[jira] [Created] (CASSANDRA-13553) Map C* Wide column to RocksDB key value data model

["Dikang Gu (JIRA)" <ji...@apache.org>]

Dikang Gu created CASSANDRA-13553:
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             Summary: Map C* Wide column to RocksDB key value data model
                 Key: CASSANDRA-13553
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13553
             Project: Cassandra
          Issue Type: Sub-task
          Components: Core
            Reporter: Dikang Gu
            Assignee: Dikang Gu


The goal for this ticket is to find a way to map Cassandra's wide column data model to RocksDB's key value data model.

To support most common C* queries on top of RocksDB, we plan to use this strategy, for each row in Cassandra:
1. Encode Cassandra partition key + clustering keys into RocksDB key.
2. Encode rest of Cassandra columns into RocksDB value.

With this approach, there are two major problems we need to solve:
1. After we encode C* keys into RocksDB key, we need to preserve the same sorting order in RocksDB byte comparator, as in original data type.
2. Support timestamp, ttl, and tombestone on the values.

To solve problem 1, we need to carefully design the encoding algorithm for each data type. Fortunately, there are some existing libraries we can play with, such as orderly (https://github.com/ndimiduk/orderly), which is used by HBase. Or flatbuffer (https://github.com/google/flatbuffers)

To solve problem 2, our plan is to encode C* timestamp, ttl, and tombestone together with the values, and then use RocksDB's merge operator/compaction filter to merge different version of data, and handle ttl/tombestones. 



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