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Don Burleson Blog 







Thread 1 cannot allocate new log, sequence tips

Oracle Database Tips by Donald BurlesonJanuary 14, 2016

Question: I am getting the message "Thread 1 cannot allocate new log, sequence" in my alert log. 

Thu Jan 14 22:12:55 2016
Thread 1 cannot allocate new log, sequence 12345
Checkpoint not complete

What do I do to fix this problem?

Answer:  The "checkpoint not complete" messages are generated because the logs are switching so fast that the checkpoint associated with the log switch isn't complete.   

During that time, Oracle's LGWR process has filled up the other redo log groups and is now waiting for the first checkpoint to successfully execute.  Remember, Oracle will halt processing until the checkpoint completes successfully!  

Usually you see this "Thread 1 cannot allocate new log, sequence" error in your alert log:

Thu Jan 14 22:12:55 2016
Thread 1 cannot allocate new log, sequence 12345
Checkpoint not complete

Oracle has tips on avoiding the Thread 1 cannot allocate new log, sequence error, and

Oracle suggests that you might consider setting archive_lag_target to zero to reduce "Thread 1 cannot allocate new log, sequence" (log checkpoint not complete) messages:

alter system set archive_lag_target=0 scope=both;

Overall Oracle performance can be dramatically improved by increasing the log sizes so that logs switch at the recommended interval of 15 to 30 minutes (during peak DML processing times).  

Identify the current size of the redo log members from v$log.  Next, you record the number of log switches per hour and increase the size of the log to allow Oracle to switch at the recommended rate of under 6 log switches per hour.  

Also see my notes on how to monitor online redo log switches.  

For example, if the database redo log size is 1 megabyte and you are switching logs every 1 minute, you will need to increase the log size to 30 megabytes in size to allow it to switch every 30 minutes.  

For related details see "Manual Log Switching Causing "Thread 1 Cannot Allocate New Log" Message in the Alert Log" (MOSC ID 435887.1)

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