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From Viktor Jevdokimov <Viktor.Jevdoki...@adform.com>
Subject RE: What is the effect of reducing the thrift message sizes on GC
Date Tue, 18 Jun 2013 12:58:25 GMT
Our experience shows that write load (memtables) impacts ParNew GC most. More writes, more
frequent ParNew GC. Time of ParNew GC depends on how many writes was made during cycle between
ParNew GC's and size of NEW_HEAP (young gen).

Basicly ParNew GC itself takes longer when more objects have to be copied from young to old
space. So reads and compactions will not promote objects to old space (short living objects)
and you can see that increased reads and compactions during the same write load will increase
GC frequency but decrease GC pause time.

Best regards / Pagarbiai
Viktor Jevdokimov
Senior Developer

Email: Viktor.Jevdokimov@adform.com<mailto:Viktor.Jevdokimov@adform.com>
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From: Ananth Gundabattula [mailto:agundabattula@threatmetrix.com]
Sent: Tuesday, June 18, 2013 10:31 AM
To: user@cassandra.apache.org
Subject: What is the effect of reducing the thrift message sizes on GC

We are currently running on 1.1.10 and planning to migrate to a higher
version 1.2.4.

The question pertains to tweaking all the knobs to reduce GC related issues
( we have been fighting a lot of really bad GC issues on 1.1.10 and met with little
success all the way using 1.1.10)

Taking into consideration GC tuning is a black art, I was wondering if we
can have some good effect on the GC by tweaking the following settings:
*thrift_framed_transport_size_in_mb & thrift_max_message_length_in_mb*
*
*
Our system is a very short column (both in number of columns and data sizes
) tables but having millions/billions of rows in each column family. The typical
number of columns in each column family is 4. The typical lookup involves
specifying the row key and fetching one column most of the times. The
writes are also similar except for one keyspace where the number of columns
are 50 but very small data sizes per column.

Assuming we can tweak the config values :
*
*
* > thrift_framed_transport_size_in_mb & *
* >  thrift_max_message_length_in_mb *

to lower values in the above context, I was wondering if it helps in the GC
being invoked less if the thrift settings reflect our data model reads and writes ?

For example: What is the impact by reducing the above config values on the
GC to say 1 mb rather than say 15 or 16 ?

Thanks a lot for your inputs and thoughts.


Regards,
Ananth

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