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In today’s article, we will be cover about the features of the Database Buffer Cache, the largest memory area in the SGA.<\/p>\n
\u2022 The most important task of this area is to optimize the amount of physical I\/O.<\/p>\n
\u2022 Data blocks in the Data file that are usually read by users are kept in this area.<\/p>\n
\u2022 Oracle searches the queried data in this area before going to the data files in the physical disk space.<\/p>\n
If the queried data has been queried by another user before, Oracle transmits the data to the user from this field.<\/p>\n
\u2022 If users perform DML operations such as update or insert, the changed data blocks are written to this area before the data files on the physical disk.<\/p>\n
These data blocks that change in the buffer area are called “Dirty Blocks”.<\/p>\n
Dirty Block; These are database blocks that have been changed by the user, written to the database buffer cache, and not yet written to the data files on the disk.<\/p>\n
The database marks these blocks with a “checkpoint” before using them.<\/p>\n
These blocks are called “Clean Blocks” after they are written to the data files on the disk.<\/p>\n
\u2022 Blocks used by any user in the database are pinned to memory.<\/p>\n
The session using the pinned blocks can modify these blocks.<\/p>\n
Not all sessions can change the pinned block at the same time.<\/p>\n
\u2022 The DBW(n) background process carries out the communication between the Database Buffer Cache and data files.<\/p>\n
\u2022 Database Buffer Cache is emptied with the following command.<\/p>\n
In this case, dirty blocks are saved to data files with the DBW(n) process.<\/p>\n
\u2022 LRU (least recently used) algorithm runs in the database buffer cache.<\/p>\n
The least used data is deleted from the buffer cache and the most used data is preserved.<\/p>\n