I was curious to see how long it would take to load “index.html” from my web server, so I created http-ping.pl to measure the time it took to retrieve a webpage from my web server:
$ http-ping.pl -s prefetch.net -p 80 -d 2
Querying HTTP server prefetch.net:80 every 2 seconds (Ctrl-C to stop):
Mon Nov 29 18:00:21 2004: TCP Connection Time=0.034s HTTP GET Time=0.052s [Normal Delay]
Mon Nov 29 18:00:23 2004: TCP Connection Time=0.035s HTTP GET Time=0.052s [Normal Delay]
Mon Nov 29 18:00:25 2004: TCP Connection Time=0.035s HTTP GET Time=0.055s [Normal Delay]
Mon Nov 29 18:00:27 2004: TCP Connection Time=0.035s HTTP GET Time=0.053s [Normal Delay]
Mon Nov 29 18:00:30 2004: TCP Connection Time=0.035s HTTP GET Time=0.051s [Normal Delay]
This will display the time it takes to perform the TCP three way handshake ( Syn, Syn/Ack, Ack), and GET the index page from a web server. This was a quick and dirty hack, and a full rewrite in C (w/ SSL support and timings!) is forthcoming. If you are interested in using http-ping.pl, you can grab the code from prefetch.net.
I was debugging an I/O problem last week, and needed to see how an application was using a UFS file system on a Solaris 9 server. Solaris comes with the “truss” utility, which can be used to trace library and system calls. When truss is invoked with the “-t” option, only the system calls passed to “-t” will be traced:
$ truss -leaf -t open,close,write,lseek -p 7044
7044/1: psargs: /usr/local/bin/blah -ubpid 17595 -web -wtbhostname w4
7044/1: open("log/httpd_log", O_WRONLY) = 25
7044/1: lseek(25, 0, SEEK_END) = 0x04B33A05
7044/1: write(25, " SOME_ TEXT ".., 133) = 133
7044/1: close(25) = 0
This example is taken from an application I manage ( I didn’t write it ). The application opens a log file, seeks to the end of the file, writes 133-bytes of data, and then closes the log file. The application does this 100s of times per minute, which is extremely inefficient. To fix this problem, the applications needs to be modified to use a single open() and close(). This will also allow us to cluster writes (if the appropriate tunables and open() options are are set correctly) to the log file.
I was checking my openldap logfiles today, and noticed that the “cn” attribute wasn’t indexed. I found this by checking for the “index_param” string in my OpenLDAP logfiles:
$ grep "index_param failed" /var/log/openldap
Dec 25 13:37:19 winnie slapd[730]: [ID 635189 local4.debug] < = bdb_substring_candidates: (cn) index_param failed (18)
To fix this problem, I added an “index” statement to my slapd.conf:
index cn,mail,sn eq,pres,sub
Once the index was added, I rebuilt the indexes with the “slapdindex” utility:
$ slapindex -f /usr/local/openldap-common/etc/slapd.conf -b "dc=synackfin,dc=com"
The OpenLDAP documentation has more info in case your interested in learning more:
http://www.openldap.org/doc/admin22/
I have been trying to get a better grasp of some advanced bash concepts, and have been reading through the following reference manual. I am pretty familiar with C and perl arrays, but have never had a need to use arrays in a bash script. The syntax for a bash array is almost identical to Perl:
array[1]=12
echo ${array[1]}
This assigns the value 12 to the first slot in the array. Since bash variables are untyped, we can assign a string to the same array:
array[2]="my string"
echo ${array[2]}
This assigns the string “my string” to slot two in the array. Useful stuff!
I exchanged an email or two with Andy Tucker regarding Solaris 9 entropy pools, and found out that entropy statistics are available through mdb’s (modular debugger) “rnd_stats” dcmd:
$ uname -a
SunOS winnie 5.9 Generic_117171-14 sun4u sparc SUNW,Ultra-5_10
$ mdb -k
Loading modules: [ unix krtld genunix ip lofs nfs random ptm ]
> ::rnd_stats
Random number generator statistics:
8192 bits of entropy estimate
0 bytes generated for /dev/random
5998456 bytes generated for /dev/urandom
2277764 bits of entropy added to the pool
94006 bits of entropy extracted from the pool
4849216 bytes added to the random pool
240 bytes extracted from the random pool
With Solaris 10, you can use the “swrand_stats” and “rnd_stats” dcmds to get entropy statistics:
$ uname -a
SunOS sparky 5.10 s10_69 i86pc i386 i86pc
$ mdb -k
Loading modules: [ unix krtld genunix specfs dtrace ufs ip sctp uhci usba nca random lofs sppp nfs crypto ptm ]
> ::swrand_stats
Software-based Random number generator statistics:
8192 bits of entropy estimate
861095 bits of entropy added to the pool
8480 bits of entropy extracted from the pool
2318888 bytes added to the random pool
1060 bytes extracted from the random pool
> ::rnd_stats
Random number device statistics:
0 bytes generated for /dev/random
0 bytes read from /dev/random cache
36 bytes generated for /dev/urandom
I wish there was a way to tell if an application blocked because of a depleted pool in Solaris 9 ( dtrace may solve this problem in Solaris 10).