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Bulk skip in RunLengthBitPackingHybridDecoder / DictionaryValuesReader

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
72/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Active
Tech stack
java
Domain
data

Research direction

Start by reading RunLengthBitPackingHybridDecoder.readInt() and readNext(), then inspect skip(int) in DictionaryValuesReader and RunLengthBitPackingHybridValuesReader. Confirm how dictionary-encoded values are decoded and identify the relevant existing tests or test entry points. Done means bulk skipping uses the decoder path in all three readers while preserving the number of values skipped.

Written by the indexing model from the issue text.

Description

Type: enhancement
Motivation

Make Hive leverage bulk skip when implementing probe decode for Parquet, similarly to https://issues.apache.org/jira/browse/HIVE-22731, which was about ORC.

Problem

ValuesReader.skip(int n) ships with a naive default:

public void skip(int n) {
  for (int i = 0; i < n; i++) skip();
}

For dictionary-encoded columns (the common case), each skip() bottoms
out in RunLengthBitPackingHybridDecoder.readInt() — a mode switch,
array-index arithmetic, and a value the caller immediately discards.

Any filter-then-skip path (column-index row ranges, hash-join probe
filtering, runtime filters) pays this cost per skipped row.

Proposal
  1. Add RunLengthBitPackingHybridDecoder.skipInts(int n) — re-use
    readNext() per run, then advance currentCount by
    min(n, currentCount) instead of walking every value through
    readInt().
  2. Override skip(int) on DictionaryValuesReader and
    RunLengthBitPackingHybridValuesReader to call decoder.skipInts(n).
Component(s)

Core

Dominant language
Java
Stars
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Forks
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Avg merge
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Merged PRs (30d)
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