metrics: add redo metrics

[wk989898]

What problem does this PR solve?

Issue Number: ref #1061

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[gemini-code-assist]

Summary of Changes

Hello @wk989898, 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 enhances the observability of the redo sink component by introducing a comprehensive set of new metrics. It centralizes metric collection within a dedicated structure, allowing for more granular tracking of redo log operations and worker performance. The changes also ensure that monitoring dashboards accurately reflect these new and refined metrics, providing better insights into the redo sink's behavior.

Highlights

• New Redo Sink Metrics: Introduced a dedicated redoSinkMetrics struct to encapsulate and manage various metrics related to the redo sink, including write durations for rows and DDLs, total row and DDL counts, and worker busy ratios.
• Metric Collection Refactoring: Refactored the Sink component to utilize the new redoSinkMetrics for observing DDL and DML write operations, replacing the previous generic statistics object.
• Grafana Dashboard Updates: Updated existing Grafana dashboard configurations to align with the new metric names and corrected the calculation for the ticdc_redo_worker_busy_ratio metric.

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Changelog

• downstreamadapter/sink/redo/metrics.go
  • Added a new file defining the redoSinkMetrics struct and its associated methods for initializing, observing, and closing redo sink metrics.
• downstreamadapter/sink/redo/sink.go
  • Removed the direct import of pkg/metrics as metric handling is now localized.
  • Replaced the statistics field with a metric field of type redoSinkMetrics in the Sink struct.
  • Initialized the new metric field in the New function.
  • Modified WriteBlockEvent to record DDL write duration using the new redoSinkMetrics.
  • Removed the statistics.RecordBatchExecution call from AddDMLEvent.
  • Updated the Close method to call the close method on the new redoSinkMetrics instance.
  • Modified sendMessages to record row write duration using the new redoSinkMetrics.
• metrics/grafana/ticdc_new_arch.json
  • Updated the Prometheus expression for ticdc_redo_flushall_duration_seconds_bucket to ticdc_redo_flush_all_duration_seconds_bucket.
  • Corrected the calculation for ticdc_redo_worker_busy_ratio from division by 10 to multiplication by 100.
• metrics/nextgengrafana/ticdc_new_arch_next_gen.json
  • Updated the Prometheus expression for ticdc_redo_flushall_duration_seconds_bucket to ticdc_redo_flush_all_duration_seconds_bucket.
  • Corrected the calculation for ticdc_redo_worker_busy_ratio from division by 10 to multiplication by 100.
• pkg/metrics/redo.go
  • Added RedoTotalRowsCountGauge to track the total number of rows written to the redo log.
  • Added RedoWriteLogDurationHistogram to measure the latency of write log operations.
  • Added RedoWorkerBusyRatio to monitor the busy ratio of the redo sink worker.
  • Registered the newly introduced metrics in the initRedoMetrics function.

Activity

• The pull request was opened by wk989898.
• The pull request references issue Add redo support #1061, indicating a related problem or feature request.

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[gemini-code-assist]

Code Review

This pull request introduces new metrics for the redo log sink, replacing the generic statistics collector. The changes include adding new Prometheus metrics for redo log operations, integrating them into the redo sink, and updating Grafana dashboards to use these new metrics. My review focuses on the correctness of the new metrics implementation and potential regressions. I've identified a potential regression where batch-level metrics are no longer reported, and a couple of areas for improvement in the new metrics code.

[gemini-code-assist]

By removing statistics.RecordBatchExecution, we've lost valuable batch-level metrics such as ExecBatchHistogram (batch size in rows) and ExecBatchWriteBytesHistogram (batch size in bytes). While new per-row metrics are added, these batch metrics are important for monitoring and performance tuning. Was this intentional? If not, please consider reintroducing them or providing an equivalent.

[gemini-code-assist]

The copyright year is set to 2026, which is in the future. Please correct it to the current year.

Suggested change

	// Copyright 2026 PingCAP, Inc.
	// Copyright 2024 PingCAP, Inc.