divison by zero errors on default Gentoo mysql

[Brian Fraser]

On a new gentoo box:
$ sudo emerge --sync
$ sudo emerge portage
$ sudo emerge -Du world
$ sudo emerge dev-perl/DBD-mysql
$ sudo emerge bzr
$ bzr branch lp:percona-toolkit
$ cd percona-toolkit/
$ PERCONA_TOOLKIT_BRANCH=`pwd` PERCONA_TOOLKIT_SANDBOX=/usr PATH=$PERCONA_TOOLKIT_SANDBOX/bin:$PATH LD_LIBRARY_PATH=$PERCONA_TOOLKIT_SANDBOX/lib prove t/pt-table-checksum/resume.t
t/pt-table-checksum/resume.t .. 30/48 09-14T06:59:25 Error checksumming table test.t3: Illegal division by zero at /home/vagrant/portable-test-suite/bin/pt-table-checksum line 8933.

This diff fixes it, although I haven't dug any further than that:
=== modified file 'bin/pt-table-checksum'
--- bin/pt-table-checksum 2012-08-29 23:00:34 +0000
+++ bin/pt-table-checksum 2012-09-14 04:45:08 +0000
@@ -8929,7 +8929,7 @@
             # Update the rate of rows per second for the entire server.
             # This is used for the initial chunk size of the next table.
             $total_rows += $cnt;
- $total_time += $tbl->{nibble_time};
+ $total_time += $tbl->{nibble_time} || 1;
             $total_rate = int($total_rows / $total_time);
             PTDEBUG && _d('Total avg rate:', $total_rate);

There's also a similar bug in pt-osc and this:
t/pt-archiver/issue_131.t ............ Illegal division by zero at /home/vagrant/portable-test-suite/bin/pt-archiver line 5784.

Which is $stat_total:
      foreach my $stat (
         reverse sort { $a->{time} <=> $b->{time} } values %summary )
      {
         my $pct = $stat->{time} / $stat_total * 100;
         printf($fmt, @{$stat}{qw(action count time)}, $pct);
         $total2 += $stat->{time};
      }

---

I've actually investigated a bit further. It may come down to this:
Ubuntu 12.04:
$ perl -MTime::HiRes=time -E '$t = time(); sleep 0.900; $t2 = time(); printf "%.6f\n%.6f\n", $t, $t2; printf "%.6f\n", ($t2 - $t)'
1347624407.872023
1347624407.872031
0.000008

Gentoo:
$ perl -MTime::HiRes=time -E '$t = time(); sleep 0.900; $t2 = time(); printf "%.6f\n%.6f\n", $t, $t2; printf "%.6f\n", ($t2 - $t)'
1347624428.420000
1347624428.420000
0.000000

Maybe Gentoo doesn't have a gettimeofday()? Or has it but with less precision than the spec describes? I don't know how to detect this from Perl, but I figure that defaulting to 0.009 should do the trick -- 1 second would throw the statistics out of the window, and looks like at least two microseconds are guaranteed.

[Brian Fraser (fraserbn)]

Fixed for pt-table-checksum in 2.1.8

[Daniel Nichter (daniel-nichter)]

I think we failed to mention this in the 2.1.8 Changelog, but that's ok.

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PT-581