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From Terje Marthinussen <tmarthinus...@gmail.com>
Subject memtablePostFlusher blocking writes?
Date Wed, 27 Apr 2011 16:01:21 GMT
0.8 trunk:

When playing back a fairly large chunk of hints, things basically locks up
under load.
The hints are never processed successfully. Lots of Mutations dropped.

One thing is that maybe the default 10k columns per send with 50ms delays is
a bit on the aggressive side (10k*20 =200.000 columns in a second?), the
other thing is that it seems like the whole memtable flushing locks up.

I tried to increase number of memtable flushers and queue a bit (8
concurrent flushers) to make things work, but no luck.

Pool Name                    Active   Pending      Completed
ReadStage                         0         0              1
RequestResponseStage              0         0        2236304
MutationStage                   100     17564        4011533
ReadRepairStage                   0         0              0
ReplicateOnWriteStage             0         0              0
GossipStage                       0         0           2281
AntiEntropyStage                  0         0              0
MigrationStage                    0         0              0
MemtablePostFlusher               1        13             50
StreamStage                       0         0              0
FlushWriter                       8        14             73
MiscStage                         0         0              0
FlushSorter                       0         0              0
InternalResponseStage             0         0              0
HintedHandoff                     1         8              3

A quick source code scan makes me believe that the MemtablePostFlusher
should not normally use a lot of time, but it seem like it does so here.
What may cause this?

Terje

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