consumer: fix EventsGroup memory retention

[wlwilliamx]

What problem does this PR solve?

Issue Number: close #4056

What is changed and how it works?

• Introduce EventsGroup.ResolveInto to copy out resolved events and clear the resolved prefix pointers before reslicing, avoiding Go GC retention of already-flushed DMLEvents.
• Switch kafka-consumer / pulsar-consumer to use ResolveInto when flushing by watermark or before executing DDL.
• Downgrade several high-frequency per-event logs from INFO/WARN to DEBUG to reduce log flooding under heavy workloads.
• Add unit tests for ResolveInto to ensure correctness and prevent pointer-retention regressions.

Check List

Tests

• Unit test

Questions

Will it cause performance regression or break compatibility?

No expected compatibility impact. The additional clear(...) is O(n) over resolved events and happens on the flush path; it prevents unbounded memory growth and improves stability under long-running workloads.

Do you need to update user documentation, design documentation or monitoring documentation?

No.

Release note

Fix a memory retention issue in kafka-consumer/pulsar-consumer that could cause unbounded memory growth and OOM under long-running workloads.

[gemini-code-assist]

Summary of Changes

Hello @wlwilliamx, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical memory retention issue within the Kafka and Pulsar consumers, which could lead to unbounded memory growth and potential Out-Of-Memory (OOM) errors in long-running workloads. The core solution involves a new ResolveInto method that ensures already-processed DML events are properly dereferenced, allowing Go's garbage collector to reclaim memory efficiently. Additionally, it refines logging levels to reduce noise under heavy system load, improving overall system stability and performance.

Highlights

• Memory Retention Fix: Introduced EventsGroup.ResolveInto to prevent Go GC memory retention of DMLEvents by copying resolved events to a destination slice and then explicitly clearing the pointers in the group's internal slice.
• Consumer Integration: Updated both Kafka and Pulsar consumers to utilize the new ResolveInto method when flushing events by watermark or before DDL execution, ensuring proper memory management.
• Logging Optimization: Reduced log verbosity by downgrading several high-frequency INFO/WARN level log messages to DEBUG level across consumer components.
• Unit Testing: Added comprehensive unit tests for EventsGroup.ResolveInto to ensure its correctness, validate pointer clearing, and prevent future memory retention regressions.

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[gemini-code-assist]

Code Review

This pull request effectively addresses a memory retention issue in the Kafka and Pulsar consumers by introducing a new EventsGroup.ResolveInto method. This method correctly copies out resolved events and clears the pointers in the backing array, preventing the Go garbage collector from retaining flushed DMLEvent objects. The changes are cleanly applied to both kafka-consumer and pulsar-consumer.

Additionally, the PR includes several beneficial log level reductions from INFO/WARN to DEBUG for high-frequency operations, which will help reduce log volume and improve performance under heavy workloads.

The new ResolveInto function is well-documented, and the accompanying unit tests are thorough, covering main functionality and edge cases, ensuring the correctness of the fix and preventing future regressions.

Overall, this is a high-quality contribution that improves the stability and performance of the consumers.

[wlwilliamx]

/test all

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: tenfyzhong, wk989898

The full list of commands accepted by this bot can be found here.

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Details

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• OWNERS [tenfyzhong,wk989898]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-01-30 10:34:49.945565707 +0000 UTC m=+1354117.559522553: ☑️ agreed by tenfyzhong.
• 2026-01-30 11:06:45.093596741 +0000 UTC m=+1356032.707553617: ☑️ agreed by wk989898.