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From Todd Burruss <bburr...@real.com>
Subject memory question
Date Mon, 22 Mar 2010 22:14:09 GMT
after running my cluster for a while performance has become unacceptable, 200+ ms for reads.
 if running well, i see reads <10ms.  when i run iostat the disk is being hammered by reads.
 seems like i/o caching isn't even being used

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           2.81    0.00    1.41   13.62    0.00   82.16
Device:         rrqm/s   wrqm/s   r/s   w/s    rMB/s    wMB/s avgrq-sz avgqu-sz   await  svctm
 %util
cciss/c0d0p1
               0.00     0.00  0.00  0.00     0.00     0.00     0.00     0.00    0.00   0.00
  0.00
cciss/c0d1p1
               0.00     0.00 848.50  0.00    13.66     0.00    32.98    21.50   25.23   1.18
100.05

i run top and i see cassandra's memory usage as follows:

  PID USER     PR NI VIRT  RES SHR S %CPU %MEM    TIME+ COMMAND
31510 bburruss 19  0 359g  37g 27g S 48.8 80.1  2137:30 java


i set -Xmx10g so it isn't java using the memory.  is it mmap i/o?  what would be causing the
huge memory usage?  it seems reasonable that the performance is bad because the i/o cache
can't be used properly.


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