Fix metrics-db segfault which might be related to parsing assignment*.gz files
Since May 6, 10:08 CEST, metrics-db's JVM sometimes segfaults with this output:
[java] Java Result: 134
[java] #
[java] # A fatal error has been detected by the Java Runtime Environment:
[java] #
[java] # SIGSEGV (0xb) at pc=0x00007febde77bdec, pid=6579, tid=140651047905024
[java] #
[java] # JRE version: 6.0_18-b18
[java] # Java VM: OpenJDK 64-Bit Server VM (14.0-b16 mixed mode linux-amd64 )
[java] # Derivative: IcedTea6 1.8.13
[java] # Distribution: Debian GNU/Linux 6.0.4 (squeeze), package 6b18-1.8.13-0+squeeze1
[java] # Problematic frame:
[java] # V [libjvm.so+0x3c3dec]
[java] #
[java] # An error report file with more information is saved as:
[java] # /srv/metrics.torproject.org/db/hs_err_pid6579.log
[java] #
[java] # If you would like to submit a bug report, please include
[java] # instructions how to reproduce the bug and visit:
[java] # http://icedtea.classpath.org/bugzilla
[java] #
A quick analysis shows that the segfault happens while processing .gz-compressed bridge pool assignment files. Attempts to reproduce this problem by reading the .gz file in question 100 times in a row and by setting up a separate metrics-db instance were not successful. Switched from commons-compress-1.0.jar to commons-compress-1.4.jar, even though the change log doesn't say anything about a possible segfault.