LMDB write performance on Linux

Quanah noted a few times in IRC that LMDB write performance was a lot slower after upgrading from Linux 2.6.x to 3.x. I've also observed some major slowdowns on an Ubuntu 3.5.0-23 kernel whenever the dirty page flusher is active. Apparently this is a known issue introduced in the 3.0 kernel series

http://lwn.net/Articles/486311/

I'm told that this has been fixed as of Linux 3.10. Unfortunately our most recent round of benchmarks has all been run on our 3.5.0-23 system. The SLAMD results we obtained for LMDB Modify throughput (tested back in February this year) are only about 60% of the speed we expected.

http://lkml.indiana.edu/hypermail/linux/kernel/1309.1/01585.html