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From aaron morton <>
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. 


Aaron Morton
Freelance Cassandra Developer

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

> One more thing I want to ask here 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 <> 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]
> [2]
> [3]

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