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pg-log2amqp-cli

Purpose

  • Add knex-log messages onto an AMQP queue to be processed.

Installation

This module is installed via npm:

npm install pg-log2amqp-cli

Usage

DATABASE_URL=postgres://... \
  DATABASE_TABLE_NAME=logs \
  AMQP_URL=amqp://... \
  AMQP_SEARCH_QUEUE=logs \
  npm start

This will queue everything from the very beginning. If you only want later results you can also set an id offset with:

LOG_OFFSET=1337

Backpressure

Things to be aware of...

  • RabbitMQ has it's own backpressure. @see RabbitMQ Flow Control.
  • amqplib also implement a kind of writable stream like backpressure. @see amqplib Flow Control.
  • knex-log streams use pg-query-streams which does manage backpressure but there are 2 different configuration variables you might need to know about. highWaterMark is passed through to the underlying stream object to set it's backpressure value. batchSize however determines how many rows come back from postgres at a time (and how many get pushed onto the stream). This means that if the highWaterMark is low and the batchSize is high, the number of items in the queue will still be high.

How we use these things...

  • We currently create our knex-log streams with { batchSize: 16, highWaterMark: 16 } since log entries can be quite large (so we should only have up to 35 entries max waiting in the knex log readable queue (usually 16 from experience since it drains all before fetching more).
  • We pass that into an AmqpWritableStream which publishes to the queue. Each write returns the (mock write stream) results of sendToQueue() which will apply backpressure and stop writing if false. We also re-emit drain events from the AMQP channel to our stream to continue again once we are able to.
  • From the AMQP side we are just relying on their build in flow control which will restrict the incomming bandwidth, which should slow our write stream and knex log streams. I have done some basic testing locally and this does appear to be ok.

Contributing

Prerequisites

$ pip install pre-commit

Installation

$ pre-commit install --install-hooks

License

The BSD License

Copyright (c) 2018, Tim Allen

All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

  • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

  • Neither the name of the Tim Allen nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.