate Your Experience

: 89 : 1


Last updated in July, 2024

Online Tests
Read more

Cloud Technology
Read more

Oracle Database
Read more

MSSQL Database
Read more

PostGres Database
Read more

Linux
Read more

ASP/C#
Read more

Quick Access

All Rights Reserved @2024 | www.dbdocs.net | Privacy Policy | Disclaimer | Cookie Policy