ORACLE ENQUEUE WAITS FOR FREE
ORACLE ENQUEUE WAITS FULL

When a query is running slow, it usually means that there are excessive waits of one type or another.

Log file sync: These are waits by server processes that are performing a commit (or rollback) for the LGWR to complete its write to the redo log file.Īnalyzing Oracle wait events is the starting point when troubleshooting a slow-running query.

ORACLE ENQUEUE WAITS FOR FREE

Log buffer space: These are waits caused by server processes waiting for free space in the log buffer.

You actually won’t see a wait event named enqueue (or enq) because the enqueue wait event types are always held for a specific purpose, such as enq: TX – contention, enq:TX – index contention, and enq:TX – row lock contention.

Enqueue waits: These are waits on Oracle locking mechanisms that control access to internal database resources and that occur when a session waits on a lock held by another session.

The reads are single block reads and are usually because of indexed reads.

Db file sequential read: These are waits incurred by an user process for a physical I/O to return when reading buffers into the SGA buffer cache.

ORACLE ENQUEUE WAITS FULL

The scattered reads are multiblock reads and can occur because of a full table scan or a fast full scan of an index. Db file scattered read: These are waits incurred by an user process for a physical I/O to return when reading buffers into the SGA buffer cache.Free buffer waits: These waits occur when a server process posts the database writer process to write out dirty buffers in order to make free buffers available.Buffer busy waits: These occur when multiple processes attempt to concurrently access the same buffers in the buffer cache.Although there’s a large number of wait events, some the most common wait events are the following: For example, a SQL statement may be modifying data, but the server process may have to wait for a data block to be read from disk because it’s not available in the SGA. Wait events are statistics that a server process or thread increments when it waits for an operation to complete in order to continue its processing. TOP Interview Question : Explain Brief Top 5 Wait Events ? Analyzing Wait Events :

Oracle enqueue waits