Nested columns are not repartitioned: one chunk per batch instead of Rust's ~1 MB chunks

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
55/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
java
Domain
data

Research direction

Start with Repartitioner.supports and the byte sizing and head/tail slicing paths for StructData, ListData, and FixedSizeListData. Extend RepartitionInteropIntegrationTest with list<struct<utf8>> and struct columns, then compare chunk row counts and sizes with vortex-jni. Done means nested columns are repartitioned into comparable ~1 MB chunks.

Written by the indexing model from the issue text.

Description

bug

Repartitioner.supports covers Primitive, Bool, Decimal, Utf8 and Binary; struct, list, fixed-size-list, map and variant columns are written one chunk per input batch. Rust's RepartitionStrategy coalesces every column, nested ones included, into ~1 MB chunks of 8192-row multiples.

Found on Raincloud coig: conversations (list<struct<question: utf8, answer: utf8>>) is written as 3 chunks of 65536 rows (the Parquet import's batches), where Rust writes 22 chunks of 8192 rows. The column is 2.6% bigger than Rust's (63.74 MB vs 62.13 MB from vortex-jni 0.91), and a row-range or pruned read touches 8x more rows per chunk.

Fix: byte sizing and head/tail slicing for StructData, ListData and FixedSizeListData carriers, then admit them in supports.

Test first: extend RepartitionInteropIntegrationTest with list<struct<utf8>> and struct columns, comparing chunk row counts and sizes with vortex-jni.

Dominant language
Java
Stars
3
Forks
2
Avg merge
9h 19m
Merged PRs (30d)
154

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