The Start of a New Year and a Word on strace.

newyear

I want to take the opportunity in this blog post to wish everyone both a good holiday season, as well as New Year up ahead. This will likely be the last entry that I will be making before the start of 2014 and I hope that everyone can get some time to spend with their friends and loved ones.

Today I want to talk about strace. Many system administrators are aware of its usage but for those that aren’t familiar with it, an apt description from its Wikipedia page desribes it concisely below:

strace is a debugging utility for Linux and some other Unix-like systems to monitor the system calls used by a program and all the signals it receives, similar to “truss” utility in other Unix systems. This is made possible by a kernel feature known as ptrace.

I personally always find it useful when debugging hanging processes (commonly Apache, for example) but it can also be used for identifying questionable performance. One thing to keep in mind, however, is the overhead its usage incurrs. This can be demonstrated as follows:

Without strace:

time dd if=/dev/zero of=/dev/null bs=512k count=1024k
1048576+0 records in
1048576+0 records out
549755813888 bytes (550 GB) copied, 23.6136 s, 23.3 GB/s

real 0m23.615s
user 0m0.096s
sys 0m23.496s

With strace:

time strace -c dd if=/dev/zero of=/dev/null bs=512k count=1024k
1048576+0 records in
1048576+0 records out
549755813888 bytes (550 GB) copied, 82.8322 s, 6.6 GB/s

real 1m22.837s
user 0m5.757s
sys 1m24.015s

As one can see by the results, there is a significant performance penalty and this should always be taken into account when strace is used as a means to troubleshoot and examine system bottlenecks.

See you all next year!

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