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

[Ben Wallach]

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

We just upgraded from 5.1 to 5.5. An insert script that used to take ~3 mins to insert ~200k rows into a MyISAM table with 3 indexes now takes ~8 mins! Removing the indexes solves the issue!?

Reads(selects) are fine (faster in 5.5 than 5.1)

Is something different about index behavior or could there be some oddball config parameter that may need to be tweaked?

Thanks in advance for any pointers!


System Info:
-----------
Fedora 17
Mysql 5.5.29-log
16GB RAM
MyISAM Key Buffer = 4GB
MyISAM index size = ~800 MB
MyISAM table size = 4.4 GB

INNODB Buffer Pool = 8GB
INNODB table+index size = ~12GB