I understand that our problem might not(only|at all) be related to Perl, but since this is the language of choice and I know there is a lot of wisdom to be found here, I beg to ask...

When migrating several older Perl programs from an old to a new server we saw a dramatic decrease in execution speed, although the newer machine should be much faster.

Old machine:
Intel Celeron @2.2GHz, 4533 bogomips, 2GB RAM, Perl 5.10.1, Ubuntu 10.04 LTS, kernel 2.6.32-45, mysql 14.14 Distrib 5.1.66, SysV init

New machine:
Intel Core i3-4160 @3.6GHz, 7200 bogomips, 8GB RAM, Perl 5.20.2, Debian jessie, kernel 3.16.0-4, mysql 15.1 Distrib 10.0.23-MariaDB, systemd 215

The difference in one task was about 10-fold (i.e. the script took more than 10 times as long to run on the new machine, 0m58 vs. 11m). In another case the slow down was about 4 to 8-fold. Measurements were taken with the 'time' command on the command line.

The slowest program reads a dBase database table sequentially, mangles the data a bit and writes the records to a text and to a MariaDB SQL table. When commenting out the only $sth->execute statement the execution time jumps up from 11 minutes to 38 seconds. Some careful performance tuning on the MySQL/MariaDB server brought the execution time down to 2m40 (from 11m), still about 3 times slower than the old machine.

Another program, which does not use SQL, reads a dBase file, mangles the data a bit and writes them to a text file. Here the slowdown is about 4-fold. Some analysis with Devel::NYTProf found that most time is spent in IO::Handle which in turn is called by XBase.pm.

What I did and concluded so far:

• Moved the location of the dBase files which I read, from the server to the local machine, slight speed up of maybe 5%. So I conclude that the network is not the issue.
• Copied the same large numbers of small and large files from the server to the local machines. The new machine is about 3% faster, so I conclude that disk write IO is not the issue. I understand that this is a very crude and simple performance test, and real performance test takes much more. I at least cleared disk caches in advance of each test.
• Added the 'noatime' option to all affected file systems in /etc/fstab. No discernible speed up seen.
• Ran the two slowest programs with -d:NYTProf option.
  • the program which uses SQL spends 80% in DBI::st::execute, 17% in IO::Handle::CORE::read (which is called by XBase.pm);
  • the program which does not use the database spends about 87% of the time in IO::Handle::CORE::read (which is called by XBase.pm).
• Changed some parameters on the SQL server, which resulted in visible speedup of the programs using the SQL server. Nice, but not enough. Parameters changed were mostly buffer sizes.
• Compared the XBase.pm version, since a lot of time seems to be spent there.
  On the old machine it is 0.241, on the new one it is version 1.02. I did not yet look into the source of XBase.pm to see if there are any visible changes. Nor did I install the old version on the new machine. In fact I am a little bit afraid to do that and throw modules around... instead I came here to ask.

My question:
What else could be the reason for the slowdown? Is there anything which makes Perl 5.20 so much slower at IO handling? Is there anything obvious that I am missing, maybe something affecting IO in general? Buffering?

Any help is highly appreciated.

Thanks in advance,
Ekki

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