01-21-2011
Performance problem - waiting on cache
My server is running HP-UX 11.23 and one Oracle database. The server has 8 CPUs and is mostly idle all the time. Buffer cache is set to 10%min/max with 5GB memory on the server.
I have a user complaining that a batch process is all of a sudden taking a long time to finish. The DBA gave me the PID of the offending query and when I look up that process in Glance it shows the reason for waiting is CACHE. I set the update interval to 1 second and it never changes from cache. The process is consuming little CPU but still waits on cache.
Eventually the process will finish and die but it takes much, much longer than it used to just a few days ago. I know of no other processes that exhibit this behavior yet everyday this one process does the same thing, even with a new PID.
My hypothesis is that the server thinks that some data resides in cache but does not so it waits and waits. This doesn't really make sense to me but I cannot think of anything else that might cause this.
I have tried scouring the net for answers and have found none. If someone has any kind of logical guess of what might cause this behavior I'd love to hear it. It might help me figure out what is really going on.
Thanks,
Kevin
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KCM(8) BSD System Manager's Manual KCM(8)
NAME
kcm -- process-based credential cache for Kerberos tickets.
SYNOPSIS
kcm [--cache-name=cachename] [-c file | --config-file=file] [-g group | --group=group] [--max-request=size] [--disallow-getting-krbtgt]
[--detach] [-h | --help] [-k principal | --system-principal=principal] [-l time | --lifetime=time] [-m mode | --mode=mode]
[-n | --no-name-constraints] [-r time | --renewable-life=time] [-s path | --socket-path=path] [--door-path=path] [-S principal |
--server=principal] [-t keytab | --keytab=keytab] [-u user | --user=user] [-v | --version]
DESCRIPTION
kcm is a process based credential cache. To use it, set the KRB5CCNAME enviroment variable to 'KCM:uid' or add the stanza
[libdefaults]
default_cc_name = KCM:%{uid}
to the /etc/krb5.conf configuration file and make sure kcm is started in the system startup files.
The kcm daemon can hold the credentials for all users in the system. Access control is done with Unix-like permissions. The daemon checks
the access on all operations based on the uid and gid of the user. The tickets are renewed as long as is permitted by the KDC's policy.
The kcm daemon can also keep a SYSTEM credential that server processes can use to access services. One example of usage might be an nss_ldap
module that quickly needs to get credentials and doesn't want to renew the ticket itself.
Supported options:
--cache-name=cachename
system cache name
-c file, --config-file=file
location of config file
-g group, --group=group
system cache group
--max-request=size
max size for a kcm-request
--disallow-getting-krbtgt
disallow extracting any krbtgt from the kcm daemon.
--detach
detach from console
-h, --help
-k principal, --system-principal=principal
system principal name
-l time, --lifetime=time
lifetime of system tickets
-m mode, --mode=mode
octal mode of system cache
-n, --no-name-constraints
disable credentials cache name constraints
-r time, --renewable-life=time
renewable lifetime of system tickets
-s path, --socket-path=path
path to kcm domain socket
--door-path=path
path to kcm door socket
-S principal, --server=principal
server to get system ticket for
-t keytab, --keytab=keytab
system keytab name
-u user, --user=user
system cache owner
-v, --version
Heimdal May 29, 2005 Heimdal