Writer: string columns written as per-chunk dicts where Rust uses its dict layout (up to 2x larger)

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難度
4/5
預估耗時
3-5 天
新手友好度
30/100
Issue 類型
缺陷
描述清晰度
基本清楚
活躍度
活躍
技術堆疊
java
領域
data

研究方向

Start with the globalDict option in WriteOptions and the admission probe that checks globalDictMaxRetainedBytes, then compare them with Rust's DictStrategy to see why these string columns are rejected. Reproduce with the bi-generico PrimeraLinea column and the clickbench-hits Title column, comparing the Java and Rust output trees. Done means these columns are written with the shared dict layout and the data bytes come close to the Rust sizes, with the admission reasoning explained in the write path.

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描述

perf

vortex-java's Parquet import vs the vortex-jni-written file, data bytes:

dataset column Rust Java Rust tree (most common) Java tree (most common)
bi-generico PrimeraLinea (Utf8?) 293.6 MB 585.8 MB (2.00x) 302x bitpacked + 198x fsst 1869x masked(dict(bitpacked, fsst(...)), constant)
bi-generico Concatenar 2 329.1 MB 395.9 MB (1.20x) 879x bitpacked + 279x onpair 3156x masked(dict(bitpacked, onpair(...)), constant)
bi-generico VER ANUNCIO, Concatenar 1, Producto ~290 / 290 / 212 MB 1.18–1.20x same shape same shape
clickbench-hits Title (Utf8) 1,101 MB 1,523 MB (1.38x) 2408x bitpacked + 1629x onpair 1335x dict(bitpacked, onpair(...))
clickbench-hits URL 1,933 MB 2,591 MB (1.34x) 4336x bitpacked + 2036x onpair 1852x onpair
clickbench-hits Referer 1,635 MB 1,836 MB (1.12x) 3243x bitpacked 1788x dict(bitpacked, onpair(...))

Rust's flats are mostly bare fastlanes.bitpacked codes: its dict layout shares one values pool across chunks. Java writes a per-chunk vortex.dict encoding (each chunk repeating its own values), and nullable ones under vortex.masked. ~+1.3 GB across these columns.

To narrow down: why Java's global dict layout (WriteOptions globalDict, default on) does not admit these columns — the admission probe / globalDictMaxRetainedBytes against Rust's DictStrategy.

主要語言
Java
星號
3
分支
2
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9 小時 47 分鐘
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