Number of Open Files in DB Server

Question

Hi everyone,
I need some advise from Unix and Oracle experts on a query that my customer raised.
There are 3 additional application servers added recently. Before the app servers are brought up, I increased the Oracle processes and sessions parameters.
Then, my customer's UNIX administrator asked this question which made me ponder if it's true :
"Changing some of the Oracle parameters can also effect the Unix kernel parameters.  For example if there are 256 data files and 4 application servers each with 99 work processes that means that SAP can have at least 101,376 open files on the DB server without the additional Oracle open files and those need for the OS etc. "
I just wonder, does SAP processes really perform read-write on the Oracle datafiles ? Isn't it that the SAP processes logon to Oracle server processes, and it is the Oracle instance that perform the IO on the datafiles ?
The DB server has 343 processes which corresponds to the actual number of total processes in all the app servers. And there are 202 datafiles.
Does that means only 343 processes will open datafiles ? Or will it be 202 files open only ? Or is it like what the Unix administrator said in the example ?
Can someone please enlighten me ?
Thank you,
Kent Peh

Answer 1

Hi again
I give you some example with commands on a real system.
SQL> select count(*) from dba_data_files;
  COUNT(*)
       262
SQL> select count(*) from dba_temp_files;
  COUNT(*)
         8
SQL> show parameter processes
NAME                                 TYPE        VALUE
processes                            integer     620
So we have a system with 270 data/tempfiles and a maxium of 620 processes, so the theoretical maximum of open files can be over 270x620. Lets check how many processes we really have at the moment:
orasid> ps -ef | grep ora | wc -l
330
This includes, all shadow and background processes one shell (mine) and even my ps command )
But we do have slightly above 300 oracle processes here. So we might have roughly 270x300 = 81000 files open at the moment. Lets see, i use lsof to list the open files of the oracle command and redirect the output to a file, just because there is really a lot of files open on this system:
orasid> lsof -c oracle > /tmp/lsof.out
This includes directory entries, looks like there is some shared memory stuff, even tcp connections as well (we forgot about these until now). I think all these need file handles on unix as well, so be it. So in our example we have 46557 files open:
orasid> wc -l lsof.out
46557 lsof.out
You can dig further in the lsof.out, for example how many times is one single data file open:
orasid> grep /oracle/SID/sapdata2/stabd_4/stabd.data4 lsof.out | wc -l
209
I hope i did not do too many mistakes here, have fun!
Best regards, Michael
BTW: there is a maximum of 131072 (= 0x20000) open files on this system (HP-UX IA64)
orasid> /usr/sbin/kctune -v nfile
Tunable             nfile
Description         Maximum number of file descriptors (system-wide)
Module              fs
Current Value       0x20000
Edited by: mho on Feb 7, 2008 9:26 AM