Log file sequential read Wait Event , Cause, Related SQL queries, Possible Resolution

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The "log file sequential read" wait event occurs when a session is waiting for a single redo log file block to be read from disk into the buffer cache in a sequential manner. This wait event is common during log file access operations, such as reading redo log records during recovery or archive log processing. 

 Explanation: During database operations, especially during recovery processes, Oracle may need to read specific redo log records stored in redo log files on disk. 

The "log file sequential read" wait event indicates that a session is waiting for an I/O operation to complete, bringing the requested redo log block into the buffer cache.

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Queries: Identifying Sessions with "log file sequential read" Wait Event:

SELECT SID, SERIAL#, EVENT, WAIT_TIME, SECONDS_IN_WAIT
FROM V$SESSION
WHERE EVENT = 'log file sequential read';

Identifying Top Wait Events in the Database:

SELECT EVENT, TOTAL_WAITS, TIME_WAITED_MICRO/1000000 AS SECONDS_WAITED
FROM V$SYSTEM_EVENT
ORDER BY TOTAL_WAITS DESC;

Resolution: 

 I/O Performance: Monitor the I/O performance of the storage subsystem where redo log files are stored. Ensure that it can efficiently handle read operations. 

 Buffer Cache Size: Adequately size the buffer cache to retain frequently accessed redo log blocks in memory, reducing the need for sequential reads. 

 Optimize Redo Log Configuration: Review the redo log configuration, including the number of redo log groups, members, and size. A well-configured redo log can minimize sequential reads. 

 Storage Optimization: Use high-performance storage solutions for redo log files to reduce the time taken for sequential reads. 

 Review Archiving and Recovery Processes: Ensure that archive log processing and recovery operations are optimized to minimize the need for sequential reads. 

 Batch Recovery Operations: When performing recovery or archive log processing, batch related operations together to minimize sequential reads. 

 Monitor and Analyze: Continuously monitor the database performance using tools like Oracle Enterprise Manager or other monitoring solutions to identify and address performance issues. 

 Query Tuning: If sequential reads occur during query execution, consider query tuning to reduce the need for reading large amounts of redo log data. 

 Consider Solid-State Drives (SSDs): SSDs can significantly improve read performance for redo log files. 

 Remember that the "log file sequential read" wait event is typically associated with specific database operations like recovery or archive log processing. Properly configuring and monitoring the storage subsystem, buffer cache, and overall system performance are essential for minimizing the impact of this wait event.

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