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Friday, 11 December 2009
By Steve Schnepp on Friday, 11 December 2009, 23:00 - c++
When writing portable cross-platform code, don't litter your code with preprocessor macros, use compile-time polymorphism instead.
A flexible build system will enable you to use advanced OOP-like compile-time polymorphism. That way you can hide all the specifics of the different platform behind an interface firewall. It is the usual way that most cross-platform toolkits and frameworks (such as QT, GTK or wxWidgets) are designed.
Thursday, 26 November 2009
By Steve Schnepp on Thursday, 26 November 2009, 22:00 - munin
I blogged about the munin monitoring system a while ago.
The fact the Munin team did quite a remarkable job in cleaning up the 1.2 code for the 1.4 release enabled me to add a native SSH transport for Munin, and made be able to get rid of all SSH tunnels.
Saturday, 14 November 2009
By Steve Schnepp on Saturday, 14 November 2009, 12:18 - sysadmin
I wanted to do some text replacement with a huge file (think ~18GiB), filled with huge lines (think ~2MiB per ligne)[1].
I naïvely piped it through sed and I was quite shocked that it
was CPU bound, and not I/O bound. The average rate was about 5 MiB/s (measured
with pv,
and the CPU was at almost 100%.The text file was gzipped on the filesystem, but
with a 1/100 ratio, so the gzip process just took less than 2% CPU. I replaced
then the sed -e with the Perl one-liner perl -lnpe,
and .... tadaa, it was flying at a rate of 50MiB/s !
While I'm a big fan of Perl, and know its effectiveness to handle text streams, I'm was still astonished : being 10x faster than sed was something.
But in the good old saying Too good to be true means suspect
, I
remembered something about the character encoding of the regular expression.
Since the system is entirely configured in UTF8, I suspected the
infamous UTF8 overhead over plain ASCII.
I was right : a little LANG=C in front of the sed command line
restored the rate to 50MiB/s.
So, beware of the performance impact of UTF8 strings, and try to avoid it if you can.
[1] For the record, it was a MySQL dump
Friday, 11 September 2009
By Steve Schnepp on Friday, 11 September 2009, 08:00 - sysadmin
NTP is very handy for server clock synchronisation, but it can be cumbersome to deploy.
Sometimes you just need to do a one-shot clock synchronisation, so you use
the standard date command. But there isn't a flag to easily copy a
setting to another.
Quite easy :
# date `ssh remoteuser@remotehost date +%m%d%H%M%Y.%S`
It's also very easy[1] :
# ssh root@remotehost date `date +%m%d%H%M%Y.%S`
[1] Yes, I do know that logging remotely as root is a security pitfall...
Tuesday, 8 September 2009
By Steve Schnepp on Tuesday, 8 September 2009, 22:00 - database
Doing a case insensitive search is a very common
task, but is quite hard to optimize correctly. But
since it's done via a UPPER(MY_COLUMN) = UPPER('MY_DATA'), it
doesn't use the index that could be on MY_COLUMN.
Different RDMS means different approaches.
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