Re: directio and async io on redhat linux 3 and oracle 9i

chao_ping wrote:
> To Noons:
> I guess the create index on directio filesystem can be slower, is it
> true?

It can. Not in this case. About the same time. Of course, I tuned for directIO.

Here are the summary results I got:

RHAS3, Oracle 9.2.0.6 patched with 2448994, PIII 1GhzX4 cpu, NAS disk farm.

Conditions:

Create an index on a 120Mrow table, parallel 4, 8Kb blocks, DBFMR 8, dbwr_processes 4, same buffer cache sizes

Memory usage.

With O_DIRECT:
[nsouto_at_db2]$ free -mt

      total        used   free   shared   buffers   cached
Mem:  3010         978    2031   0        166       514
-/+ buffers/cache: 297    2712
Swap: 2047         0      2047
Total:5057         978    4079

Without O_DIRECT:
[nsouto_at_db2]$ free -mt

      total        used   free   shared   buffers   cached
Mem:  3010         2992   17     0        4         2697
-/+ buffers/cache: 291    2719
Swap: 2047         0      2047
Total:5057         2992   2064

Speeds:

With O_DIRECT:
Elapsed: 00:32:53.92

Without O_DIRECT:
Elapsed: 00:35:03.12

Conclusions:

Speed difference:	Essentially irrelevant: too small.
Memory usage:		Major difference in favour of O_DIRECT.