feat: add failed and slow queries to query stats

[davidby-influx]

Add

statQueriesFailed = "queriesFailed" // Number of queries that have failed.
statQueriesSlow = "queriesSlow" // Snapshot of in-flight queries running longer than log-queries-after.

Closes https://github.com/influxdata/feature-requests/issues/392

[Copilot]

Pull request overview

This PR extends the query executor’s _internal query statistics by adding two new metrics: total failed queries and a snapshot count of currently-running “slow” queries (running longer than log-queries-after). This aligns runtime monitoring with existing slow-query logging semantics and provides better observability for query failures.

Changes:

• Add queriesFailed stat and increment it based on terminal errors, execution-context-emitted errors, and panics.
• Add queriesSlow stat by computing an in-flight slow-query snapshot from the TaskManager using LogQueriesAfter.
• Add unit tests covering queriesFailed counting behavior and SlowQueryCount() behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
query/task_manager.go	Adds SlowQueryCount() to snapshot in-flight queries exceeding LogQueriesAfter.
query/executor.go	Adds queriesFailed / queriesSlow stats and wires counting into execution + panic recovery paths.
query/executor_test.go	Adds tests for queriesFailed semantics and slow-query snapshot counting.
query/execution_context.go	Tracks whether an error Result has been sent/attempted via a new atomic failed flag.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

query/executor.go:394

• This error Result is sent directly on results without setting StatementID (so multi-statement queries can report the error against statement 0) and without honoring AbortCh (so a caller aborting can still leave this goroutine blocked on send). Use ctx.send with StatementID: i so AbortCh is respected and the statement index is correct.

						failed = true
						results <- &Result{
							Err: fmt.Errorf("unable to use system source '%s': use %s instead", s.Name, command),
						}
						break LOOP

[devanbenz]

Just one comment about failed vs cancelled/interrupted queries.

[devanbenz]

Should we consider a cancelled query as failed? Or should we use a different metric for this i.e. CancelledQueries?

[davidby-influx]

I think canceled queries will be such a small percentage, we can consider them failed because of user unhappiness.

[devanbenz]

LGTM