RAC Wait Event Enhancements in Oracle Database 10g

RAC Wait Event Enhancements in Oracle Database 10 g

Starting from Oracle Database 10 g , most of the RAC related wait events could be further classified into two types: place holder events and fixup events. For example, when a CR request is initiated, the outcome can be either a lock grant or a buffer. In other words, when a session is looking for a block in the global cache, it may not know whether it will get a buffer cached at remote instance or receive a lock grant to read the block from disk. The wait events tell precisely whether the session is waiting for a lock grant or buffer to arrive from other instance cache. This detailed breakup information is not available in previous versions because the complete wait time is charged to a single wait event. In the preceding example, the global cache cr request wait is a placeholder event. The outcome of the wait event (which could be another wait, such as a receiving message to read the block from disk) is called a fixup event. Here is a brief listing of fixup wait events and their categories:

• Block-oriented

  • gc current block 2-way

  • gc current block 3-way

  • gc cr block 2-way

  • gc cr block 3-way

• Message-oriented

  • gc current grant 2-way

  • gc cr grant 2-way

• Contention-oriented

  • gc current block busy

  • gc cr block busy

  • gc current buffer busy

• Load-oriented

  • gc current block congested

  • gc cr block congested

Note ‚  

The fixup events are for informative purposes; thus there isn ‚ t much to do in the way of tuning, nor has there been anything written about them in the Oracle documentation. These events merely provide additional details about the block and message transfers, and knowing them will help you understand the behavior of the resources used in the database.