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From Colin Kuo <>
Subject Re: high pending compactions
Date Mon, 09 Jun 2014 10:53:41 GMT
As Jake suggested, you could firstly increase
"compaction_throughput_mb_per_sec" and "concurrent_compactions" to suitable
values if system resource is allowed. From my understanding, major
compaction will internally acquire lock before running compaction. In your
case, there might be a major compaction blocking the pending following
compaction tasks. You could check the result of "nodetool compactionstats"
and C* system log for double confirm.

If the running compaction is compacting wide row for a long time, you could
try to tune "in_memory_compaction_limit_in_mb" value.


On Sun, Jun 8, 2014 at 11:27 PM, S C <> wrote:

> I am using Cassandra 1.1 (sorry bit old) and I am seeing high pending
> compaction count. "pending tasks: 67" while active compaction tasks are
> not more than 5. I have a 24CPU machine. Shouldn't I be seeing more
> compactions? Is this a pattern of high writes and compactions backing up?
> How can I improve this? Here are my thoughts.
>    1. Increase memtable_total_space_in_mb
>    2. Increase compaction_throughput_mb_per_sec
>    3. Increase concurrent_compactions
> Sorry if this was discussed already. Any pointers is much appreciated.
> Thanks,
> Kumar

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