Materialize candidates for whats-hot algo #1086
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devinivy
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May 24, 2023
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| await db.schema | ||
| .createView('algo_whats_hot_view') | ||
| .materialized() | ||
| .as(viewQb) | ||
| .execute() |
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Just wanted to flag this for you @dholms— this will lock post and post_agg for loading the initial data into the view. Future refreshes will be done concurrently which does not require locking.
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it's not possible to do the initial create concurrently is it?
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I tried to get that going by creating the view with no data, then running a concurrent refresh afterwards, but it doesn't work: apparently in order to perform a concurrent refresh the view already has to be populated.
dholms
reviewed
May 24, 2023
| .where('candidate.score', '<', maxScore) | ||
| .where('post.cid', '!=', cursorCid) | ||
| } | ||
| const keyset = new ScoreKeyset(ref('candidate.score'), ref('candidate.cid')) |
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good call switching this to a real keyset
dholms
reviewed
May 24, 2023
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| const { ref } = db.dynamic | ||
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| // materialized views are difficult to change, |
mloar
pushed a commit
to mloar/atproto
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Sep 26, 2023
* Setup whats-hot materialized view w/ params, run view maintainer in service entrypoint * Update whats-hot to use new materialized view, tidy * Update migration to create with no data * Revert whats-hot migration change for no data * Bump refresh rate for view down to 1min
mloar
pushed a commit
to mloar/atproto
that referenced
this pull request
Nov 15, 2023
* Setup whats-hot materialized view w/ params, run view maintainer in service entrypoint * Update whats-hot to use new materialized view, tidy * Update migration to create with no data * Revert whats-hot migration change for no data * Bump refresh rate for view down to 1min
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The whats-hot algo does some expensive work of paginating over a dynamic score for all post over the past day (i.e. the feed candidates).
This work replaces the subquery to score the candidates with a materialized view that is refreshed concurrently every two minutes (configurable). The materialized view is parameterized using a separate table so that we can alter the like threshold (default: 10) and the interval over which we grab candidates (default: 1day).
One complexity here is around how the refresh is scheduled. This piggy-backs off the
Leaderabstraction to ensure there's no more than one node maintaining the materialized view at a time. The creator of the view also needs to be the user who performs the refresh due to postgres limitations.