tailieunhanh - oracle 8 database administration volume 1 instruction guide phần 6

Tham khảo tài liệu 'oracle 8 database administration volume 1 instruction guide phần 6', công nghệ thông tin, cơ sở dữ liệu phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | LGWR Log Switches and Checkpoints LGWR Log Switches and Checkpoints Oracle Architecture 7-5 Copyright Oracle Corporation 1998. All rights reserved. ORACLE Redo Log Buffer and the Background Process LGWR The Oracle Server sequentially records all changes made to the database in the redo log buffer. The redo log buffer is used in a circular manner. The redo entries are written to one of the online redo log groups called the current online redo log group by the LGWR process under the following situations When a commit occurs When the redo log buffer pool becomes one-third full When an LGWR timeout occurs every three seconds Before the DBWR writes modified blocks in the database buffers cache to the data files Log Switches LGWR writes to the online redo log files sequentially that is when the current online redo log group is filled LGWR begins writing to the next group. When the last available online redo log file is filled LGWR returns to the first online redo log group and starts writing again. Oracle8 Database Administration 7-7 Lesson 7 Maintaining Redo Log Files A log switch is the event during which LGWR stops writing to one online redo log group and starts writing to another. The database administrator can also force log switches see subsequent sections . Each time a log switch occurs and LGWR begins writing to a new log group the Oracle server assigns a number known as the log sequence number to identify the set of redo entries. When a log switch occurs an event called a checkpoint is initiated. Checkpoints During a checkpoint All dirty database buffers covered by the log being checkpointed are written to the data files by DBWR. The checkpoint background process CKPT updates the headers of all data files and control files to reflect that it has successfully completed. Checkpoints can occur for all data files in the database or for only specific data files. A checkpoint occurs for example in the following situations At every log switch When an instance has been

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