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From Chris Lohfink <clohf...@blackbirdit.com>
Subject Re: Question about MemoryMeter liveRatio
Date Tue, 26 Aug 2014 18:20:54 GMT
Computing how much actual memory the memtables cost including jvm overhead etc is expensive
(using https://github.com/jbellis/jamm).  So instead the memorymeter thread pool will periodically
find the size and compare it to the serialized size to compute the ratio to give an appropriate
estimate at real time.  This is used to determine how much memory a memtable is taking up
and how often to flush it.

---
Chris Lohfink

On Aug 26, 2014, at 12:20 PM, Leleu Eric <Eric.Leleu@worldline.com> wrote:

> Hi,
>  
>  
> I’m trying to understand what is the liveRatio and if I have to care about it.
> I found some reference on the web and if I understand them, the liveRatio represents
 the Memtable size divided by the amount of data serialized on the disk. Is it the truth?
>  
>  
> When I see the following log, what can I deduce about it ?
>  
>     INFO [MemoryMeter:1] 2014-08-26 19:02:41,047 Memtable.java (line 481) CFS(Keyspace='ufapi',
ColumnFamily='users') liveRatio is 8.52308554793235 (just-counted was 8.514143642185562).
 calculation took 3613ms for 272646 cells
>    INFO [MemoryMeter:1] 2014-08-26 18:36:09,965 Memtable.java (line 481) CFS(Keyspace='system',
ColumnFamily='compactions_in_progress') liveRatio is 40.1893491
> 1242604 (just-counted was 16.37869822485207).  calculation took 0ms for 7 cells
>  
>  
> According to my read, the liveRatio is set between 1 and 64. If My liveRatio is around
64, should I care about some things?
> Does Cassandra use the liveRatio for some internal task or it is just a metric?
>  
>  
> Regards,
> Eric
> 
> 
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