Shulou(Shulou.com)06/01 Report--

1. Configure RedoLog File

The configuration in the figure above has the following errors:

1. Asymmetric, Group3 has only one member, which causes write errors;

2. Multiple members of a group are placed on one disk, which not only causes the load of frequent writes to be concentrated on one disk, but also does not achieve disk redundancy and does not play the role of backup.

For configuration of online redo log files, the following recommendations are made:

1. With multiple groups of Redo LogFiles, each group has at least two members, and different members are placed on different disks (even if a member of a group is damaged, as long as one member is still normal, the database can still work normally). The specific number depends on the specific situation. If the data concurrency is large, the data of RedoLog File grows very fast, so it is necessary to allocate several groups, so as to ensure that the written data of RedoLog File can be archived and saved in time.

2. Online redo log files should not be placed on the same disk as archive files to avoid LGWR and ARCn operating on the same disk at the same time.

3. DataFile should not be placed on a disk with Redo Log File, for the same reason.

If the number of disks is relatively large, it is recommended that different group members be placed on different disks, that is, the members of the group and the group are evenly distributed to the disks. The same applies to Control File.

2. Apply OMF to manage Redo Log File

III. How to obtain group and group member information of online redo log

SQL> select * from v$logfile;

GROUP# STATUS TYPE MEMBER IS_---------------------------------------------------- ----------------- 3 ONLINE /oracle/oradata/orcl/redo03.log NO 2 ONLINE /oracle/oradata/orcl/redo02.log NO 1 ONLINE /oracle/oradata/orcl/redo01.log NO

SQL> select group#, thread#, members, archived, status from v$log;

GROUP# THREAD# MEMBERS ARC STATUS---------- ---------- ---------- --- ---------------- 1 1 1 NO INACTIVE 2 1 1 NO INACTIVE 3 1 1 NO INACTIVE 4 1 2 NO CURRENT

SQL> select * from v$log_history;

RECID STAMP THREAD# SEQUENCE# FIRST_CHANGE#FIRST_TIM NEXT_CHANGE#---------- ---------- ---------- ---------- ---------------------- RESETLOGS_CHANGE# RESETLOGS----------------- --------- 1 854822167 1 1 754488 05-AUG-14 788787 75448805-AUG-14 2 854822200 1 2 788787 05-AUG-14 792507 75448805-AUG-14 3 854823639 1 3 792507 05-AUG-14 802814 75448805-AUG-14

For more information on dynamic performance tables for online redo log files, see the online documentation Reference.

Thread concept in online redo log file

Thread is mainly used in RAC environments, i.e. multi-instance systems, where each instance can have its own thread.

Archived online redo log files

Archive mode ensures data recovery and supports hot backups. Databases default to non-Archive mode, but Archive mode is strongly recommended in production environments. The dynamic performance tables v$instance and v$database can be used to query whether the current database is in archive mode:

SQL> desc v$instance

Name Null? Type ------------------------------------------------- ------------------- INSTANCE_NUMBER NUMBER PARALLEL VARCHAR2(3) THREAD# NUMBER ARCHIVER VARCHAR2(7)… BLOCKED VARCHAR2(3)

SQL> select archiver from v$instance;

ARCHIVE-------STOPPED

SQL> desc V$database;

Name Null? Type ------------------------------------------------- ------------------- DBID NUMBER NAME VARCHAR2(9) PRIOR_RESETLOGS_TIME DATE LOG_MODE VARCHAR2(12)… SUPPLEMENTAL_LOG_DATA_PL VARCHAR2(3) MIN_REQUIRED_CAPTURE_CHANGE# NUMBER

SQL> select log_mode from v$database;

LOG_MODE------------NOARCHIVELOG

ARCn This process reads the online redo log file and writes it to the archive file. After archiving, a corresponding record will be added to the controlfile.

In non-Archive mode, online redo log files can only be reused after a checkpoint occurs; in Archive mode, in addition to checkpoints, you need to ensure that the file has been archived by ARCn before Redo Log Files can be reused.

Archived online redo log files can also be multiplexed.

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