"fuser" is a great utility for Unix systems for determining who has a file opened or just if a file is opened by anyone. Related to Oracle maintenance, its handy when performing any kind of cleanup of tracefiles or audit files. Oracle dumps plenty of files under [a|b|u]dump yet as part of regular cleanup it's not wise to blindly remove these files. If a file is still open removing it doesn't release the space.
The problem is "fuser" can also be very slow. The point of the utility is to find all users
who have a given file open, but that literally means check every process on the
system to see if they have the associated file descriptor reserved, in DBA
terms "do a full scan" of all processes. On a system with thousands of processes and
thousands of files to check, the impact can be rather large.
The good news is Oracle is nice enough to frequently provide
the PID who owns a file within the filename itself. Since these audit and tracefiles are
exclusive to a PID this means you could grab the PID off the filename and check
one spot to see if that process still has the file open, instead of checking
all processes on the system.
As an example, the following shows an "fuser"
method and an lookup-by-PID method for checking all audit files to see if any
are open:
"fuser" Method
ls -1 $ORACLE_BASE/admin//adump/ora*.aud | while read AUD_FILE
do
[[ -n "`fuser $AUD_FILE | cut -d':' -f1`" ]] && echo
"File $AUD_FILE is open"
done
Lookup-by-PID Method
ls -1 $ORACLE_BASE/admin//adump/ora*.aud | while read AUD_FILE
do
AUD_FILE_BASE=`basename $AUD_FILE .aud`
AUD_FILE_PID=`echo $AUD_FILE_BASE | cut -d'_' -f2`
if [ `ls -l /proc/$AUD_FILE_PID/fd 2>/dev/null | grep -c
"$AUD_FILE"` -eq 1 ]; then
echo "File $AUD_FILE is open"
fi
done
The "Lookup" method takes a few extra lines of
code but the performance is dramatic. I
tested this on a system with 2500+ active processes with a few thousand audit
files, using "time" to compare the 2 methods.
For "fuser":
real 8m3.663s
user 0m11.197s
sys 0m50.258s
For "Lookup -by-PID"
real 0m0.951s
user 0m0.272s
sys 0m0.895s
Not every system has as many files to check so I ran both
tests against just 1 file, still with 2500+ active processes. The difference was still 1000x -
"fuser" = 0m3.144s, "Lookup-by-PID" = 0m0.003s.
For me the bottom line is that you can have a huge, positive
impact on performance if you're willing to add a smidge of intelligence to your
code.
