lance-format/lance

The ProjectionPlan::project_batch function is inefficient and noisy

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#5,069 opened on Oct 24, 2025

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good first issue

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Description

In take workloads we utilize a function called ProjectionPlan::project_batch. This function creates a OneShotExec that reads in the batch and a ProjectExec that applies the projection expressions. This is probably fine if there are actually projection expressions to evaluate. However, if we all we are doing is reordering or dropping columns (or especially if the projection is an identity projections 🤦) we are adding quite a bit of unneeded overhead.

To put this into context, in a recent random access benchmarking effort I found this to be responsible for about 8% of the latency even though there was no actual projection (it was just identity).

Contributor guide

Research direction
Profile the `ProjectionPlan::project batch` function to identify overhead, especially for identity or no op projections, then optimize by skipping unnecessary execution nodes.
Tech stack
rust
Domain
database
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
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Half day
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Active
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Clear
Prerequisites
RustDataFusion
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40