Hash function for getting key value

(3 posts) (2 voices)

• Started 4 months ago by rlebretonnic
• Latest reply from rlebretonnic
• This topic is not resolved

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1. 

   rlebretonnic
   Member

   Hi

   I look for something I didn'd find in doc.
   I created a column family and inserted some records using CLI.

   Now I request it using cqlsh. A technical column named KEY was added by cassandra. The value stored seems to be a hash value for the key used when creating the row within the CLI interface.

   I can request in cqlsh the column family using :
   

   select * from <CF> where key=<hash value of my rowkey>
   
   Is there a function for determining the hash value of the key and make a request like :

   select * from <CF> where key=hash(<rowkey>)

   Regards

   Posted 4 months ago #
2. 

   khahn
   Member

   Sorry you had trouble finding this info in the docs. Working with pre-CQL-3 applications on http://www.datastax.com/docs/1.2/ddl/legacy_table has some information, but it is sketchy.

   The column family you created using the CLI is a compact, legacy table (Thrift-compatible), not a CQL 3 table. CQL 3 uses more metadata than Thrift and the metadata won't be there when you try to access the legacy column family using CQL 3. The way CQL 3 deals with this is twofold: CQL3 picks a default name for the row key if none exists. For the row key, that default name is KEY. When you use CQL 3 to query legacy tables with no column names defined for data within a partition, CQL 3 generates the names (column1 and value1) for the data. Row key and cell names are encoded as byte arrays.

   Please see http://www.datastax.com/dev/blog/cql3-for-cassandra-experts and http://www.datastax.com/dev/blog/thrift-to-cql3 for all the details.

   There is no cqlsh function to do what you want to do.

   Posted 4 months ago #
3. 

   rlebretonnic
   Member

   OK... Thank for your answer.
   Basically it is a bad idea to mix Thrift and CQL :-)

   I also undestood that Cassandra's strategy is CQL according to the 1.2 documentation...

   Thank again. Regards.

   Posted 4 months ago #

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