question

Hello everybody,

I am new to Cassandra and I am trying to extract sketches (e.g. bloom filter) from some given data. While doing that, I came this far - my questions break down to the below:

CREATE TYPE bloomfilter_udt (
    n_as_sample_size int,
    m_as_number_of_buckets int,
    p_as_next_prime_above_m bigint,
    hash_for_string_coefficient_a list <bigint>,
    hash_for_number_coefficients_a list <bigint>,
    hash_for_number_coefficients_b list <bigint>,
    bloom_filter_as_map map<int, int>
);

CREATE OR REPLACE FUNCTION bloomfilter_udf (
    state bloomfilter_udt,
    value text,
    sample_size int
)
    CALLED ON NULL INPUT
    RETURNS bloomfilter_udt
    LANGUAGE java AS
        $$
        //fill state = bloomfilter_udt with some data
        return state;
        $$
    ;

CREATE OR REPLACE AGGREGATE bloomfilter_uda (
    text,
    int
)
    SFUNC bloomfilter_udf
    STYPE bloomfilter_udt
    INITCOND {};

1) When I call the aggregate, I would like to pass sample_size with a sub-query, e.g.

==> "SELECT bloomfilter_uda(name, (SELECT count(*) FROM test_table)) FROM test_table;" <==

Is that possible with Cassandra?

2) When I try to register the bloomfilter_uda, I get the following error:

==> InvalidRequest: Error from server: code=2200 [Invalid query] message="Invalid set literal for (dummy) of type bloomfilter_udt" <==

Can I just pass Cassandra data types as a state (map, list, set)?

3) If I assume, all of the above is my bad, how can I access the props of the state? Like

==> state.n_as_sample_size <==

Is this somehow possible?

I'd appreciate some help/hints.

Thanks

Andreas

[EDIT] For my minimum example, I follow these steps:

CREATE KEYSPACE my_keyspace
WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3};

CREATE TABLE my_table (
id timeuuid,
name text,
PRIMARY KEY(id, name)
);

INSERT INTO my_table (id, name) VALUES( now(), 'This is some random string');
INSERT INTO my_table (id, name) VALUES( now(), 'This is another random string');
INSERT INTO my_table (id, name) VALUES( now(), 'stringstringstring');
INSERT INTO my_table (id, name) VALUES( now(), 'test test test test');
INSERT INTO my_table (id, name) VALUES( now(), 'some final string');

CREATE OR REPLACE FUNCTION my_user_defined_function_triggered_on_each_row (state map<text,int>, value text, sample_size int)
CALLED ON NULL INPUT
RETURNS map<text,int>
LANGUAGE java
AS 
$$
//if sample size is not in result map, then put it
if(!state.containsKey("sample_size")) {state.put("sample_size", sample_size);};
//put the hashvalue (integer represented as a string) of each row as a key in result map and set the value to 1
String hashvalue = "" + value.hashCode();
if(!state.containsKey(hashvalue)) {state.put(hashvalue, 1);};
return state;
$$;

CREATE OR REPLACE AGGREGATE my_user_defined_aggregate_to_get_sketch (text, int)
SFUNC my_user_defined_function_triggered_on_each_row
STYPE map<text, int>
INITCOND {};

SELECT my_user_defined_aggregate_to_get_sketch(name, 5)
FROM my_table;

It work's until here and gives me the following output:

Now instead of storing everything in one map<text,int>, I would like to use a user defined data type, where I can put some more attributes with different data types. I follow there steps:

CREATE TYPE my_sketch(
sample_size int,
values map<text,int>
);

CREATE OR REPLACE FUNCTION my_user_defined_function_triggered_on_each_row_new(state my_sketch, value text, sample_size int)
CALLED ON NULL INPUT
RETURNS my_sketch
LANGUAGE java
AS 
$$
//For a minimal example let's do nothing and just return the state.
//I am guessing though, accessing my_sketch will be the next problem. I already tried something like state.my_size...
// I tried some versions like:
return state;
$$;

I test the new function calling on my_table. I expect the first parameter to be the return of each row. I call.

SELECT my_user_defined_function_triggered_on_each_row_new({"sample_size": 5, "values": {'value1': 5 }},  name, 5 )
FROM my_table ;

Gives me the expected output:

When i now try to wrap this up to a single return row with an aggregate, I implement my new aggregate like:

CREATE OR REPLACE AGGREGATE my_user_defined_aggregate_to_get_sketch_new (text, int)
SFUNC my_user_defined_function_triggered_on_each_row_new
STYPE my_sketch
INITCOND {}; 

But this gives me the error:

InvalidRequest: Error from server: code=2200 [Invalid query] message="Invalid set literal for (dummy) of type my_sketch"

I am using Cassandra 3.11.6 though.