The db file scattered read wait event is similar to the db file sequential read, except that the session is waiting for a multi-block I/O read request to complete. The db file scattered read waits are...
How to Identify a Buffer Cache Chain Latch Problem Internally, Oracle uses various types of structures to control access to elements of the databases including latches and various types of enqueuein...
A direct path read I/O operation reads data into the session's PGA instead of the SGA. Direct read I/Os may be performed in synchronous or asynchronous mode, depending on the platform and the value of...
This wait event only occurs when Flashback Database is turned on. A session waits for recovery writer (RVWR) to write flashback data to the flashback logs on disk because the buffers are full. Until R...
Identify Contention The following query determines the miss ratio and the "immediate" miss ratio for redo log latches. Col MISS_RATIO format 999.99Col IMM_MISS_RATIO format 999.99 SELECT substr(ln.na...
Row chaining occurs when a row can't physically fit into an Oracle block. Another block is required to store the remainder of the row. Chaining can cause serious performance problems and is especially...
Oracle provides statistics which relate to the capability of rollbacks to shrink back to an optimal size. To make use of these statistics it is suggested that the following two views be created to red...
Shared pool latch contention can occur when the shared pool is sized too large to be effectively managed. Starting with Oracle version 8.1.6, Oracle implemented improved shared pool management archite...
Just as the architecture of the database buffer cache has changed dramatically from release to release, so too have the effectiveness of the tools Oracle supplies to assist with tuning the database bu...
The Parallel Query Option (PQO) is best used for systems where large, intense queries are being performed or where large amounts of data are being loaded, indexed and queried, such as in data warehous...
Processing SQL Statements The first time a select query is executed inside the Oracle engine, the statement will generally need to proceed through 4 different stages in order to return results back to...
Sometimes, data blocks are read in the database, and are infrequently reused. Often in a database we also have data blocks that are of frequent use (hot blocks). It is for these types of database bloc...
