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From: Colin Kuo <colinkuo.tw@gmail.com>
Date: Mon, 9 Jun 2014 18:53:41 +0800
Message-ID: 
 <CADEw-P7hc1W55BZdu1Y1CpWZJnEBZFJsnU7juPusmBukvdD9hg@mail.gmail.com>
Subject: Re: high pending compactions
To: user@cassandra.apache.org
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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.

Thanks,


On Sun, Jun 8, 2014 at 11:27 PM, S C <asf11@outlook.com> 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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<div dir=3D"ltr"><div>As Jake suggested, you could firstly increase &quot;c=
ompaction_throughput_mb_per_sec&quot; and &quot;concurrent_compactions&quot=
; 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 followin=
g compaction tasks. You could check the result of &quot;nodetool compaction=
stats&quot; and C* system log for double confirm.</div>

<div><br></div><div>If the running compaction is compacting wide row for a =
long time, you could try to tune &quot;in_memory_compaction_limit_in_mb&quo=
t; value.<br><div><br></div><div>Thanks,</div><div><div><br></div></div>

</div></div><div class=3D"gmail_extra"><br><br><div class=3D"gmail_quote">O=
n Sun, Jun 8, 2014 at 11:27 PM, S C <span dir=3D"ltr">&lt;<a href=3D"mailto=
:asf11@outlook.com" target=3D"_blank">asf11@outlook.com</a>&gt;</span> wrot=
e:<br>

<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">


<div><div dir=3D"ltr">I am using Cassandra 1.1 (sorry bit old) and I am see=
ing high pending compaction count.=C2=A0<span style=3D"font-size:12pt">&quo=
t;pending tasks: 67&quot; while active compaction tasks are not more than 5=
. I have a 24CPU machine. Shouldn&#39;t I be seeing more compactions? Is th=
is a pattern of high writes and compactions backing up? How can I improve t=
his? Here are my thoughts.</span><div>

<br></div><div><div><ol><li><span style=3D"font-size:12pt">Increase memtabl=
e_total_space_in_mb</span></li><li><span style=3D"font-size:12pt">Increase =
compaction_throughput_mb_per_sec</span></li><li><span style=3D"font-size:12=
pt">Increase concurrent_compactions</span></li>

</ol></div></div><div><br></div><div><span style=3D"font-size:12pt">Sorry i=
f this was discussed already. Any pointers is much appreciated.=C2=A0</span=
></div><div><br></div><div>Thanks,<div>Kumar</div></div> 		 	   		  </div><=
/div>


</blockquote></div><br></div>

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