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From aaron morton <aa...@thelastpickle.com>
Subject Re: Memtables stored in which location
Date Thu, 21 Jul 2011 11:53:40 GMT
The data file with rows and columns, the bloom filter for the rows in the data file, the index
for rows in the data file and the statistics. 

Cheers

 
-----------------
Aaron Morton
Freelance Cassandra Developer
@aaronmorton
http://www.thelastpickle.com

On 21 Jul 2011, at 23:26, Nilabja Banerjee wrote:

> One more thing I want to ask here ...in the data folder of cassandra, for each columnfamily
four type of .db files are generated. for example:  CFname-f-1-Data.db, CFname-f-1-Filter.db,
CFname-f-1-Index.db, CFname-f-1-Statistic.db, 
> 
> What are these extensions are? 
> 
> Thank you
> 
> 
> 
> On 21 July 2011 16:11, samal <samal@wakya.in> wrote:
> 
> Any ways , some where memtable has to be stored right, like we say memtable data is flushed
to create sstable on disk.
> Exactly from which location or memory it will be getting from. is it like an objects
streams or like it is storing the values in commitlog.
> 
> A Memtable is Cassandra's in-memory representation of key/value pairs.
>  
> my next question is , data is written to commit log. all the data is available here,
and the sstable are getting created on disk, then where and when these memtables are coming
into picture
> 
> Commitlog is append only file which record write sequentially, more[2], can be thought
as check sum file, which to used to recalculate data for memtables in case of crash.
> A write first hits the CommitLog, then Cassandra stores/writes values to in-memory data
structures called Memtables. The Memtables are flushed to disk whenever one of the configurable
thresholds is met.[3] 
> For each column family there is corresponding memtable.
> There is generally one commitlog file for all CF.
> 
> SSTables are immutable once written to disk cannot be modified. It will only be replaced
by new SSTable after compaction
> 
> 
> [1]http://wiki.apache.org/cassandra/ArchitectureOverview
> [2]http://wiki.apache.org/cassandra/ArchitectureCommitLog
> [3]http://wiki.apache.org/cassandra/MemtableThresholds
> 
> 


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