Learn more about computerscience with this collection
Understanding machine learning models
Improving data analysis and decision-making
How Google uses logic in machine learning
Phase 3: Python + Cassandra + Postgres (1)
Next they moved the pre-computed feeds into Cassandra and stored the full activity data in them to avoid having to query Postgres when loading the feed.
- To reduce memory usage and cost they stored the last 3,600 activities for active users, and only 180 for inactive users (falling back to Postgres after that point).
- To reduce compute costs they split fanout tasks in two: active users got a high priority queue, and inactive users a low priority one. The high priority queue had a higher capacity buffer to cope with spikes, whereas the low priority queue relied on autoscaling and spot instances.
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Phase 2: Python + Redis + Postgres
The next step was to pre-compute the feeds in Redis.
- They stored a feed for every user and populated them by fanning out new activities to all followers.
- To minimize memory usage they stored only activity IDs in Redis and queried Postgres wh...
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Phase 3: Python + Cassandra + Postgres (2)
Even though the performance of Cassandra was great, it was complex to optimize it and hard to diagnose it during slowdowns and other issues.
Also, after a point they often found themselves delegating logic to the database layer because it was hard to speed up the performance of Python.
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Phase 1: Python + Postgres
The first solution was to store all activities in a single Postgres table and build the feed at read-time with a query like:
SELECT * FROM love WHERE user_id IN (...)
This solution ran smoothly up to 10M rows and with some fine tuning it held...
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Phase 4: Go + RocksDB
In 2018 they upgraded their architecture again. They haven't disclosed how their data is organized, but they mentioned what technologies they are using.
They replaced Cassandra with Rock...
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The challenge of scaling activity feeds
Activity feeds show activities from the people you follow and they represent the core of many popular products such as Facebook, Twitter, Instagram, LinkedIn, and Pinterest.
Feeds are hard to scale because there is no clear way to shard the data across multiple machines. On...
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