Speed up fanout exchange (backport #14546) #14563
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* Add test case for binding args Khepri regression This commit adds a test case for a regression/bug that occurs in Khepri. ``` make -C deps/rabbit ct-bindings t=cluster:binding_args RABBITMQ_METADATA_STORE=mnesia ``` succeeds, but ``` make -C deps/rabbit ct-bindings t=cluster:binding_args RABBITMQ_METADATA_STORE=khepri ``` fails. The problem is that ETS table `rabbit_khepri_index_route` cannot differentiate between two bindings with different binding arguments, and therefore deletes entries too early, leading to wrong routing decisions. The solution to this bug is to include the binding arguments in the `rabbit_khepri_index_route` projection, similar to how the binding args are also included in the `rabbit_index_route` Mnesia table. This bug/regression is an edge case and exists if the source exchange type is `direct` or `fanout` and if different bindings arguments are used by client apps. Note that such binding arguments are entirely ignored when RabbitMQ performs routing decisions for the `direct` or `fanout` exchange. However, there might be client apps that use binding arguments to add some metadata to the binding, for example `app-id` or `user` or `purpose` and might use this metadata as a form of reference counting in deciding when to delete `auto-delete` exchanges or just for informational/operational purposes. * Fix regression with Khepri binding args Fix #14533 * Speed up fanout exchange Resolves #14531 ## What? Increase end-to-end message throughput for messages routed via the fanout exchange by ~42% (see benchmark below). In addition to the fanout exchange, a similar speed up is achieved for the following exchange types: * modulus hash * random * recent history This applies only if Khepri is enabled. ## How? Use an additional routing table (projection) whose table key is the source exchange. Looking up the destinations happens then by an ETS table key. Prior to this commit, CPUs were busy compiling the same match spec for every incoming message. ## Benchmark 1. Start RabbitMQ: ``` make run-broker RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS="+S 5" \ RABBITMQ_CONFIG_FILE="advanced.config" PLUGINS="rabbitmq_management" ``` where `advanced.config` contains: ``` [ {rabbitmq_management_agent, [ {disable_metrics_collector, true} ]} ]. ``` 2. Create a queue and binding: ``` deps/rabbitmq_management/bin/rabbitmqadmin declare queue queue_type=classic durable=true name=q1 && \ deps/rabbitmq_management/bin/rabbitmqadmin declare binding source=amq.fanout destination=q1 ``` 3. Create the load ``` java -jar target/perf-test.jar -p -e amq.fanout -u q1 -s 5 --autoack -z 60 ``` Before this commit: ``` sending rate avg: 97394 msg/s receiving rate avg: 97394 msg/s ``` After this commit: ``` sending rate avg: 138677 msg/s receiving rate avg: 138677 msg/s ``` The CPU flamegraph shows that `rabbit_exchange:route/3` consumes the following CPU amounts: * 13.5% before this commit * 3.4% after this commit ## Downsides Additional ETS memory usage for the new projection table. However, the new table does not store any binding entries for the following source exchange types: * direct * headers * topic * x-local-random * Add exchange binding tests Test that exchange bindings work correctly with the new projection tables `rabbit_khepri_route_by_source` and `rabbit_khepri_route_by_source_key`. * Always register all projections Khepri won’t modify a projection that is already registered (based on its name). * Protect ets:lookup_element/4 in try catch See #11667 (comment) for rationale. (cherry picked from commit a66c716)
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Resolves #14531
Resolves #14533
What?
Increase end-to-end message throughput for messages routed via the fanout exchange by ~42% (see benchmark below).
In addition to the fanout exchange, a similar speed up is achieved for the following exchange types:
This applies only if Khepri is enabled.
How?
Use an additional routing table (projection)
rabbit_khepri_route_by_sourcewhose table key is the source exchange.Looking up the destinations happens then by an ETS table key.
Prior to this commit, CPUs were busy compiling the same match spec for every incoming message.
For the bug fix of #14533, we also introduce a new projection called
rabbit_khepri_route_by_source_key. This can be thought of a v2 of the oldrabbit_khepri_index_routeprojection. The oldrabbit_khepri_index_routeprojection gets deleted in therabbitmq_4.2.0feature flag callback. The two new projections are registered at boot time (as discussed in #14543 (comment))Benchmark
where
advanced.configcontains:Before this commit:
After this commit:
The CPU flamegraph shows that
rabbit_exchange:route/3consumes the following CPU amounts:Downsides
Additional ETS memory usage for the new projection table.
However, the new table does not store any binding entries for the following
source exchange types:
Also, care must be taken to not add extensive amounts of bindings with the same source exchange to projection
rabbit_khepri_route_by_source. For fanout exchanges, binding an extensive amount of queues (e.g. thousands) to the same fanout exchanges is nonsensical anyway. One edge case could be binding thousands of queues to therandomexchange type. But even such an exotic use case could be realised efficiently by using intermediate random exchanges (i.e. exchange-to-exchange bindings) 🙂This is an automatic backport of pull request #14546 done by Mergify.