zlib performance improvements

In my blog entry on RHEL 6.4 I've mentioned that there have been performance enhancements for zlib compression. However I never got around to actually measure this until today.

I've taken the zlib test program called mingzip.c from the Red Hat zlib 1.2.3 and linked it dynamically against libz. Then I created a 2 GB data file by taring up /usr/share in the Red Hat file system three times. So it has quite some compressible text in it. Finally I ran five rounds of compression for this file on each RHEL 6.3 and RHEL 6.4 with default compression and "-9" maximum compression.

The result for the Red Hat update is a +13% throughput increase for the maximum compression and still a +8% throughput increase for normal compression.Your mileage may vary of course.

The same test comparing a SLES 11.2 with the new SLES 11.3 (which has an upgrade to zlib 1.2.7) shows a +25% throughput increase for the maximum compression and still a +13% throughput increase for normal compression.
This is a relative comparison: the reason the numbers are higher on SLES is that SLES 11.2 is significantly slower in this test than RHEL 6.3. The latest releases (6.4 and 11.3) are showing again about the same throughput.

Everyone using applications that dynamically link against zlib gets an improvement automatically. For applications who either ship their own version of zlib or statically link against it, the vendor needs to pick up the patch and put it into the next version for this improvement.