Database administration for fun and profit

Unix time from DB2

Here’s one way to obtain the Unix time value (the number of seconds since midnight on January 1, 1970) from a DB2 timestamp:

  (days(current_timestamp-current_timezone) - days('1970-01-01') )*86400 + 
  midnight_seconds(current_timestamp - current_timezone)

This can be used in a query directly or wrapped into a simple SQL user-defined function.

Top 5 SQL statements

Or may be top 10. Or 3. Whatever the number, we are often looking for the worst offenders kicking up the server’s CPU utilisation or I/O wait time to the skies. DB2 built-in snapshot functions are a great help. Run “select * from table (snapshot_dyn_sql('YOURDB', -1)) t order by rows_read desc fetch first 5 rows only” and you will get a list of the queries retrieving the most data. The only thing is, snapshot functions provide, well, snapshots of the DB2 monitor data and are not by themselves suitable for the collection of historical data. Monitor counters can be reset without your knowledge, for example when the database is deactivated or when the SQL statement expires from the package cache.

To ensure continuity of the data collected by snapshot functions we can quickly create a table where we will store historical snapshot information:

create table DYNSQLDATA as (select * from table (snapshot_dyn_sql('YOURDB', -1)) t) with no data

We will then insert output of the snapshot function into this table at regular intervals:

insert into DYNSQLDATA select t.* from table (snapshot_dyn_sql('YOURDB', -1)) t

Now we can easily determine which statements demand most resources and analyze their historical performance. Read More

Automatic monitoring of the SSL certificate expiration date

This is not really about database administration, but one of the problems I often face is monitoring of the expiration of SSL certificates on my clients’ web servers. It usually takes some time to renew a certificate, and it helps to know in advance that I need to get the process started.Here’s a little script that checks the certificate on a given web server and sends a reminder if it is about to expire:

#!/bin/bash# checks the ssl certificate expiration date of a given host
# Usage: ./checksslcert.sh <hostname> [<port>]
# Port defaults to 443 if not specified
test -z "$1" && echo "Usage: $0 <hostname> [<port>]" && exit 0
tempstr=$(openssl s_client -connect $1:${2:-443} 2>/dev/null >$0.log)
test $? -gt 0 && echo "Error accessing SSL certificate on $1" && exit 1
exptime=$(date -d"${tempstr#*=}" +"%s")
expdays=$(((${exptime} - $(date +"%s"))/84400))
echo "SSL certificate on $1 expires in $expdays days"
test $expdays -lt 45 && echo "Do something!" | mailx -s "SSL certificate on $1 expires in $expdays days" admin@domain.com

Run it daily by cron and you will never miss the expiration date again. The script needs the GNU date utility and openssl to be installed. It has been tested under bash, but you can easily modify it to run under other shells.

Downloading the logrotate script

I’ve been receiving comments recently from readers who have problems opening the logrotate archive. I did check (and re-check) the archive, and I’m absolutely positive that the URL is correct and the file is not corrupt and can be downloaded and opened. The only problem I can see is that when you use Internet Explorer (at least IE6 – did not try it with other version) to download the file, it gets renamed to “logrotatew.tar.tar” for some reason. Apparently, Explorer does not like the original “.tar.gz” extension.

If that happens to you make sure that you rename the downloaded file back to “logrotatew.tar.gz”; after that bsdtar, WinZip, gunzip, and other utilities will know how to deal with the file. As an example, here’s how to use bsdtar if you saved the file in c:\temp:

bsdtar -xvzf c:\temp\logrotatew.tar.gz

Poor man’s logrotate for Windows

Have you ever been bothered by the db2diag.log growing out of control? I have. While on Linux and Unix you have nice tools like logrotate and its analogs written in a number of script languages, no such luck if you run DB2 on Windows. There is no Windows port of logrotate, and your MSCE colleagues don’t always look favourably at you trying to install ActivePerl or Cygwin on a production server.

Having suffered enough from Notepad not being able to open a 300 megabyte db2diag.log, I have written a Windows command script to rotate the DB2 diagnostic log file. It uses only built-in Windows commands and therefore can run on any out of the box Windows 2000, Windows XP, or Windows 2003 system. By the way, it should work for any log files (with some limitations), not necessarily those generated by DB2.

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