swirl

High Performance Erlang Stream Processor

Requirements

• Erlang/OTP 25+

Environment variables

Examples

Starting a flow

ok = application:start(swirl),

FlowMod = swirl_flow_example,
FlowOpts = [
    {stream_names, [delivery]},
    {stream_filter, "exchange_id = 3 AND bidder_id IS NOT NULL"}
],
MapperNodes = [node()],
ReducerNode = node(),
{ok, Flow} = swirl_flow:start(FlowMod, FlowOpts, MapperNodes, ReducerNode),

StreamName = delivery,
Event = #{exchange_id => 1, bidder_id => 10},

swirl_stream:emit(StreamName, Event),

ok = swirl_flow:stop(Flow)

Implementing a flow

-module(swirl_flow_example).
-include_lib("swirl/include/swirl.hrl").

-behavior(swirl_flow).
-export([
    map/3,
    reduce/3,
    output/4
]).

%% swirl_flow callbacks
map(StreamName, Event, _MapperOpts) ->
    Type = ?L(type, Event),
    ExchangeId = ?L(exchange_id, Event),
    BidderId = ?L(bidder_id, Event),

    Key = {Type, StreamName, ExchangeId, BidderId},
    CounterIncrements = {1, 10},

    {Key, CounterIncrements}.

reduce(_Flow, Row, _ReducerOpts) ->
    Row.

output(_Flow, _Period, Rows, OutputOpts) ->
    %% do something with the output
    io:format("rows: ~p~n", [Rows]),

Stream Filter

exchange_id = 3 AND bidder_id IS NOT NULL
flight_id in (10, 12, 23) OR tag_id = 20
buyer_id notnull AND seller_id > 103

Swirl QL

variables:

atom()

values:

integer() | float() | binary()

boolean operators:

'and' | 'or'

comparison operators:

'<' | '<=' | '=' | '>=' | '>' | '<>'

inclusion operators:

in | notin

null operators:

null | notnull

Telemetry

swirl emits four telemetry events covering flow lifecycle and window dispatch. Attach handlers via telemetry:attach/4:

Window events fire per mapper / reducer flush — natural per-batch granularity, not per-event.

TODO

• node discovery
• boolean expression indexing

Tests

make test

License

The MIT License (MIT)

Copyright (c) 2013-2026 Louis-Philippe Gauthier

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.