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Linux-kernel 2.6.15 vs. 2.6.18

When we compared the results of the Dell PE 1950 in PostgreSQL 8.2-dev with the benchmarks from the previous review, we were initially pleasantly surprised with the difference. However, we soon became suspicious, because in theory it was virtually impossible for our new Dell machine to perform so much better than the Fujitsu which we tested before. We quickly formulated the hypothesis that the new version of the Linux kernel might play a role in the performance increase. Driver problems had forced us to run kernel 2.6.18 on the PowerEdge while the earlier tests had been done with version 2.6.15. To test the hypothesis, the RX300 was also upgraded to the new version, which turned to have a significant influence on the performance indeed. The development version of PostgreSQL 8.2 turned out to facilitate a performance increase of a good 19% with a load of 25 or more simultaneous users.

Database test Apollo 5 – effect of kernel version - PostgreSQL 8.2-dev

The picture for MySQL is completely different: with a single core switched on, fair gains can be recorded, but as soon as multiple threads must be handled, the gains turn into losses. Since it wasn't an option to test the Dell server running the old kernel, we decided to re-test the Fujitsu machine with the new kernel. This means that the remaining results in this article have all been obtained with version 2.6.18.

Database test Apollo 5 - effect kernel version - MySQL 4.1.20
Database test Apollo 5 - effect kernel version - MySQL 5.0.20a
Difference due to kernel versionMySQL 4.1.20MySQL 5.0.20aPostgreSQL 8.2-dev
1x single-core+6,2% up+2,9% up+20,2% up
2x single-core-2,7% up-4,4% up+20,2% up
1x dual-core-1,9% up-5,8% up+18,7% up
2x dualcore-1,6% up-5,7% up+16,0% up
Average0%-3,3% up+18,8% up