How often should redo logs switch?
How often should redo logs switch?
A good rule of thumb is to switch a redo log every 20 to 30 minutes. Listing 1 gives a SQL statement that will show how often log file switching is occurring every hour. You need only increase your redo log sizes to hold more redo and this will reduce the amount of log file switching.
How many redo log groups should I have?
An instance requires at least two groups of redo log files, regardless of the number of members in the groups. (A group comprises one or more members.) You can drop a redo log group only if it is inactive. If you need to drop the current group, first force a log switch to occur.
How do I know the size of my redo log?
You can view the redo_buffer_allocation_retries in V$SYSSTAT to see if your redo log files are too small. There are two ways to see the frequency of log switches, the v$loghist view and looking at the Oracle alert. log.
What is redo log switch?
A log switch is the point at which the database stops writing to one redo log file and begins writing to another. Normally, a log switch occurs when the current redo log file is completely filled and writing must continue to the next redo log file.
What is Archive_lag_target?
ARCHIVE_LAG_TARGET limits the amount of data that can be lost and effectively increases the availability of the standby database by forcing a log switch after the specified amount of time elapses. A 0 value disables the time-based thread advance feature; otherwise, the value represents the number of seconds.
What is V Log_history?
V$LOG_HISTORY displays log history information from the control file.
How do you multiplex a redo log file?
To multiplex your redo log, you must add members to each redo log group. It is not required that redo log groups be symmetrical, but Oracle recommends that your groups all have the same number of members. A database must have a minimum of two redo log groups.
How do you increase a redo log?
Use the following steps to update redo log size and files:
- Log in to the database node/VM (rp2vm2) as oracle user.
- Connect to sqlplus.
- Update redo log file size and increase groups using the steps captured below.
- Switch the log file to the newly added redo log groups and delete the old inactive groups.
How do I read a redo log in Oracle?
LogMiner retrieves information from those redo log files and returns it through the V$LOGMNR_CONTENTS view. You can then use SQL to query the V$LOGMNR_CONTENTS view, as you would any other view. Each select operation that you perform against the V$LOGMNR_CONTENTS view causes the redo log files to be read sequentially.
What is PGA and SGA in Oracle?
System global area (SGA)—A shared memory area that contains data buffers and control information for the instance. The SGA is divided into separate buffer areas and data pools. These are described in “SGA Components”. Program global area (PGA)—A memory area used by a single Oracle server process.
How do you force a log switch?
To force a log switch, you must have the ALTER SYSTEM privilege. Use the ALTER SYSTEM statement with the SWITCH LOGFILE clause.
What is V Archived_log?
V$ARCHIVED_LOG displays archived log information from the control file, including archive log names. An archive log record is inserted after the online redo log is successfully archived or cleared (name column is NULL if the log was cleared).
How do I add a logfile group in RAC?
Steps to add redo log groups to Oracle RAC setup
- Check existing redo log groups & redo log file size. SQL> column REDOLOG_FILE_NAME format a50; SQL> set lines 1000.
- As we checked redo log file location & size, we will proceed for redo log group addtions.
- Check for newly added redo log groups:
What is thread in Oracle RAC?
THREAD is a Real Application Clusters parameter that specifies the number of the redo thread to be used by an instance. When you create a database, Oracle creates and enables thread 1 as a public thread (one that can be used by any instance).
How do I increase the redo log size in RAC?
Resize the redo log file in RAC Environment as follows:
- Check the size of redo log and how many redo log file present in each instance.
- Check the thread information if you needed which thread belong to which instance.
- Retrieve all the information of member and location.
- You want to increase the size of redo log files.
How do I resize a redo log in standby database?
Following are the steps to drop and create new standby database:
- Check Primary Redo Thread Number and size.
- Check Standby Thread number and Size for Standby redo logs.
- Stop the data-guard recovery process in Standby database:
- Drop the existing Standby redo files:
- Create new Standby logfile with THREAD Clauses.
What is difference between archive and redo log?
Archive logs are archived redo(online) log files. In redo log files are all changes that happened to your data. If your database is in archivelog mode, than redo logs can’t be overwritten, they are archived in some other location when they are full. Redo and archive logs are used in various database recovery scenarios.
What is the main drawback of redo logging?
An example disadvantage of redo logging is that all modified blocks must be kept in buffers until the transaction commits and the log records have been flushed. Both cause problems if one has a block in memory that was modified by a transaction that is ongoing and modified by a transaction that has committed.
What is Pfile and Spfile?
SPFILE is a binary file that contains the same information as the old PFILE. SPFILE permits dynamic changes without requiring you to restart that instance. By default, if you do not specify PFILE in your STARTUP command, Oracle will use server parameter file (SPFILE).
What is the difference between Pmon and Smon?
PMON and SMON are two required background processes. PMON is the Process Monitor which is responsible for recovering processes when the user process fails. PMON does the process cleanup. SMON is the System Monitor which is responsible for recovering the system after a failure.