Dataguard- scheduling manual log switch to have minimal lag

Hi,
I need some suggestion..
Recentry I had configured a physical standby for my 10g production database in maximum performance mode.
Now , to reduce the lag between the primary and standby , I put one cron job which will do a manual log switch(alter system switch logfile) in every 30 minutes.
and it is doing the job..!
Does this have any impact on my databases...?
Looking forward for your invaluable responce...
Regards
Noushad
DBA

Maybe you should let Oracle do it's job, configure this parameter which signifies that no buffer will remain dirty (in the cache) for more than 1800 (or whatever you want) seconds:
LOG_CHECKPOINT_TIMEOUT = 1800:p

Similar Messages

Is there a way to identify manual log switches?

Hi!
A while ago I upgraded a 10g database to 11.2.0.2 64 Bit Windows.
During the Upgrade we realized that redo logs were configured really small (~10MB) what resulted in a lot of log switches (a few hundred per day). So we adjusted redo log size to 100MB and set archive_lag_target to 1800.
The amount of log switches went down a little but less far than we expected it. After further analysing the situation we recognized that Oracle is switching logs far before reaching the 100MB log size (and also far before reaching 1800s). All the archived logs have a size of about 15MB. I know that 11g invented something like "preemptive log switching" that switches logs round about 20% before reaching the maximum value (if I remember it correctly..). But switching already at 15% of the maximum size seems strange to me...
I couldn't find any helpful stuff on Google or Metalink about that topic but today I had a different idea: what if it's the application software that's doing manual log switches?
(I have no idea why it should do that but I can remember that the application user does require the sysdba privilege - don't ask me why, I didn't write it, I won't defend it...)
So I checked the alert log but unfortunately I had to realize that there is no difference between an automatic switch and a manual one (only alter system archive log... does get an extra line).
So my questions are:
1) Does anybody know a way of distinguishing between an automatic log switch and a manual one? Is there a table or another logfile where this information is recorded?
2) Has anybody experienced a similar situation where Oracle is switching the logs way before reaching the maximum size?
Best regards,
Marcus

lebigmac wrote:
1) Does anybody know a way of distinguishing between an automatic log switch and a manual one? Is there a table or another logfile where this information is recorded?
Off the top of my head - I think the only way to do a manual log switch is to issue "alter system switch log file", and I think that any "alter system" command is written to the alter log in you version of Oracle. (I really ought to check both statements before posting this, but I've been up since 2:30 am).
2) Has anybody experienced a similar situation where Oracle is switching the logs way before reaching the maximum size?
It's very common with recent versions of Oracle when private redo threads come into play; but your example seems a little exaggerated. The log file switch has to start when there is enough space left in the log file for all the public and all (or maybe it's the previously used - i'll have to check my book) private redo threads. You could check x$kcrfstrand to see what this sizes look like: http://jonathanlewis.wordpress.com/?s=private+thread
Regards
Jonathan Lewis

Log Switch during RMAN backup

I have seen in many RMAN backup scripts that a manual log switching is performed in first line of the script? What is it purpose, just to write changes needed to reconstruct the DML/DDL statements to online redo logfiles and start the archiving process if db is running in archive log mode?

918868 wrote:
I have seen in many RMAN backup scripts that a manual log switching is performed in first line of the script? What is it purpose, just to write changes needed to reconstruct the DML/DDL statements to online redo logfiles and start the archiving process if db is running in archive log mode?That could be the only reason but even that is not needed as RMAN would do a log switch automatically to push the current redo log file to make it's archive log and include it in the backup.
Aman....

Dataguard log switch question

Wonder if anyone can help me with a question?
I am new to data guard and only recently setup my first implementation of a primary and standby Oracle 11 g database.
It's all setup correctly, i.e no gaps sequences showing, no errors in the alert logs and I have successfully tested a switch over and switch back.
I wanted to re-test the archive logs were going across to the standby database ok, unfortunately I performed an alter system switch logfile on the standby database instead of primary.
No errors are reported anywhere, no archive log sequence gaps or errors in the alert logs, but I am wondering if this will cause a problem the next time I have to failover to the standby database?
Apologies for my lack of my knowledge I am new data guard and only been a DBA for a couple of years, have not had time to read up on the 500 page Data Guard book yet.
Thanks in Advance

First you have to know what happens when log switch occurs either manually or internally.
All data & changes will be in online redo log files, once log switch occurred either automatic or forcefully, these information from online redo log files will be dumped to archives.
Now tell me. Where will be the online redo? There is no concept of online redo data on standby, in case of real time apply you will have only standby redo log files, even you cannot switch standby redo log files.
First this command on standby won't work, it's applicable only for online redo log files. So onions redo exists/active only in primary.
So nothing to worry on it. Make sure environment is sync prior to performing switchover.
Hope this helps.
Your all questions why unanswered? Close them and keep the forum clean.

Database log switch and WLS connection pool relation

Hi,
We have been facing WLS JDBC connection pool disable and suspension issue very frequently in our environment and as a work around have implemented multi-datasource configuration (fail over method).
But we need to know the root cause for the same and want to fix the issue too.
We have tried many options like increasing no. of processes and transaction on Database, fine tune the weblogic datasource but still we could not isolate the issue.
Recently we have been advised to minimize the log switch on database front and increase the redo log size. Not sure if this will help in isolating the issue or not.
So we are Looking forward for the comments and suggestions on what would be the relationship b/w datasource and log switch be and if someone have faced this issue and resolved the same by fine tuning the database and minimizing the log switch.
We are using WLS 10.3.3.0
-Rohit

turn on jdbc logging. The server log should be showing the troubles WLS is having
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Log switch checkpoint

Hello
Assume I have two redologs.
Log1-->current
Log2->inactive
After log switch, it becomes.
log1 -->active
log2-->current
The thing is after log switch; checkpoint must be issued and the log1 should be inactive. Why does it show active?
If I manually issue
"alter system checkpoint"
Log1 becomes inactive immeidately.

Mathias Delgado wrote:
Mr sb;
I have also read some other docs.
Please confirm wheter my understanding is correct.
After alter system switch logfile, checkpoint is initiated, not finished.
However when I issue,
"alter system checkpoint"
Checkpoint is issued immediately and therefore the status is of redolog is changed from active to inactive immediately.No , your understanding is incorrect.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
SQL> select * from V$log;
    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARC STATUS
FIRST_CHANGE# FIRST_TIM
         1          1         65   52428800          1 YES INACTIVE
      2254888 25-JUN-09
         2          1         66   52428800          1 YES INACTIVE
      2279864 26-JUN-09
         3          1         67   52428800          1 NO CURRENT
      2300530 27-JUN-09
SQL> select checkpoint_change# from V$datafile;
CHECKPOINT_CHANGE#
           2300531
           2300531
           2300531
           2300531
           2300531
           2300531
           2300531
           2300531
8 rows selected.
SQL> alter system checkpoint;
System altered.
SQL> select checkpoint_change# from V$datafile;
CHECKPOINT_CHANGE#
           2302787
           2302787
           2302787
           2302787
           2302787
           2302787
           2302787
           2302787
8 rows selected.
SQL> select * from V$log;
    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARC STATUS
FIRST_CHANGE# FIRST_TIM
         1          1         65   52428800          1 YES INACTIVE
      2254888 25-JUN-09
         2          1         66   52428800          1 YES INACTIVE
      2279864 26-JUN-09
         3          1         67   52428800          1 NO CURRENT
      2300530 27-JUN-09
SQL> alter system checkpoint;
System altered.
SQL> select * from V$log;
    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARC STATUS
FIRST_CHANGE# FIRST_TIM
         1          1         65   52428800          1 YES INACTIVE
      2254888 25-JUN-09
         2          1         66   52428800          1 YES INACTIVE
      2279864 26-JUN-09
         3          1         67   52428800          1 NO CURRENT
      2300530 27-JUN-09
SQL> select checkpoint_change# from V$datafile;
CHECKPOINT_CHANGE#
           2302798
           2302798
           2302798
           2302798
           2302798
           2302798
           2302798
           2302798
8 rows selected.
SQL> alter system switch logfile;
System altered.
SQL> select checkpoint_change# from V$datafile;
CHECKPOINT_CHANGE#
           2302798
           2302798
           2302798
           2302798
           2302798
           2302798
           2302798
           2302798
8 rows selected.
SQL> select * from V$log;
    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARC STATUS
FIRST_CHANGE# FIRST_TIM
         1          1         68   52428800          1 NO CURRENT
      2302807 27-JUN-09
         2          1         66   52428800          1 YES INACTIVE
      2279864 26-JUN-09
         3          1         67   52428800          1 YES ACTIVE
      2300530 27-JUN-09
SQL> alter system checkpoint;
System altered.
SQL> select * from V$log;
    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARC STATUS
FIRST_CHANGE# FIRST_TIM
         1          1         68   52428800          1 NO CURRENT
      2302807 27-JUN-09
         2          1         66   52428800          1 YES INACTIVE
      2279864 26-JUN-09
         3          1         67   52428800          1 YES INACTIVE
      2300530 27-JUN-09
SQL> select checkpoint_change# from V$datafile;
CHECKPOINT_CHANGE#
           2302817
           2302817
           2302817
           2302817
           2302817
           2302817
           2302817
           2302817
8 rows selected.
SQL>What you see here, can you try to interpret it?
Alter checkpoint command merely pushes the writing and gets the checkpointing write complete. Its only the log switch which is going to do a complete checkpoint. Active means that the checkpointing for that group is started. The time perilod for which you see this status would depend on the size of the redo log file and also the contents that are there in it when it was switched. After checkpoining is complete for this group, the file be completely empty and would be marked as inactive.
HTH
Aman....

Force log switch using dbmcli

Hello!
How do I force a log switch using dbmcli?
For data protection purpose I would like to do this on daily basis.
The system has autolog=on, and I run the backups using dbmcli via crontab on a linux box. MaxDB version is 7.6.01.12
Regards,
Fredrik
Message was edited by:
Fredrik Rosengren
Message was edited by:
Fredrik Rosengren

Hi Fredrik,
with Oracle Databases you use logswitches to get online redo logs copied to archive logs even when these online redo logs are not yet completely filled.
Basically you just want to make sure to have the latest changes in your backup too.
Well in MaxDB there is no "switch logfile" because there is no such thing as the logfiles. And there is also no limitation like the one of Oracle when backing up log data.
If you want to backup each and all not yet backed up log entries: no problem!
Deactivate the automatic log backup, perform a manual log backup and restart the automatic logbackup.
The log segments in MaxDB are not like the online redo logfiles of oracle. They are just markers in the logarea that are used by the autolog features to know "oh, there had been some changes again - let's do a backup of that now".
You may also want to have a look into this note:
<a href="https://websmp206.sap-ag.de/~form/handler?_APP=01100107900000000342&_EVENT=REDIR&_NNUM=869267&_NLANG=E">#869267 - FAQ: MaxDB LOG area</a>
KR Lars

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Is there any way we can schedule Cluster Logs to be generated every time so that it would be easy for us to analyze the issue?
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Question about frequent log switches

I support an Oracle 10g database (10.2.0.4) and database activity has increase to the point that, during the heaviest parts of the day, log switches are occurring too frequently (15 - 20 times per hour!). We also utilize Data Guard to replicate the database to our DR site. We currently have 2 log groups with 2 membes in each group.
I understand that I can tackle this issue 2 ways: either to increase the size of my redo log files (they are currently at 50 Meg each), or I can add additional redo log groups to the database.
I would like to get some opinions on whether on solution is better than the other, or the pros and cons of each course of action.
Thank you in advance for your advice with my question!

CowTown_dba wrote:
Thanks for helping me to understand my true problem. The issue is that because of the frequent log switches, database performance is degrading.Maybe that's the cause, maybe it isn't.
Users are complaining about slow response. So if I add more groups it will buy the archiver extra time but it will not help with the slow response issue.Depends on the root cause of the slow response issue. That has yet to be determined. While it may be true that your car has a short in the electrical system and your car doesn't start, it doesn't necessarily follow that the car doesn't start because of the short in the electrical system.
>
I really appreciate everyone contributing to my understanding of the issue, and helping clarify the root problem so that I can fix it the first time around.
You guys rock!

Abnormally Log switches

Dear all,
In my oltp system,the redo size for per member is 20m,and the average log switch is in 10-15 mints.But today i saw a disturbing information in my alert_log......
Thread 1 advanced to log sequence 221335
Current log# 1 seq# 221335 mem# 0: O:\ORACLE\ORADATA\TEST\REDO_A\REDO01_A.LOG
Current log# 1 seq# 221335 mem# 1: O:\ORACLE\ORADATA\TEST\REDO_B\REDO01_B.LOG
Thread 1 advanced to log sequence 221336
Current log# 3 seq# 221336 mem# 0: O:\ORACLE\ORADATA\TEST\REDO_A\REDO03_A.LOG
Current log# 3 seq# 221336 mem# 1: O:\ORACLE\ORADATA\TEST\REDO_B\REDO03_B.LOG
Thread 1 advanced to log sequence 221337
Current log# 4 seq# 221337 mem# 0: O:\ORACLE\ORADATA\TEST\REDO_A\REDO04_A.LOG
Current log# 4 seq# 221337 mem# 1: O:\ORACLE\ORADATA\TEST\REDO_B\REDO04_B.LOG
Thread 1 advanced to log sequence 221338
Current log# 5 seq# 221338 mem# 0: O:\ORACLE\ORADATA\TEST\REDO_A\REDO05_A.LOG
Current log# 5 seq# 221338 mem# 1: O:\ORACLE\ORADATA\TEST\REDO_B\REDO05_B.LOG
Thread 1 cannot allocate new log, sequence 221339
All online logs needed archiving
Current log# 5 seq# 221338 mem# 0: O:\ORACLE\ORADATA\TEST\REDO_A\REDO05_A.LOG
Current log# 5 seq# 221338 mem# 1: O:\ORACLE\ORADATA\TEST\REDO_B\REDO05_B.LOG
What is the reason behind these 5 log switches at a time?I'm very much worried with this matter....
Any suggestion......................?????
Warm Regards,

Hi.
I guess you have a very high load values on your system... inserts / updates... Your database is running in archivlog mode. The archiver process could not backup the redo log files in that time period that the database take to round robin the log switches.
Its not a big deal you will gain a wait enqueue for database changes. You can increase the logfile size to avoid this problem. but keep in mind that in recovery case the recovery take more time.
*T

Redo log switching

11gR2
Found out log switched every a few mins (2, 3 mins) at peak periods. I will make the recommendation for larger redo logs such that switches will be every 20 to 30 mins .
Wanted to know what would be negative side of large redo logs?

>
11gR2
Found out log switched every a few mins (2, 3 mins) at peak periods. I will make the recommendation for larger redo logs such that switches will be every 20 to 30 mins .
Wanted to know what would be negative side of large redo logs?
>
Patience, grasshopper!
If it ain't broke, don't fix it. So first make sure it is broken, or about to break.
Unless you have an emergency on your hands you don't want to implement a change like that without careful examination of your current log file usage and history.
You need to provide more information such as typical size of your log files, number of log groups, number of members in each group, log archive policy, etc.
1. How often do these 'peak periods' occur? Do they occur fewer than 5 or 6 times a day? Or dozens of times?
2. How long do they last? A few minutes? Or a few hours?
3. What is the typical, non-peak rate of switches? This is really your base-line that you need to compare things to.
4. What has the switch pattern been over the last few weeks or months?
5. What has the growth in DB activity benn over the last few weeks or months? What do expect over the next few months?
6. What is your goal in reducing the frequency of log switches?
Basic negative sides include longer time to archive each log file (the fewer logs in each group the more impact here) and the length of time to recover in the event you need to. With large log files there is more for Oracle to wade through to find the relevant data for restoring the DB to a given point in time.
Your suggestion of every 20 - 30 minutes means 2 to 3 times per hour. If you currently switch 10 or 12 times per hour you are making a very big change.
Although you don't want to 'tweak' the logs unnecessarily you also don't want to make such large changes.
Everything in moderation. If your current switch rate is 10 or 12 times per hour you may want to first cut this to maybe 1/2 to 1/3: that is, to 4 or 5 time per hour. It all depends on the answers to questions like I ask above. If you post the answers to know if will be helpful to anyone trying to advise you.

Redo log switch frequency

Hi all experts,
I have a 10.2.0.4 database. I want to find out how often redo log switch is happening in the database. Is there a query on some sys/system view that could show me that?
Thanks,

Hi,
You can check bellow mention query which will give you idea of log switch completion in your database.
select to_char(first_time,'YYYY-MON-DD') day,
to_char(sum(decode(to_char(first_time,'HH24'),'00',1,0)),'99') "00",
to_char(sum(decode(to_char(first_time,'HH24'),'01',1,0)),'99') "01",
to_char(sum(decode(to_char(first_time,'HH24'),'02',1,0)),'99') "02",
to_char(sum(decode(to_char(first_time,'HH24'),'03',1,0)),'99') "03",
to_char(sum(decode(to_char(first_time,'HH24'),'04',1,0)),'99') "04",
to_char(sum(decode(to_char(first_time,'HH24'),'05',1,0)),'99') "05",
to_char(sum(decode(to_char(first_time,'HH24'),'06',1,0)),'99') "06",
to_char(sum(decode(to_char(first_time,'HH24'),'07',1,0)),'99') "07",
to_char(sum(decode(to_char(first_time,'HH24'),'08',1,0)),'99') "08",
to_char(sum(decode(to_char(first_time,'HH24'),'09',1,0)),'99') "09",
to_char(sum(decode(to_char(first_time,'HH24'),'10',1,0)),'99') "10",
to_char(sum(decode(to_char(first_time,'HH24'),'11',1,0)),'99') "11",
to_char(sum(decode(to_char(first_time,'HH24'),'12',1,0)),'99') "12",
to_char(sum(decode(to_char(first_time,'HH24'),'13',1,0)),'99') "13",
to_char(sum(decode(to_char(first_time,'HH24'),'14',1,0)),'99') "14",
to_char(sum(decode(to_char(first_time,'HH24'),'15',1,0)),'99') "15",
to_char(sum(decode(to_char(first_time,'HH24'),'16',1,0)),'99') "16",
to_char(sum(decode(to_char(first_time,'HH24'),'17',1,0)),'99') "17",
to_char(sum(decode(to_char(first_time,'HH24'),'18',1,0)),'99') "18",
to_char(sum(decode(to_char(first_time,'HH24'),'19',1,0)),'99') "19",
to_char(sum(decode(to_char(first_time,'HH24'),'20',1,0)),'99') "20",
to_char(sum(decode(to_char(first_time,'HH24'),'21',1,0)),'99') "21",
to_char(sum(decode(to_char(first_time,'HH24'),'22',1,0)),'99') "22",
to_char(sum(decode(to_char(first_time,'HH24'),'23',1,0)),'99') "23"
from v$log_history group by to_char(first_time,'YYYY-MON-DD');
Hope this might help you.
Thanks,
Vishal Joshi
Oracle Apps DBA

Dataguard- scheduling manual log switch to have minimal lag

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