Plan an Cassandra implementation of the KeyValueStorage trait

[irach-ramos]

Examine the interface KeyValueStorage and figure out the exact Cassandra queries necessary for each function of the trait.

This is a preparation step before actually writing the implementation. Document the plan as a comment of this issue. Make sure to also plan the Cassandra statements required to initialize the database (create tables but only if does not exists, etc). The trait implementation will have to run these if needed so can be transparently used in place of the other implementations.

[irach-ramos]

KeyValueStorage in Cassandra

Table definition

Key value storage tables
CREATE TABLE kv_store (     namespace TEXT,     key TEXT,     value BLOB,     PRIMARY KEY (namespace, key) ); CREATE TABLE kv_sets (     namespace TEXT,     key TEXT,     value BLOB,     PRIMARY KEY ((namespace, key), value) ); CREATE TABLE kv_sorted_sets (     namespace TEXT,     key TEXT,     score DOUBLE,     value BLOB,     PRIMARY KEY ((namespace, key), score, value) );

Queries by function

trait function	statement
set	INSERT INTO kv_store (namespace, key, value) VALUES (?, ?, ?);
set_many	BEGIN BATCH     INSERT INTO kv_storage (namespace, key, value) VALUES ('NS', 'key1', 'value1');     INSERT INTO kv_storage (namespace, key, value) VALUES ('NS', 'key2', 'value2');     INSERT INTO kv_storage (namespace, key, value) VALUES ('NS', 'key3', 'value3'); APPLY BATCH;
set_if_not_exists	INSERT INTO kv_store (namespace, key, value) VALUES (?, ?, ?) IF NOT EXISTS;
get	SELECT value FROM kv_store WHERE namespace \= ? AND key \= ?;
get_many	SELECT key, value FROM kv_store WHERE namespace \= ? AND key IN (?, ?, ...);
del	DELETE FROM kv_store WHERE namespace \= ? AND key \= ?;
del_many	DELETE FROM kv_store WHERE namespace \= ? AND key IN (?, ?, ...);
exists	SELECT COUNT(*) FROM kv_store WHERE namespace \= ? AND key \= ?;
keys	SELECT key FROM kv_store WHERE namespace \= ?;
add_to_set	INSERT INTO kv_sets (namespace, key, value) VALUES (?, ?, ?);
remove_from_set	DELETE FROM kv_sets WHERE namespace \= ? AND key \= ? AND value \= ?;
members_of_set	SELECT value FROM kv_sets WHERE namespace \= ? AND key \= ?;
add_to_sorted_set	INSERT INTO kv_sorted_sets (namespace, key, score, value) VALUES (?, ?, ?, ?);
remove_from_sorted_set	DELETE FROM kv_sorted_sets WHERE namespace \= ? AND key \= ? AND value \= ?;
get_sorted_set	SELECT score, value FROM kv_sorted_sets WHERE namespace \= ? AND key \= ? ORDER BY score ASC;
query_sorted_set	SELECT score, value FROM kv_sorted_sets WHERE namespace \= ? AND key \= ? AND score >= ? AND score \<= ? ORDER BY score ASC;