opensearch-project / opensearch-project/sql

[FEATURE][Enhancement][Calcite] Support batch friendly Limit operator

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calcite enhancement PPL
Dominant language
Java
Stars
176
Forks
229
Avg merge
2d 21h
Merged PRs (30d)
43

Description

Is your feature request related to a problem?
In Calcite, EnumerableLimit is implemented by using linq4j take.

  public static <TSource> Enumerable<TSource> take(Enumerable<TSource> source,
      final int count) {
    return takeWhile(
        source, (v1, v2) -> {
          // Count is 1-based
          return v2 < count;
        });
  }

However, the current implementation has to rely on the current row to decide whether the enumerator is able to move next, although it don't have to. For Limit, only the current row count is enough for predication.

Hence, it has downgrade when we have to fetch the next batch to provide the current row. And the downgrade will be amplified if there is a low-pass-rate filter operator after our scan operator, in which case we may have to fetch many batches even the whole index.

What solution would you like?
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What alternatives have you considered?
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Do you have any additional context?
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Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by tracing Calcite's EnumerableLimit implementation and the linq4j take method shown in the issue. Clarify how batch advancement should work without relying on the current row, then identify the relevant execution tests. Done means the Limit operator supports the requested batch-friendly behavior without the described extra batch fetches.

Written by the indexing model from the issue text.

Assessment

Tech stack
java
Domain
databases
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
25/100

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