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

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The "db file sequential read" wait event occurs when a session is waiting for a single data block to be read from disk into the buffer cache in a sequential manner. This wait event is common when a query or operation requires access to a specific data block that is not currently in memory. Explanation: This wait event indicates that a session is waiting for the I/O operation to complete, bringing the requested data block into memory. It usually occurs during SELECT operations or when an index is being accessed. It's a normal part of database operations, especially in OLTP systems where individual data blocks are frequently accessed. 

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

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SELECT SID, SERIAL#, WAIT_CLASS, EVENT, WAIT_TIME, SECONDS_IN_WAIT
FROM V$SESSION
WHERE EVENT = 'db 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;

Query to identify sessions waiting on the "db file sequential read" wait event along with the correct columns:

SELECT EVENT, WAIT_CLASS_ID, WAIT_CLASS#, WAIT_CLASS, P1TEXT, P1, P2TEXT, P2, P3TEXT, P3
FROM V$SESSION_WAIT
WHERE EVENT = 'db file sequential read';

Resolution: 

 Optimize Queries: Ensure that queries are well-tuned and avoid unnecessary full table scans. Proper indexing and efficient query design can reduce the occurrence of sequential reads. 

 Increase Buffer Cache: Increasing the size of the buffer cache can help keep frequently accessed data blocks in memory, reducing the need for sequential reads. 

 Consider Faster Storage: If the storage system is slow, consider upgrading to faster storage technologies or optimizing disk I/O. 

 Partitioning: Partitioning large tables can reduce the impact of sequential reads by minimizing the number of rows read. 

 Use Direct Path Reads: For large data loads, consider using direct path reads to load data directly into the buffer cache. 

 Use Parallelism: Utilize parallel processing for queries that perform large sequential reads. 

 Consider Exadata Storage: If available, Oracle Exadata storage offers features that can reduce the impact of sequential reads. 

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

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