quickwit-oss/tantivy

Optimize Segment Readers Alive Doc Iterator

Open

#296 opened on May 8, 2018

View on GitHub
 (3 comments) (0 reactions) (0 assignees)Rust (499 forks)batch import
enhancementgood first issueperformance

Repository metrics

Stars
 (8,354 stars)
PR merge metrics
 (Avg merge 12d 14h) (20 merged PRs in 30d)

Description

Noted in PR #293

Use the same trick as what is used in the [BitSetDocSet] (https://github.com/tantivy-search/tantivy/blob/78673172d001a0c4c7c73cdd3d9923fc43fc0312/src/query/bitset/mod.rs) which relies on TinySet

In a nutshell : instead of looping on the bitset to find the next thing alive, it uses a special cpu instruction to get the next bit set to 1 in a u64. The instruction is not free, but except if your bitset is EXTREMELY saturated it is generally faster.

https://github.com/tantivy-search/tantivy/pull/293#discussion-diff-186488306R373

Contributor guide

Research direction
Study the BitSetDocSet implementation in tantivy's query/bitset/mod.rs linked in the issue. Understand how the TinySet trick uses a CPU instruction to find the next set bit in a u64. Then locate the Segment Readers Alive Doc Iterator code path and refactor it to use the same optimization. Benchmark to ensure performance improvement.
Tech stack
rust
Domain
backendperformance
Issue type
Performance
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.
1-2 days
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.
Clear
Prerequisites
RustBit manipulation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40