jasonz-lanceandClaude Opus 5 e907ff8c0e perf(python): drop O(max_shuffle_distance) prefetch scan in 2-phase reads
The background prefetch added in ecf44fed topped up its queue by walking
raw plan positions ahead of the read watermark, bounded by
`2 * max_shuffle_distance`, until it had found `prefetch_depth` distinct
blocks not already loaded or in flight.

That bound is a count of *ranks*, not of blocks, so with the default
`max_shuffle_distance` of 16384 the scan window covers 32768 ranks but
only ~8 distinct blocks -- fewer than the prefetch depth of 16. The loop
could therefore never satisfy its exit condition and ran all 32768
iterations, each one a Python-level scalar extraction out of a numpy
array, on *every* `__getitems__` call. Prefetching upcoming blocks
regressed 2-phase read throughput by ~5.6x (107 -> 19 MB/s on a local
NVMe benchmark).

Precompute the distinct blocks in first-needed order once, in __init__,
and have prefetch walk that instead: one step per block rather than one
per rank, so the scan is bounded by the block count (~24 here) and exits
as soon as the queue is full. Blocks whose last plan position is already
behind the watermark are skipped -- they can never be needed again.

Restores local-NVMe 2-phase read throughput to 78.7 MB/s.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
2026-10-08 16:35:24 -07:00
2023-03-17 18:15:19 -07:00
2025-03-10 09:01:23 -07:00

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LanceDB

The Multimodal AI Lakehouse

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The ultimate multimodal data platform for AI/ML applications.

LanceDB is designed for fast, scalable, and production-ready vector search. It is built on top of the Lance columnar format. You can store, index, and search over petabytes of multimodal data and vectors with ease. LanceDB is a central location where developers can build, train and analyze their AI workloads.


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Key Features:

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Python SDK https://lancedb.github.io/lancedb/python/python/
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