Re: 5.1 to 5.5 upgrade causes significant write slowdown (MyISAM + indexes)

[Ben Wallach]

Thanks for all your feedback Scott.

At this point we are perplexed and are wondering if it's a hardware issue. I probably should have mentioned that we also upgraded OS version (from Fedora 11 to Fedora 17) and hardware/CPU (from Dell PowerEdge R200/Dual-core Pentium E2180/RAID-1 to DEll PowerEdge R210 II/Quad-Core Xeon E3-1220/RAID-1). I was reading that our new CPU (4-core) supprots Hyperthreading. Not sure what impact that has on MySQL.

Even though removing the indexes improves the performance, perhaps whatever extra work that happens when indexes are written puts the hardware (ala I/O) over the edge? Another observation is that when slave replication is turned back on (after being turned off during heavy writes on the master), it struggles real hard and long to catch up (lots of I/O and server very unresposive to other requests during..)

Next we may try installing MySQl 5.5 on the old hardware and see performance results. Try and narrow down the issue...