flow
Pravega
flow | Pravega | |
---|---|---|
2 | 2 | |
1,479 | 1,966 | |
0.5% | 0.1% | |
3.4 | 8.3 | |
10 months ago | about 1 month ago | |
Elixir | Java | |
Apache License 2.0 | Apache License 2.0 |
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flow
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Switching to Elixir
You can actually have "background jobs" in very different ways in Elixir.
> I want background work to live on different compute capacity than http requests, both because they have very different resources usage
In Elixir, because of the way the BEAM works (the unit of parallelism is much cheaper and consume a low amount of memory), "incoming http requests" and related "workers" are not as expensive (a lot less actually) compared to other stacks (for instance Ruby and Python), where it is quite critical to release "http workers" and not hold the connection (which is what lead to the creation of background job tools like Resque, DelayedJob, Sidekiq, Celery...).
This means that you can actually hold incoming HTTP connections a lot longer without troubles.
A consequence of this is that implementing "reverse proxies", or anything calling third party servers _right in the middle_ of your own HTTP call, is usually perfectly acceptable (something I've done more than a couple of times, the latest one powering the reverse proxy behind https://transport.data.gouv.fr - code available at https://github.com/etalab/transport-site/tree/master/apps/un...).
As a consequence, what would be a bad pattern in Python or Ruby (holding the incoming HTTP connection) is not a problem with Elixir.
> because I want to have state or queues in front of background work so there's a well-defined process for retry, error handling, and back-pressure.
Unless you deal with immediate stuff like reverse proxying or cheap "one off async tasks" (like recording a metric), there also are solutions to have more "stateful" background works in Elixir, too.
A popular background job queue is https://github.com/sorentwo/oban (roughly similar to Sidekiq at al), which uses Postgres.
It handles retries, errors etc.
But it's not the only solution, as you have other tools dedicated to processing, such as Broadway (https://github.com/dashbitco/broadway), which handles back-pressure, fault-tolerance, batching etc natively.
You also have more simple options, such as flow (https://github.com/dashbitco/flow), gen_stage (https://github.com/elixir-lang/gen_stage), Task.async_stream (https://hexdocs.pm/elixir/1.12/Task.html#async_stream/5) etc.
It allows to use the "right tool for the job" quite easily.
It is also interesting to note there is no need to "go evented" if you need to fetch data from multiple HTTP servers: it can happen in the exact same process (even: in a background task attached to your HTTP server), as done here https://transport.data.gouv.fr/explore (if you zoom you will see vehicle moving in realtime, and ~80 data sources are being polled every 10 seconds & broadcasted to the visitors via pubsub & websockets).
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An opinionated map of incremental and streaming systems (2018)
Elixir has a few interesting abstractions for that: GenStage, Flow, Broadway.
https://github.com/dashbitco/flow
Pravega
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Building a Real-Time Data Warehouse with TiDB and Pravega
Open sourced by Dell EMC, Pravega is a stream storage system and a Cloud Native Computing Foundation (CNCF) sandbox project. It is similar to Kafka and Apache Pulsar and provides stream and schema registry. But Pravega offers more functionalities:
- An opinionated map of incremental and streaming systems (2018)
What are some alternatives?
parallel_stream - A parallelized stream implementation for Elixir
kafka-streams-in-action - Source code for the Kafka Streams in Action Book
MapDiff - Calculates the difference between two (nested) maps, and returns a map representing the patch of changes.
Alluxio (formerly Tachyon) - Alluxio, data orchestration for analytics and machine learning in the cloud
fsm - Finite State Machine data structure
Seaweed File System - SeaweedFS is a fast distributed storage system for blobs, objects, files, and data lake, for billions of files! Blob store has O(1) disk seek, cloud tiering. Filer supports Cloud Drive, cross-DC active-active replication, Kubernetes, POSIX FUSE mount, S3 API, S3 Gateway, Hadoop, WebDAV, encryption, Erasure Coding. [Moved to: https://github.com/seaweedfs/seaweedfs]
graphmath - An Elixir library for performing 2D and 3D mathematics.
GlusterFS - Gluster Filesystem : Build your distributed storage in minutes
witchcraft - Monads and other dark magic for Elixir
Camlistore - Perkeep (née Camlistore) is your personal storage system for life: a way of storing, syncing, sharing, modelling and backing up content.
matrex - A blazing fast matrix library for Elixir/Erlang with C implementation using CBLAS.
Ceph - Ceph is a distributed object, block, and file storage platform