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TNS:could not resolve the connect identifier specified
Backtrace message unwound by exceptions
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end-of-file on communication channel
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invalid number
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resource busy and acquire with NOWAIT specified
error occurred at recursive SQL level string
ORACLE initialization or shutdown in progress
archiver error. Connect internal only, until freed
snapshot too old
unable to extend temp segment by string in tablespace
Credential retrieval failed
missing or invalid option
invalid username/password; logon denied
unable to create INITIAL extent for segment
out of process memory when trying to allocate string bytes
shared memory realm does not exist
cannot insert NULL
TNS:unable to connect to destination
remote database not found ora-02019
exception encountered: core dump
inconsistent datatypes
no data found
TNS:operation timed out
PL/SQL: could not find program
existing state of packages has been discarded
maximum number of processes exceeded
error signaled in parallel query server
ORACLE instance terminated. Disconnection forced
TNS:packet writer failure
see ORA-12699
missing right parenthesis
name is already used by an existing object
cannot identify/lock data file
invalid file operation
quoted string not properly terminated

Re: RE: increasing number of sessions vs. processes

Jesper Haure Norrevang

2005-01-19

Replies:
Paula,

Comments inline.

> There is a relationship between sessions on a database and the
> number of
> processes. What happens if we increase the number of sessions without
> increasing the number of processes???

The parameters SESSIONS and PROCESSES determine the
size of two arrays in the SGA.

If you try to create more sessions on an instance than specified
by the SESSIONS parameter, you will get an ORA-00018: maximum
number of sessions exceeded.

If you try to create more processes on an instances than specified
by the PROCESSES prameter, you wil get an ORA-00020: maximum
number of processes exceeded.

The number of sessions and processes on your instance can been
seen using a COUNT(*) against V$PROCESS and V$SESSION.
Your job is to determine resonable values, so your users can continue
to work without getting neither ORA-18 nor ORA-20 during normal
conditions. (A run away job, that keeps starting new sessions is not
a normal condition, and it should be stopped by ORA-18 or ORA-20
whichever happens first).

You can join the two V$-views using the columns V$SESSION.PADDR
and V$PROCESS.ADDR.

It is quite normal to see a 1:1 relationship between processes
and sessions. However one OCI-program can create multiple
sessions belonging to one process. Users of Oracle Portal
will experience this behaviour.

The default value for SESSIONS is 1.1*PROCESSES + 5.
It is appropriate for some databases and inappropriate for
others (e.g. Oracle Portal).

> Also, I remember a limit on the OS regarding the number of processes
> allowed per Oracle user - also I know there is a semaphore
> relationship.

On HP-UX there is a kernel parameter called NPROC. Like
PROCESSES and SESSIONS it should have a reasonable
value.


Hope this helps.

Regards
Jesper Haure Norrevang


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