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Benedict Elliott Smith commented on CASSANDRA-16663: ---------------------------------------------------- We should also look at propagating internode back-pressure to clients in 4.0. I wonder if that, combined with a client rate-limit, would be enough to deprecate the existing bytes-in-flight per client. Or at least we should look to see if we can rationalise them into a coherent system, with a unified API for configuration. It's already a lot of different limits. > 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 > Priority: Normal > Fix For: 4.0.x, 4.x > > > 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 queries are 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, we segment limits by operation type/keyspace/etc., 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. This is > obviously simplistic, and it does not account for the variation in cost > between individual queries, but even a fixed cost model should be useful in > aggregate. > * 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: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org