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Version: 0.12

The bench Connector


This connector is not intended for production use, but for testing the Tremor runtime itself. To enable it pass --debug-connectors to tremor.

The bench connector enables controlled micro-benchmarking of tremor-based applications. Benchmarks and micro-benchmarking are an important part of the performance engineering practices of the tremor authors.

We maintain and publish benchmark results that are published every time code is commited to the main [tremor runtime](] git repository using bare metal infrastructure provided by the CNCF on Equinix Metal where we host a simple continuous benchmarking service designed for this purpose.


Config OptionDescriptionPossible ValuesRequired / OptionalDefault Value
sourceThe source file to read data from, can be xz compressedfile pathrequired
intervalThe interval between single events in nanoseconds. Set to 0 if you want events emitted as fast as possible.positive integeroptional0
chunk_sizeif provided, the source file data will be split into chunks of the given size, instead of split into lines.positive integeroptional
itersNumber of iterations through the whole source data to stop after. If not provided (and stop_after_secs is also not provided), the connector will iterate over the source data infinitely.positive integeroptional
base64If set to true, the source data will be base64 decoded.booleanoptionalfalse
is_transactionalIf set to true, events will be emitted as transactional (requiring ack/fail contraflow messages).booleanoptionalfalse
structuredIf set to true the benchmark report is output as JSON, if set to false it is printed in human-readable form.booleanoptionalfalse
stop_after_secsNumber of seconds after which the benchmark should be stopped.positive integeroptional
significant_figuresDigits of precision for latency HDR histogram results.positive integeroptional2
warmup_secsNumber of seconds to warm up. Events during this time are not accounted for in the latency measurements.positive integeroptional0


use std::time::nanos;
define connector bench from bench
codec = "json", # Decode each line as a JSON document
config = {
"source": "in.json", # Take the source data from `in.json` and turn each line into an event
"interval": nanos::from_millis(1), # Wait for 1ms between each event
"iters": 1, # Iterate only once through the data in `in.json`


The bench connector consists of two parts. The source part for generating synthetical loads of events and the sink part, measuring how many events it got and the latency of each event.

The source part will load an emulated source of events from a (possibly xz compressed) file and load them into memory. It is required to send the emitted events to the sink part via the in port of the same connector eventually. The pipelines and connectors in between can be considered the system that is subject to the benchmark.

The source part is replaying its contents for the duration of the test, or until the number of configured test iterations has been exceeded; whichever happens first. Once the test has been stopped a high dynamic range HDR Histogram is produced and printed to stdout. The histogram can be loaded into the web based histogram plotting tool for analysis.

Once the latency histogram and throughput measures have been emitted, the tremor runtime process is halted.

How do I write a benchmark?

The most important part of writing a benchmark with the bench connector is that the source part needs to be the source of events. Usually the source part emits events as fast as it possibly can, in order to see how much the whole system is actually able to handle inm the best case.

The sink part needs to receive the events eventually, otherwise the benchmark does not measure anything. In that case the bench connector can be used as a load generator.

A complete benchmark will define the bench connector as in the configuration example above with a system under test defined in a deployment file. A full example is provided for illustration.

define flow main
use tremor::connectors;

define connector bench from bench
codec = "json",
config = {
"source": "in.json",
"stop_after_secs": 10,
"warmup_secs": 2
create connector bench;

define pipeline bench_me
# this is just a dummy pipeline.
# What we actually benchmark here is how much throughput the vanilla tremor runtime
# without any application logic can achieve.
select event from in into out;
create pipeline bench_me;

# send synthetical load of events to the pipeline
connect /connector/bench to /pipeline/bench_me;
# send events to the bench connector for measuring and reporting
connect /pipeline/bench_me to /connector/bench;

deploy flow main;

This is a test of the benchmark connector itself that is exercised as part of our CI system, it can be run manually as follows:

$ git clone
$ cd tremor-runtime
$ cargo build --all --release # grab a coffee, this takes a while
$ cd tremor-cli/tests/integration/blaster # Piu piu!
$ export TREMOR_PATH=/path/to/tremor-runtime/tremor-script/lib
$ tremor test bench .
Running `target/debug/tremor test bench -v temp/bench`
Benchmark: Running bench
Tags: bench

| Value Percentile TotalCount 1/(1-Percentile)
| 8575 0.00000 1 1.00
| 15679 0.25000 249319 1.33
| 18559 0.50000 507133 2.00
| 20223 0.62500 626440 2.67
| 25087 0.75000 746698 4.00
| 237567 0.81250 808828 5.33
| 770047 0.87500 871282 8.00
| 1146879 0.90625 902347 10.67
| 1703935 0.93750 933194 16.00
| 2097151 0.95312 948800 21.33
| 2506751 0.96875 964503 32.00
| 2670591 0.97656 972719 42.67
| 2818047 0.98438 979971 64.00
| 2981887 0.98828 983951 85.33
| 3309567 0.99219 987641 128.00
| 3571711 0.99414 989559 170.67
| 3964927 0.99609 991540 256.00
| 4259839 0.99707 992494 341.33
| 4751359 0.99805 993481 512.00
| 5079039 0.99854 993936 682.67
| 5439487 0.99902 994468 1024.00
| 5537791 0.99927 994776 1365.33
| 5668863 0.99951 994894 2048.00
| 6029311 0.99963 995017 2730.67
| 6225919 0.99976 995133 4096.00
| 6619135 0.99982 995194 5461.33
| 6914047 0.99988 995349 8192.00
| 6914047 0.99991 995349 10922.67
| 6914047 0.99994 995349 16384.00
| 6914047 0.99995 995349 21845.33
| 6914047 0.99997 995349 32768.00
| 6946815 0.99998 995376 43690.67
| 6946815 1.00000 995376 inf
| #[Mean = 285758.86, StdDeviation = 701828.62]
| #[Max = 6946815, Total count = 995376]
| #[Buckets = 30, SubBuckets = 3968]
| Throughput (data): 0.5 MB/s
| Throughput (events): 99.5k events/s

Elapsed: 12s 40ms


It is an error to attempt to run a benchmark ( any deployment using the bench connector ) via the regular server execution command in the tremor command line interface

➜  blaster git:(main) ✗ tremor server run config.troy
tremor version: 0.12
tremor instance: tremor
rd_kafka version: 0x000002ff, 1.8.2
allocator: snmalloc
[2022-04-12T14:38:20Z ERROR tremor_runtime::system] Error starting deployment of flow main: Unknown connector type bench
Error: An error occurred while loading the file `config.troy`: Error deploying Flow main: Unknown connector type bench
[2022-04-12T14:38:20Z ERROR tremor::server] Error: An error occurred while loading the file `config.troy`: Error deploying Flow main: Unknown connector type bench
We are SHUTTING DOWN due to errors during initialization!
[2022-04-12T14:38:20Z ERROR tremor::server] We are SHUTTING DOWN due to errors during initialization!

In order to run the the tremor server run with the bench connector, add the --debug-connectors flag.