Confusion On Log_buffer Allocation

[twostep94]

Oracle 9.2.0.1 on AIX 5.3

Most of my databases are very small. When the databases were 8.1.7 on AIX 4.3.3, I had determined that 76K was the smallest value that would be allocated for the log_buffers (even if I set it lower, I got 76K) and therefore that is what I set most of the databases to.

Now that I have migrated to 9i on AIX 5.3, I notice that the log_buffer is actually showing 258K on these systems (via v$sgastat). Therefore, I assume that the 258K is now the minimum allocation for the new operating system.

I then started playing with the values. If I set the log_buffer parm to anything <= 128K, I get 258K. From that point on, whatever value I set the log_buffer to, I actually get a value much larger that whatever I specified - usually about 130K-140K larger (130K gives 261K, 160K gives 300K 250K gives 388K)).

Can anyone explain this?

Thanks,
Sheila

[tamilselvan]

Minimum log buffer size is platform dependent and also oracle release. It is quite natural you will see different values in different platforms.

Tamil

[twostep94]

I was not really surprised to see the minimum size increase when we went to the new operating system - I knew that this value was very dependent on the OS.

If I specify <= 128K, I get the apparent minimum of 256K (no problem here). What I am confused about is: If I specify anything > 128K, I actually get a value much larger (anywhere from 130K-140K larger).

Why would the *real* value be this much larger than the specified parm?

Sheila

[tamilselvan]

What is the value set for log_parallelism?

Tamil

[twostep94]

log_parallelism is defaulting to 1.

Sheila