How Cassandra handle blocking execute statement in datastax java driver

Question

Blocking execute fethod from com.datastax.driver.core.Session

public ResultSet execute(Statement statement);

Comment on this method:

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Answer 1

Besides the above answer,

Looks like execute() calls executeAsync(statement).getUninterruptibly(), so whether you manage your own "n thread pool" using execute() and block yourself until execution completes up to a max of n running threads OR using executeAsync() on all records, cassandra side performance should be roughly same, depending on execution time/count + timeouts.

They executions will all run connections borrowed from a pool, each execution has a streamId on client side and gets notified you via future when the response comes back for this streamId, limited by total requests per connection on client side and total requests limited by read threads on each node that was picked to execute your request, any higher number will be buffered in a queue (not blocked) limited by the connection maxQueueSize and maxRequestsPerConnection, any higher than this should fail. The beauty of this is that executeAsync() does not run on a new thread per request/execution.

So, there has to be a limit on how many requests can run via execute() or executeAsync(), in execute() you are avoiding beyond these limits.

Performance wise, you will start seeing a penalty beyond what each node can handle so execute() with a good size pool makes sense to me. Even better, use a reactive architecture to avoid creating so many threads that are doing nothing but waiting, so large number of threads will cause wasted context switching on client side. For smaller number of requests, executeAsync() will be better by avoiding thread pools.

DefaultResultSetFuture future = new DefaultResultSetFuture(..., makeRequestMessage(statement, null));
new RequestHandler(this, future, statement).sendRequest();