---
id: "bug-1931"
status: "open"
status_updated: "2026-10-09"
status_note: "newly logged"
component: "scheduler"
severity: "wrong-result"
timestamp: "2026-10-09T07:23:49Z"
last_seen: "2026-10-09T07:23:49Z"
occurrences: 1
files: ["src/scheduler/src/plugins/parjob_allocator.c", "src/scheduler/src/alloc_runner.c"]
tags: ["scheduler", "parjob", "allocation", "mintasks"]
related: []
---

# bug-1931: xce_scheduler parjob allocator ignores minTasks: a tasks 2..5 job pends though 2 slots are free

## Description
**Observed:** in a `xce_scheduler --sim` session, element `[5]` of an array job requesting `tasks 2..5` pends although its only candidate host, pc13v, has 2 free slots (22 total, 20 in use by elements [1]-[4], 5 tasks each). The decision trace shows that only 5-task partitions are tried:
```
[trace] job 0-5-1791529946-0[5]  session 23  position 5  level full
  requirement single  tasks 2..5  requests mem=409600.000000 (400.00 KB)
    plan 1  hosts 1  tasks per position [5]
        host pc13v  rejected (per-host check): resource shortfall
          slots total 22 in-use 20 reserved 0 requested 5
    plan 2  hosts 2  tasks per position [3, 2]
        host pc13v  rejected (per-host check): resource shortfall
          slots total 22 in-use 20 reserved 0 requested 3
    plan 3  hosts 3  tasks per position [2, 2, 1]
        host pc13v  accepted
        ...
    plans: 5 generated, 5 tried, 0 discarded, 0 not tried; no plan could be placed
  outcome: PEND
    host pc13v: resource slots: NO_RESOURCE
```
**Expected:** a job with `minTasks=2, maxTasks=5` is placed with any task count in 2..5 that fits, preferring the largest; here 2 tasks on pc13v (plan `[2]`). If even `minTasks` tasks cannot be placed, the job pends.
**Impact:** every parallel job submitted with a task range (`minTasks < maxTasks`) is scheduled as if `minTasks == maxTasks`: it pends until `maxTasks` tasks fit, wasting free capacity and delaying the job indefinitely on a busy cluster. Wrong scheduling result, no crash.
**Found by:** user review of the sim decision trace (2026-10-09).
## Environment
- OS: no /etc/os-release; Docker container; NixOS kernel; kernel Linux 6.18.33 x86_64
- libc: not recorded: the failing `xce_scheduler` binary is not in this checkout (no build dir); host ldd reports glibc 2.40. The defect is in allocator logic and does not depend on libc
- Toolchain: gcc (GCC) 15.2.0, meson 1.9.1
- Build: profile not recorded (asan, debug or release unknown; user's sim session); the defect is profile-independent allocator logic
- Code: scheduler-framework @ a64d0846-dirty
- Deployment: `xce_scheduler --sim` (sim session 23), one simulated worker pc13v (22 slots), queue xce, policy builtin_fcfs

## Reproduction
1. In `xce_scheduler --sim`, set up one worker with 22 slots and submit an array job of at least 5 elements, each with `minTasks=2, maxTasks=5` (any small mem request, e.g. 400 KB).
2. `trace on all`, then run a scheduling session: elements [1]-[4] start with 5 tasks each (20 slots used).
3. Element [5] pends; its trace lists only partitions of 5 tasks, never `[2]`, `[3]` or `[4]`.
4. Code-level check: `parjob_plan_iter_init()`/`parjob_plan_iter_next()` (`src/scheduler/src/plugins/parjob_allocator.c:202-288`) read only `resreq->maxTasks`; no allocator reads `minTasks` (`grep -rn minTasks src/scheduler/src` shows only the trace and cache-fingerprint fields).
- Frequency: deterministic
- Evidence: decision trace quoted above (from the user's sim session); session not saved
## Root cause
TODO: required for fixed/partial

## Fix
TODO: required for fixed/partial

## Verification
- Test: TODO: name + file; RED before the fix, GREEN after
- Suites: TODO: suite results and build profile
- Live: TODO: soak/deploy run, or n/a and why

## References
- Related: bug-1770 (wired real minTasks/maxTasks into the primary resreq; the allocator never consumed minTasks), bug-1932 (same trace; unsatisfiable cache not used in sim)
- Docs: .kiro/specs/scheduler-allocation/requirements.md (Req 4 AC 1), .kiro/specs/resreq-maxtasks-wiring/, .kiro/specs/parjob-capacity-partitioning/