[cuebot] Add memory stranded cores metric

[DiegoTavares]

Add three new prometheus metrics. cue_cores_total, cue_cores_idle cue_cores_memory_stranded. These metrics are intended to evaluate how many cores of the farm are being wasted per allocation due to not having enough memory to pick up more frames.

Summary by CodeRabbit

• New Features
  • Prometheus monitoring now exports per-allocation core metrics: total, idle, and memory-stranded cores for active hosts.
• Configuration
  • Metrics collector wired to host data so stranded-core values are included in metric exports.
• Tests
  • Added tests to validate stranded-core statistics and per-allocation reporting.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 60199483-0951-449a-a901-ed12c070432e

📥 Commits

Reviewing files that changed from the base of the PR and between e6d0ef5 and cfea074.

📒 Files selected for processing (1)

• cuebot/src/main/java/com/imageworks/spcue/StrandedCoreStats.java

🚧 Files skipped from review as they are similar to previous changes (1)

• cuebot/src/main/java/com/imageworks/spcue/StrandedCoreStats.java

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📝 Walkthrough

Walkthrough

This PR introduces per-allocation stranded core statistics that are collected from the database and exposed as Prometheus gauge metrics. The changes add a new data model, DAO query, service layer, metrics collection logic, Spring wiring, and test coverage to measure memory-constrained cores across allocations.

Changes

Memory-stranded Core Metrics Collection

Layer / File(s)	Summary
Data contract for stranded core statistics cuebot/src/main/java/com/imageworks/spcue/StrandedCoreStats.java	Defines StrandedCoreStats with public final fields for allocation name and three core counts (total, idle, stranded) in units of 100, including Javadoc describing the metric semantics.
DAO layer for stranded core statistics cuebot/src/main/java/com/imageworks/spcue/dao/HostDao.java, cuebot/src/main/java/com/imageworks/spcue/dao/postgres/HostDaoJdbc.java	Exposes getStrandedCoreStats() in HostDao interface and implements it in HostDaoJdbc with a SQL query that aggregates per-allocation core metrics from host_stat joined with alloc, filtering by memory threshold and host/lock states, mapping results to StrandedCoreStats objects.
Service layer for stranded core statistics cuebot/src/main/java/com/imageworks/spcue/service/HostManager.java, cuebot/src/main/java/com/imageworks/spcue/service/HostManagerService.java	Adds getStrandedCoreStats() method to HostManager interface and implements it in HostManagerService as a read-only transactional method that delegates to the DAO layer.
Prometheus metrics collection and exposure cuebot/src/main/java/com/imageworks/spcue/PrometheusMetricsCollector.java	Adds Log4j logging, a HostManager field, and three Prometheus gauges (cue_cores_total, cue_cores_idle, cue_cores_memory_stranded) labeled by environment, host, and allocation. Extends collectPrometheusMetrics() to fetch stranded core stats, scale from per-100 units to whole cores, clear and repopulate gauges, and catch/log errors without disrupting queue metrics. Adds setHostManager(...) setter.
Spring dependency configuration cuebot/src/main/resources/conf/spring/applicationContext-service.xml	Wires the hostManager bean as a property dependency on the prometheusMetricsCollector bean.
DAO layer test coverage cuebot/src/test/java/com/imageworks/spcue/test/dao/postgres/HostDaoTests.java	Adds testGetStrandedCoreStats to verify stranded core stats before and after changing idle memory, asserting total cores, idle cores, stranded cores transition, and allocation names. Includes findAllocStats helper to locate allocation stats in results.

Sequence Diagram(s)

sequenceDiagram
  participant PrometheusMetricsCollector
  participant HostManager
  participant HostManagerService
  participant HostDaoJdbc
  participant Database
  PrometheusMetricsCollector->>HostManager: getStrandedCoreStats()
  HostManager->>HostManagerService: delegate getStrandedCoreStats()
  HostManagerService->>HostDaoJdbc: getStrandedCoreStats()
  HostDaoJdbc->>Database: execute GET_STRANDED_CORE_STATS SQL
  Database-->>HostDaoJdbc: result rows
  HostDaoJdbc-->>HostManagerService: List<StrandedCoreStats>
  HostManagerService-->>HostManager: List<StrandedCoreStats>
  HostManager-->>PrometheusMetricsCollector: List<StrandedCoreStats>

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested reviewers

• lithorus
• ramonfigueiredo

🐰 Stranded cores now take center stage,
From database pools to Prometheus gauge,
Allocation by allocation they're tracked,
Memory-starved metrics fully unpacked! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ 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 clearly and concisely summarizes the main change: adding a new memory stranded cores metric to cuebot, which aligns with all file changes and the PR's core objective.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@cuebot/src/main/java/com/imageworks/spcue/PrometheusMetricsCollector.java`:
- Around line 281-284: The stranded-core gauges (coresTotal, coresIdle,
coresMemoryStranded) are being cleared before calling
hostManager.getStrandedCoreStats(), so if that DAO call fails we drop all
series; change the flow to first call hostManager.getStrandedCoreStats() and
capture the result (handle exceptions), and only clear and repopulate the three
gauges after the read succeeds (e.g. if stats list is non-null/returned without
exception), using the same variables coresTotal, coresIdle, coresMemoryStranded
to update values; this preserves existing series on DAO failure.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: ab649a14-dd59-4b14-8c44-a1ca05dca291

📥 Commits

Reviewing files that changed from the base of the PR and between 50a6044 and f1dde8e.

📒 Files selected for processing (8)

• cuebot/src/main/java/com/imageworks/spcue/PrometheusMetricsCollector.java
• cuebot/src/main/java/com/imageworks/spcue/StrandedCoreStats.java
• cuebot/src/main/java/com/imageworks/spcue/dao/HostDao.java
• cuebot/src/main/java/com/imageworks/spcue/dao/postgres/HostDaoJdbc.java
• cuebot/src/main/java/com/imageworks/spcue/service/HostManager.java
• cuebot/src/main/java/com/imageworks/spcue/service/HostManagerService.java
• cuebot/src/main/resources/conf/spring/applicationContext-service.xml
• cuebot/src/test/java/com/imageworks/spcue/test/dao/postgres/HostDaoTests.java

[ramonfigueiredo]

Thanks, @DiegoTavares

Approved with 2 minor changes required/suggested.

• Missing the Apache license header in two files.