Cassandra data modeling blob - sql

Question

I am thinking of using cassandra for storing my data. I have a server_id, start_time, end_time, messages_blob.
CREATE TABLE messages (
server_id uuid,
start bigint,
end bigint,
messages_blob blob,
PRIMARY KEY ((server_id), start,end)
) WITH CLUSTERING ORDER BY (start,end);
I have two types of queries:
get all server_ids and messages_blob at start time > 100 and start time < 300.
get all messages_blob's for a bunch of server_ids at a time.
Can the above schema help me do it? I need to put billions of records in this table very quickly and do reads after all inserts have happened. The reads queries are not too many, compared to writes, but i need the data back as quickly as possible.

Answer 1

With this table structure you can only execute the 2nd query - you'll just need to execute queries for every single server_id separately, best via async API.
For 1st query, this table structure won't work, as Cassandra needs to know partition key (server_id) to perform query - otherwise it will require a full scan that will timeout when you have enough data in table.
To execute this query you have several choices.
Add another table that will have start as partition key, and there you can store primary keys of records in first table. Something like this:
create table lookup (start bigint, server_id uuid, end bigint,
primary key(start, server_id, end));
this will require that you write data into 2 tables, or you maybe can use materialized view for this task (although it could be problematic if you use OSS Cassandra, as it has plenty of bugs there). But you'll need to be careful with size of partition for that lookup table.
Use Spark for scanning the table - because you have start as first clustering column, then Spark will able to perform predicates pushdown, and filtering will happen inside Casasndra. But it will be much slowly than using lookup table.
Also, be very careful with blobs - Cassandra doesn't work well with big blobs, so if you have blobs with size more than 1Mb, you'll need to split them into multiple pieces, or (better) to store them on file system, or some other storage, like, S3, and keep in Cassandra only metadata.