Caleb Rackliffe created CASSANDRA-16663:
-------------------------------------------
Summary: Request-Based Native Transport Rate-Limiting
Key: CASSANDRA-16663
URL: https://issues.apache.org/jira/browse/CASSANDRA-16663
Project: Cassandra
Issue Type: Improvement
Components: Messaging/Client
Reporter: Caleb Rackliffe
Assignee: Caleb Rackliffe
Together, CASSANDRA-14855, CASSANDRA-15013, and CASSANDRA-15519 added support
for a runtime-configurable, per-coordinator limit on the number of bytes
allocated for concurrent requests over the native protocol. It supports channel
back-pressure by default, and optionally supports throwing OverloadedException
if that is requested in the relevant connection’s STARTUP message.
This can be an effective tool to prevent the coordinator from running out of
memory, but it may not correspond to how expensive a query is or provide a
direct conceptual mapping to how users think about request capacity. I propose
adding the option of request-based (or perhaps more correctly message-based)
back-pressure, coexisting with (and reusing the logic that supports) the
current bytes-based back-pressure.
We can roll this forward in phases, where the server’s cost accounting becomes
more accurate, and the client/driver reacts more intelligently to (especially
non-back-pressure) overload, but something minimally viable could look like
this:
1.) Reuse most of the existing logic in Limits, et al. to support a simple
per-coordinator limit only on native transport requests in flight (i.e. where
requests have a fixed cost of 1). Under this limit will be CQL reads and
writes, but also auth requests, prepare requests, and batches.
* If the client specifies THROW_ON_OVERLOAD in its STARTUP message at
connection time, a breach of the per-node limit will result in an
OverloadedException being propagated to the client, and the server will discard
the request.
* If THROW_ON_OVERLOAD is not specified, the server will stop consuming
messages from the channel/socket, which should back-pressure the client, while
the message continues to be processed.
2.) This limit is infinite by default, and can be enabled via the YAML config
or JMX at runtime. (The literal default of -1 corresponding to “no limit” can
be used here.)
3.) The current value of the limit is available via JMX, and metrics around
coordinator operations/second are already available to compare against it.
4.) Any interaction with existing byte-based limits will intersect. (i.e. A
breach of any limit, bytes or request-based, will actuate back-pressure or
OverloadedExceptions.)
In this first pass, explicitly out of scope would be any work on the
client/driver side.
In terms of validation/testing, our biggest concern with anything that adds
overhead on a very hot path is performance. In particular, we want to fully
understand how the client and server perform along two axes constituting 4
scenarios. Those are a.) whether or not we are breaching the request limit and
b.) whether the server is throwing on overload at the behest of the client.
Having said that, query execution should dwarf the cost of limit accounting.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
