Add Consistency Level for Schema Creation Operations
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Key: CASSANDRA-1335
URL: https://issues.apache.org/jira/browse/CASSANDRA-1335
Project: Cassandra
Issue Type: Improvement
Components: Core
Affects Versions: 0.7 beta 1
Environment: CentOS 5.2
Trunc
Reporter: Arya Goudarzi
Currently when applications create Keyspaces and CFs dynamically, user at
application level has to make 2-3 calls to Cassandra to verify consistency of
the schema as follows for example:
1. system_add_column_family
2. check_schema_agreement (will return a checksum of schema definitions and the
nodes agreeing on them, user has to count the result to see if there is one
checksum with all nodes meaning agreed or multiple checksums which means
disagreed;)
With clusters that have many application servers talking to them with high
concurrency, it is possible for result from check_schema_agreement to be
inconsistent in different nodes causing application misunderstanding of schema
since application is no aware how the schema checksum is calculated.
One solution that I've thought to add at the application level is to create
locks using memcache on CF and KS creation operations so that many clients
don't collide. However, I have to loop through check_schema_agreement and store
the state and also do describe_keyspace, hence a 3rd call, since I am not sure
how the checksum is calculated in order to verify I am not asking another
client to create the same CF or KS. This potentially could fall into infinit
loop if client calls fail and I have to bind to an application level timeout
detection to I don't loop forever.
I think it would highly make sense to have something like ConsistencyLevel
added to schema creation operation to avoid users having to implement their
locking and validation at their application level.
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