In MySQL 5.5 we introduced a possibility to use alternative malloc implementations for MySQL. In Solaris we have found mtmalloc to be the optimal malloc implementation. For Linux we've previously found tcmalloc to be the optimal malloc implementation. However recently when working on a new MySQL feature I discovered a case where tcmalloc had a performance regression after running a very tough benchmark for about an hour. Actually I found a similar issue with the standard libc malloc implementation. So it seems that many malloc implementations gets into fragmentation issues when running for an extended period at very high load.
So I decided to contact Mark Callaghan to see if he had seen similar issues. He hadn't, but he pointed me towards an alternative malloc implementation which is jemalloc. It turns out that jemalloc is the malloc implementation used in FreeBSD among other things. I found a downloadable tarball of jemalloc, downloaded it and installed it on my benchmark computers. Given that MySQL already supports any generic malloc implementation it was a simple matter of pointing LD_PRELOAD towards jemalloc instead of towards tcmalloc to make this experiment.
The background is that tcmalloc gave about +5-10% better performance than libc malloc on Linux. Both libc malloc and tcmalloc have had performance regressions in certain situations. So the new results for jemalloc was very exciting. I got +15% compared to libc malloc and so far after using it for about a month I have found no performance regressions using jemalloc.