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mattlord merged 2 commits into from
Jan 7, 2026
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docs: Add changelog entry for QueryThrottler observability metrics #19036

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Add changelog entry for QueryThrottler observability metrics
promptless[bot] Dec 16, 2025
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Merge remote-tracking branch 'origin/main' into promptless/pr-18740-q…
mattlord Jan 7, 2026
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16 changes: 16 additions & 0 deletions changelog/24.0/24.0.0/summary.md
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Expand Up @@ -14,6 +14,7 @@
- [JSON_EXTRACT now supports dynamic path arguments](#query-serving-json-extract-dynamic-args)
- **[VTTablet](#minor-changes-vttablet)**
- [New Experimental flag `--init-tablet-type-lookup`](#vttablet-init-tablet-type-lookup)
- [QueryThrottler Observability Metrics](#vttablet-querythrottler-metrics)
- [New `in_order_completion_pending_count` field in OnlineDDL outputs](#vttablet-onlineddl-in-order-completion-count)
- [Tablet Shutdown Tracking and Connection Validation](#vttablet-tablet-shutdown-validation)
- **[VTOrc](#minor-changes-vtorc)**
Expand Down Expand Up @@ -75,6 +76,21 @@ When enabled, the tablet uses its alias to look up the tablet type from the exis

**Note**: Vitess Operator–managed deployments generally do not keep tablet records in the topo between restarts, so this feature will not take effect in those environments.

#### <a id="vttablet-querythrottler-metrics"/>QueryThrottler Observability Metrics</a>

VTTablet now exposes new metrics to track QueryThrottler behavior.

Four new metrics have been added:

- **QueryThrottlerRequests**: Total number of requests evaluated by the query throttler
- **QueryThrottlerThrottled**: Number of requests that were throttled
- **QueryThrottlerTotalLatencyNs**: Total time each request takes in query throttling, including evaluation, metric checks, and other overhead (nanoseconds)
- **QueryThrottlerEvaluateLatencyNs**: Time taken to make the throttling decision (nanoseconds)

All metrics include labels for `Strategy`, `Workload`, and `Priority`. The `QueryThrottlerThrottled` metric has additional labels for `MetricName`, `MetricValue`, and `DryRun` to identify which metric triggered the throttling and whether it occurred in dry-run mode.

These metrics help monitor throttling patterns, identify which workloads are throttled, measure performance overhead, and validate behavior in dry-run mode before configuration changes.

#### <a id="vttablet-onlineddl-in-order-completion-count"/>New `in_order_completion_pending_count` field in OnlineDDL outputs</a>

OnlineDDL migration outputs now include a new `in_order_completion_pending_count` field. When using the `--in-order-completion` flag, this field shows how many migrations must complete before the current migration. The field is visible in `SHOW vitess_migrations` queries and `vtctldclient OnlineDDL <db> show` outputs.
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