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From aaron morton <aa...@thelastpickle.com>
Subject Re: Help on MMap of SSTables
Date Tue, 04 Dec 2012 19:52:35 GMT
> Will MMapping data files be detrimental for reads, in this case?
No. 

> In general, when should we opt for MMap data files and what are the factors that need
special attention when enabling the same?
mmapping is the default, so I would say use it until you have a reason not to. 

mmapping will map the entire file, but pages of data are read into memory on demand and purged
when space is needed. 

Cheers

-----------------
Aaron Morton
Freelance Cassandra Developer
New Zealand

@aaronmorton
http://www.thelastpickle.com

On 4/12/2012, at 11:59 PM, Ravikumar Govindarajan <ravikumar.govindarajan@gmail.com>
wrote:

> Our current SSTable sizes are far greater than RAM. {150 Gigs of data, 32GB RAM}. Currently
we run with mlockall and mmap_index_only options and don't experience swapping at all.
> 
> We use wide rows and size-tiered-compaction, so a given key will definitely be spread
across multiple sstables. Will MMapping data files be detrimental for reads, in this case?
> 
> In general, when should we opt for MMap data files and what are the factors that need
special attention when enabling the same?
> 
> --
> Ravi


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