astronomy-commons/lsdb

Specify memory required to merge computed worker results

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#678 opened on Apr 4, 2025

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enhancementhelp wanted

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Description

When creating a Dask Client we specify the number of workers and the memory limit for each of them. This means that each worker is assigned the same amount of memory. E.g.:

dask.distributed.Client(n_workers=16, memory_limit="4GiB")

When we hit compute one of those workers is responsible for merging the results of all individual computations and, if the result is bigger than that single worker's memory, the computation fails. We should be able to specify a different amount of memory required for a final worker to complete the computation.

There seems to be no way of specifying which merge worker to use on compute of a Dask DataFrame but that seems to be possible through the Client: https://distributed.dask.org/en/stable/api.html#distributed.Client.persist. Requires some investigation.

Contributor guide

Research direction
Investigate how lsdb's compute method configures Dask workers and merges results, and explore Dask's Client.persist API to find a way to specify a different memory limit for the final merge worker. Look at the code path from Client creation to compute, and identify where to add an optional parameter.
Tech stack
python
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
GitPythonDask
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50