[fix][broker]Wrong backlog: expected 0 but got 1

[poorbarcode]

Motivation

• The backlog was calculated by managedLedger.entriesAddedCounter - cursor.messagesConsumedCounter

• When resetting a subscription, the broker resets the value cursor.messagesConsumedCounter this way: {new value} = {old value} - {how many positions the old value is larger than the new value}.

• The method managedLegder.getNumberOfEntries is used to calculate the number between two positions, but it has a bug, which will get a larger value than expected if the entry ID is a negative value.

• You can reproduce the issue by the new test

• [1] : https://github.com/apache/pulsar/blob/v4.0.7/managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerImpl.java#L3730C5-L3764C6

public long getNumberOfEntries(Range<Position> range) {
    long count = 0;
    // If the from & to are pointing to different ledgers, then we need to :
    // 1. Add the entries in the ledger pointed by toPosition
    count += toPosition.getEntryId(); // When the entry id is -1, it plush "-1" in mistake
    count += toIncluded ? 1 : 0;
    ...
    ...
    return count;
}

Modifications

• Fix the issue
• Improve the method position.comparate

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: x

[Copilot]

Pull Request Overview

This PR fixes an incorrect backlog calculation bug that occurs when resetting a subscription with negative entry IDs. The root cause was in the getNumberOfEntries method which didn't properly handle positions with negative entry IDs (e.g., -1), causing it to add a negative value to the count instead of treating it as 0.

• Fixed getNumberOfEntries() to handle negative toPosition entry IDs
• Added comparePositions() helper method to properly compare positions that may be invalid
• Added test to reproduce and verify the fix

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
ManagedLedgerImpl.java	Fixed getNumberOfEntries() to check if toPosition.getEntryId() < 0 before adding it to count
ManagedCursorImpl.java	Added comparePositions() helper method and updated internalResetCursor() to use it for proper position comparison
SimpleProducerConsumerTest.java	Added test case with two scenarios (with/without ledger trimming) to verify backlog calculation after subscription creation

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 81.81818% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.34%. Comparing base (678db6b) to head (00dc60a).
⚠️ Report is 69 commits behind head on master.

Files with missing lines	Patch %	Lines
...che/bookkeeper/mledger/impl/ManagedLedgerImpl.java	79.48%	3 Missing and 5 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #24938      +/-   ##
============================================
- Coverage     74.34%   74.34%   -0.01%     
- Complexity    33496    33700     +204     
============================================
  Files          1913     1920       +7     
  Lines        149315   150282     +967     
  Branches      17331    17444     +113     
============================================
+ Hits         111012   111725     +713     
- Misses        29475    29663     +188     
- Partials       8828     8894      +66     

Flag	Coverage Δ
inttests	26.31% <54.54%> (-0.79%)	⬇️
systests	22.85% <43.18%> (-0.17%)	⬇️
unittests	73.87% <81.81%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...che/bookkeeper/mledger/impl/ManagedCursorImpl.java	78.78% <100.00%> (+0.12%)	⬆️
...che/bookkeeper/mledger/impl/ManagedLedgerImpl.java	80.99% <79.48%> (-0.14%)	⬇️

... and 136 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.