Hi,
I already posted an answer for your question on
https://community.datastax.com/ but since you asked here as well:
1) When I call the aggregate, I would like to pass sample_size with a
> sub-query [..] Is that possible with Cassandra?
No.
2) When I try to register the bloomfilter_uda, I get the following error
> [...] Can I just pass Cassandra data types as a state (map, list, set)?
Yes, but you need to input a valid literal for your UDT by initializing at
least one field:
CREATE OR REPLACE AGGREGATE bloomfilter_uda ( text, int )
SFUNC bloomfilter_udf
STYPE bloomfilter_udt
INITCOND { n_as_sample_size : 0 };
This is a subtlety of the CQL parser; if you input just {} the parser would
be fooled into thinking that this is a set literal (an empty set) – hence
the (rather cryptic) error message.
3) If I assume, all of the above is my bad, how can I access the props of
> the state?
Inside functions and aggregates, if you need to access or modify a
user-defined type, you actually need to use the DataStax Java driver 3.x
API for User-defined types
<https://docs.datastax.com/en/developer/java-driver/3.9/manual/udts/>:
CREATE OR REPLACE FUNCTION bloomfilter_udf (
state bloomfilter_udt,
value text,
sample_size int
)
CALLED ON NULL INPUT
RETURNS bloomfilter_udt
LANGUAGE java AS
$$
state.setInt("n_as_sample_size", 42);
state.setInt("m_as_number_of_buckets" 42);
state.setLong("p_as_next_prime_above_m", 4242L);
List<Long> hashForStringCoefficients = ...;
state.setList("hash_for_string_coefficient_a",
hashForStringCoefficients, Long.class);
// etc.
return state;
$$
The variable state inside the Java block is of type UDTValue
<https://docs.datastax.com/en/drivers/java/3.9/com/datastax/driver/core/UDTValue.html>
.
Hope that helps.
Alex Dutra
On Thu, Apr 30, 2020 at 6:36 PM Andreas R. <andreasrimmelspac...@gmail.com>
wrote:
> Hello
>
> I am trying to extract sketches (e.g. bloom filter) from some given data.
> I came this far, questions 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
> $$
> //put n_as_sample_size in result
> //if(state.getUDTValue("n_as_sample_size") ==
> null){state.setInt("n_as_sample_size", sample_size);};
> //do some more stuff to the bloomfilter_udt
> return state;
> $$;
>
> CREATE OR REPLACE AGGREGATE bloomfilter_uda(text, int)
> SFUNC bloomfilter_udf
> STYPE bloomfilter_udt
> INITCOND {};
>
> 1) I would pass the 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 am kind of struggling with Cassandra and I'd appreciate some help.
>
> Thanks
> Andreas
>
> -- andreasrimmelspac...@gmail.com
>
>
