feat: add optional seconds field to cron schedule parsing

[christinoleo]

Summary

Enables sub-minute scheduling by adding SecondOptional to the cron parser. This allows schedules like */5 * * * * * to run every 5 seconds.

Changes

• Add cron.SecondOptional flag to parser in spec/schedule.go
• Update scheduler tick precision from minute to second
• Update NextTick to advance by seconds instead of minutes
• Update dagrunjob to use second-level truncation

Motivation

As discussed in #676, the underlying robfig/cron library already supports seconds parsing via the SecondOptional flag. This PR enables that functionality.

Usage

Standard 5-field cron expressions continue to work as before:

schedule: "*/5 * * * *"  # Every 5 minutes

With this change, 6-field expressions with seconds are now supported:

schedule: "*/5 * * * * *"  # Every 5 seconds

Fixes #676

Summary by CodeRabbit

• New Features

  • Scheduling granularity increased from minute-based to second-based, enabling more frequent task execution. Cron expressions now support optional seconds fields for enhanced scheduling precision and control.

• Chores

  • Updated configuration files.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

The changes enable second-level precision in cron expressions by adding cron.SecondOptional to the cron parser configuration and updating scheduler tick granularity from minute-based to second-based alignment, allowing jobs to be scheduled at sub-minute intervals.

Changes

Cohort / File(s)	Summary
Cron Parser Configuration internal/core/spec/schedule.go, internal/service/scheduler/scheduler_test.go	Added cron.SecondOptional flag to enable optional seconds field parsing in cron expressions; test initialization updated to match production parser configuration.
Scheduler Tick Granularity internal/service/scheduler/scheduler.go	Changed tick alignment from minute-based (truncate to minute boundary) to second-based (truncate to second boundary); NextTick calculation now advances by 1 second instead of 60 seconds.
Job Timing Precision internal/service/scheduler/dagrunjob.go	Modified latestStartedAt normalization from minute precision to second precision, affecting timing comparisons in Ready method.
Metadata .gitignore	Added "dagu" to Go-related ignore rules.

Poem

🐰 A second-hand sprint through the cron-parser hall,
Where minutes once marched, now seconds enthrall!
Five-second health checks now dance in the queue,
Dagu keeps the beat, precise and so true! ✨

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main feature being added: optional seconds field support in cron schedule parsing.
Linked Issues check	✅ Passed	The PR fulfills issue #676's requirement by adding SecondOptional flag to the cron parser, enabling sub-minute scheduling with second-level precision as requested.
Out of Scope Changes check	✅ Passed	All changes are scoped to enabling seconds-precision scheduling: .gitignore, cron parser configuration, and scheduler tick calculations. No unrelated modifications detected.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

---

📜 Recent review details

Configuration used: defaults

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 140afba and bd9a3c6.

📒 Files selected for processing (5)

• .gitignore
• internal/core/spec/schedule.go
• internal/service/scheduler/dagrunjob.go
• internal/service/scheduler/scheduler.go
• internal/service/scheduler/scheduler_test.go

🧰 Additional context used

📓 Path-based instructions (2)

**/*.go

📄 CodeRabbit inference engine (AGENTS.md)

**/*.go: Backend entrypoint in cmd/ orchestrates the scheduler and CLI; runtime, persistence, and service layers sit under internal/* (for example internal/runtime, internal/persistence)
Keep Go files gofmt/goimports clean; use tabs, PascalCase for exported symbols (SchedulerClient), lowerCamelCase for locals, and Err... names for package-level errors
Repository linting relies on golangci-lint; prefer idiomatic Go patterns, minimal global state, and structured logging helpers in internal/common

Files:

• internal/core/spec/schedule.go
• internal/service/scheduler/scheduler.go
• internal/service/scheduler/scheduler_test.go
• internal/service/scheduler/dagrunjob.go

**/*_test.go

📄 CodeRabbit inference engine (AGENTS.md)

**/*_test.go: Co-locate Go tests as *_test.go; favour table-driven cases and cover failure paths
Use stretchr/testify/require and shared fixtures from internal/test instead of duplicating mocks

Files:

• internal/service/scheduler/scheduler_test.go

🔇 Additional comments (7)

.gitignore (1)

41-41: LGTM! Standard build artifact ignore.

Adding the dagu binary to .gitignore prevents committing the built executable.

internal/service/scheduler/dagrunjob.go (1)

96-96: LGTM! Necessary precision adjustment.

Changing from time.Minute to time.Second truncation aligns with the scheduler's new second-level tick granularity, ensuring correct comparisons for sub-minute schedules.

internal/service/scheduler/scheduler_test.go (2)

84-84: LGTM! Test parser aligned with production.

Correctly updated to include cron.SecondOptional flag, matching the production parser configuration.

---

195-195: LGTM! Test parser aligned with production.

Correctly updated to include cron.SecondOptional flag, matching the production parser configuration.

internal/service/scheduler/scheduler.go (2)

309-311: LGTM! Correct second-based tick advancement.

The NextTick implementation now correctly advances by one second instead of one minute, aligning with the second-level scheduling granularity introduced by cron.SecondOptional.

---

283-283: Verify performance impact of second-level tick granularity.

Changing from time.Minute to time.Second truncation means the scheduler now ticks 60 times more frequently. This is necessary for sub-minute scheduling but increases CPU usage.

The impact should be minimal when no jobs are scheduled for a given second, but for deployments with many DAGs, the increased frequency of invokeJobs and entryReader.Next calls could be noticeable.

Consider profiling the scheduler under production-like load to verify the performance impact is acceptable:

#!/bin/bash
# Compare CPU usage before/after this change with a representative DAG count
echo "Profile the scheduler with multiple DAGs scheduled at different intervals:"
echo "1. Set up test environment with 100+ DAGs (mix of minute and second schedules)"
echo "2. Monitor CPU usage over 5-10 minutes"
echo "3. Compare against baseline with minute-only schedules"
echo ""
echo "Use Go's pprof if available:"
echo "  go tool pprof -http=:8080 http://localhost:6060/debug/pprof/profile?seconds=30"

internal/core/spec/schedule.go (1)

10-12: The cron.SecondOptional flag correctly enables optional seconds parsing.

The addition of cron.SecondOptional to the parser flags allows both 5-field (minute precision) and 6-field (second precision) cron expressions while maintaining backward compatibility. This is the standard approach in robfig/cron v3.0.1 for supporting sub-minute scheduling as intended by the PR.

---

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[coderabbitai]

Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

internal/service/scheduler/scheduler_test.go (1)

71-80: Critical: Test expectations don't match new second-based behavior.

The NextTick test expects minute-granularity behavior (advancing from 01:00:50 to 01:01:00), but the implementation now uses second-granularity (NextTick returns now.Add(time.Second).Truncate(time.Second)), which would advance to 01:00:51.

This test should be failing unless the expected result is updated to match the new second-based tick advancement.

🔎 Proposed fix

 	t.Run("NextTick", func(t *testing.T) {
 		now := time.Date(2020, 1, 1, 1, 0, 50, 0, time.UTC)
 
 		th := test.SetupScheduler(t)
 		schedulerInstance, err := scheduler.New(th.Config, &mockJobManager{}, th.DAGRunMgr, th.DAGRunStore, th.QueueStore, th.ProcStore, th.ServiceRegistry, th.CoordinatorCli)
 		require.NoError(t, err)
 
 		next := schedulerInstance.NextTick(now)
-		require.Equal(t, time.Date(2020, 1, 1, 1, 1, 0, 0, time.UTC), next)
+		require.Equal(t, time.Date(2020, 1, 1, 1, 0, 51, 0, time.UTC), next)
 	})

📜 Review details

Configuration used: defaults

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 140afba and bd9a3c6.

📒 Files selected for processing (5)

• .gitignore
• internal/core/spec/schedule.go
• internal/service/scheduler/dagrunjob.go
• internal/service/scheduler/scheduler.go
• internal/service/scheduler/scheduler_test.go

🧰 Additional context used

📓 Path-based instructions (2)

**/*.go

📄 CodeRabbit inference engine (AGENTS.md)

**/*.go: Backend entrypoint in cmd/ orchestrates the scheduler and CLI; runtime, persistence, and service layers sit under internal/* (for example internal/runtime, internal/persistence)
Keep Go files gofmt/goimports clean; use tabs, PascalCase for exported symbols (SchedulerClient), lowerCamelCase for locals, and Err... names for package-level errors
Repository linting relies on golangci-lint; prefer idiomatic Go patterns, minimal global state, and structured logging helpers in internal/common

Files:

• internal/core/spec/schedule.go
• internal/service/scheduler/scheduler.go
• internal/service/scheduler/scheduler_test.go
• internal/service/scheduler/dagrunjob.go

**/*_test.go

📄 CodeRabbit inference engine (AGENTS.md)

**/*_test.go: Co-locate Go tests as *_test.go; favour table-driven cases and cover failure paths
Use stretchr/testify/require and shared fixtures from internal/test instead of duplicating mocks

Files:

• internal/service/scheduler/scheduler_test.go

🔇 Additional comments (7)

.gitignore (1)

41-41: LGTM! Standard build artifact ignore.

Adding the dagu binary to .gitignore prevents committing the built executable.

internal/service/scheduler/dagrunjob.go (1)

96-96: LGTM! Necessary precision adjustment.

Changing from time.Minute to time.Second truncation aligns with the scheduler's new second-level tick granularity, ensuring correct comparisons for sub-minute schedules.

internal/service/scheduler/scheduler_test.go (2)

84-84: LGTM! Test parser aligned with production.

Correctly updated to include cron.SecondOptional flag, matching the production parser configuration.

---

195-195: LGTM! Test parser aligned with production.

Correctly updated to include cron.SecondOptional flag, matching the production parser configuration.

internal/service/scheduler/scheduler.go (2)

309-311: LGTM! Correct second-based tick advancement.

The NextTick implementation now correctly advances by one second instead of one minute, aligning with the second-level scheduling granularity introduced by cron.SecondOptional.

---

283-283: Verify performance impact of second-level tick granularity.

Changing from time.Minute to time.Second truncation means the scheduler now ticks 60 times more frequently. This is necessary for sub-minute scheduling but increases CPU usage.

The impact should be minimal when no jobs are scheduled for a given second, but for deployments with many DAGs, the increased frequency of invokeJobs and entryReader.Next calls could be noticeable.

Consider profiling the scheduler under production-like load to verify the performance impact is acceptable:

#!/bin/bash
# Compare CPU usage before/after this change with a representative DAG count
echo "Profile the scheduler with multiple DAGs scheduled at different intervals:"
echo "1. Set up test environment with 100+ DAGs (mix of minute and second schedules)"
echo "2. Monitor CPU usage over 5-10 minutes"
echo "3. Compare against baseline with minute-only schedules"
echo ""
echo "Use Go's pprof if available:"
echo "  go tool pprof -http=:8080 http://localhost:6060/debug/pprof/profile?seconds=30"

internal/core/spec/schedule.go (1)

10-12: The cron.SecondOptional flag correctly enables optional seconds parsing.

The addition of cron.SecondOptional to the parser flags allows both 5-field (minute precision) and 6-field (second precision) cron expressions while maintaining backward compatibility. This is the standard approach in robfig/cron v3.0.1 for supporting sub-minute scheduling as intended by the PR.