Urgent Help - Redo Log problem

Question

Hi,
I have an implementation of Oracle 9i. Presently I have got 3 redo log groups with 2 members each. There are lot of updation and insertion of records going on with few tables. When the load increases the DB lands in a hang state and in the Log I get this message
Thread 1 cannot allocate new log, sequence 234
All online logs needed archiving
Current log# 1 seq# 233 mem# 0: D:\ORACLE\ORADATA\ORCL\REDO01.LOG
Current log# 1 seq# 233 mem# 1: D:\ORACLE\ORADATA\ORCL\REDO04.LOG
Can any one help me in solving this problem. I tried to Switch the log files but as they already are waiting for archiving so no use.
Any help on this will be highly helpfull to me as I am in Live environment.
Arvind

Answer 1

The way the log groups work is.
Log Writer(lgwr) starts writing to group 1. When group 1 fills up, it switches to group 2. When lgwr starts writing to group 2, the Archiver (arc) wakes up and starts writing group 1 to the archive file. When group 2 fills up lgwr start writing group 3 and arc archives group 2 once it has finished writing group 1. When group 3 fills up, lgwr starts writing to group 1 again, assuming that arc has finished writing group 1 to the archive.
In your case, it appears that arc is still writing group 1 when lgwr wants to use it again, so the database stalls until arc is finished writing group 1.
Fundamentally you have two choices. You can increase the size of each file in each log group, so they will fill up less often. However, this will also make arc take longer to archive the group. If you can gain enough time based on slower filling to offset the slower writing you should be ok.
The other option is to add a few more groups of the same size as the existing groups. This will give lgwr more groups to use before needing to start re-using earlier groups.
Typically, in our systems we run between 4 and 6 64M log groups and never see these hangs.
HTH
John