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The redo log buffer, usually less than a couple of megabytes in size, and thus nowhere near the size of the database buffer cache and the shared pool cache, is nonetheless a crucial component of the SGA. When a server process changes data in the data buffer cache (via an insert, a delete, or an update), it generates redo data, which is recorded in the redo log buffer. The log writer process writes redo information from the redo log buffer in memory to the redo log files on disk.

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Another use of the proc file system is to influence the running system by modifying the files located in /proc. A simple example is the system name found in /proc/sys/kernel/ hostname; by redirecting a new name into this file, you would end up overwriting the previous entry, thus changing the system name. You can view the change by using the uname -n command. The change lasts only until your next reboot, as the system-configuration files still hold the system s original name. Other system attributes can be modified in the same way, such as RAID rebuild rates and the way the system handles swap or power-management settings. Bear in mind, however, that the power to modify system settings is dangerous. You might cause the system to hang or even to crash. It would be wise to perform extensive testing on noncritical machines before implementing environment-wide modifications.

You use the LOG_BUFFER initialization parameter to set the size of the redo log buffer, and it stays fixed for the duration of the instance That is, you can t adjust the redo log buffer size dynamically, unlike the other components of the SGA The log writer process writes the contents of the redo log buffer to disk under any of the following circumstances: The redo log buffer is one-third full Users commit a transaction The database buffer cache is running low on free space and needs to write changed data to the redo log The database writer instructs the log writer process to flush the log buffer s contents to disk to make room for the new data.

The redo log buffer is a circular buffer the log writer process writes the redo entries from the redo log buffer to the redo log files, and server processes write new redo log entries over the entries that have been written to the redo log files You only need to have a small redo log buffer, about 1MB or so Large redo log buffers will reduce your log file I/O (especially if you have large or many transactions), but your commits will take longer as well The log writer process usually writes to the redo log files very quickly, even when its workload is quite heavy You ll run into more problems if your redo log buffer size is too small than if it is too large A redo log buffer that is too small will keep the log writer process excessively busy it will be constantly writing to disk.

Furthermore, if the log buffer is too small, it will frequently run out of space to accommodate new redo entries Oracle provides an option called nologging that lets you bypass the redo logs almost completely and thus avoid contention during certain operations (such as a large data load) You can also batch the commits in a long job, thus enabling the log writer process to more efficiently write the redo log entries..

The large pool is a purely optional memory pool, and Oracle manages it quite differently from the shared pool. Oracle uses the large pool mostly for accommodating Recovery Manager (RMAN) operations. You set the size of this pool in the initialization file by using the LARGE_POOL_SIZE parameter. The large pool memory component is important if you re using the shared server architecture. The Java pool (set by using the JAVA_POOL_SIZE parameter) is designed for databases that contain a lot of Java code, so that the regular SGA doesn t have to be allocated to components using Java-based objects. Java pool memory is reserved for the Java Virtual Machine (JVM) and for your Java-based applications. The default size for this memory pool is 20MB, but if you re deploying Enterprise JavaBeans or using CORBA, you could potentially need a Java pool size greater than 1GB.