Database performance degradation issue

Question

Hi,
We are having the database performance related problem.
Oracle database 8.1.7.0
when we use statement,
SQL> select name,value from v$sysstat where name ='redo buffer allocation retries';
NAME VALUE
redo buffer allocation retries 2540
Here, Redo retries value shown above is too big, which it should not be.
Currently we are having log_buffer = 65536 bytes (64 kb)
Is it necessary to increase the size of log_buffer ? does increasing the size of log_buffer will improve the database performance issue upto some extent ?
Also, regarding database buffer cache,
SQL> SELECT NAME, VALUE FROM V$SYSSTAT WHERE NAME IN ('db block gets', 'consistent gets', 'physical reads');
NAME VALUE
db block gets 4365099
consistent gets 1309280457
physical reads 103708616
From the above values, buffer cache hit ratio is 0.921052817
So, is it necessary to increase the size of database buffer cache ?
With Regards

Answer 1

Log_buffer 64k is likely too small. The default is 512k per CPU.
Increasing log buffer will decrease the number of redo allocation retries.
You need to set to 512K or 1M.
Buffer Cache Hit Ratio is a Meaningless Indicator of the Performance of the System, as Connor McDonald has demonstrated on http://www.oracledba.co.uk
You'd better strive to reduce I/O.
Also you will notice you need very big amounts of memory to get very little improvement.
Personally I would probably do something if BCHR was below 80 percent, but I know of situations where the problem is in the application and no value of db_blockf_buffers will be big enough.
Hth
Sybrand Bakker
Senior Oracle DBA