* fix(admin): reduce memory usage and verbose logging for large clusters (#8919)
The admin server used excessive memory and produced thousands of log lines
on clusters with many volumes (e.g., 33k volumes). Three root causes:
1. Scanner duplicated all volume metrics: getVolumeHealthMetrics() created
VolumeHealthMetrics objects, then convertToTaskMetrics() copied them all
into identical types.VolumeHealthMetrics. Now uses the task-system type
directly, eliminating the duplicate allocation and removing convertToTaskMetrics.
2. All previous task states loaded at startup: LoadTasksFromPersistence read
and deserialized every .pb file from disk, logging each one. With thousands
of balance tasks persisted, this caused massive startup I/O, memory usage,
and log noise (including unguarded DEBUG glog.Infof per task). Now starts
with an empty queue — the scanner re-detects current needs from live cluster
state. Terminal tasks are purged from memory and disk when new scan results
arrive.
3. Verbose per-volume/per-node logging: V(2) and V(3) logs produced thousands
of lines per scan. Per-volume logs bumped to V(4), per-node/rack/disk logs
bumped to V(3). Topology summary now logs counts instead of full node ID arrays.
Also removes lastTopologyInfo field from MaintenanceScanner — the raw protobuf
topology is returned as a local value and not retained between 30-minute scans.
* fix(admin): delete stale task files at startup, add DeleteAllTaskStates
Old task .pb files from previous runs were left on disk. The periodic
CleanupCompletedTasks still loads all files to find completed ones —
the same expensive 4GB path from the pprof profile.
Now at startup, DeleteAllTaskStates removes all .pb files by scanning
the directory without reading or deserializing them. The scanner will
re-detect any tasks still needed from live cluster state.
* fix(admin): don't persist terminal tasks to disk
CompleteTask was saving failed/completed tasks to disk where they'd
accumulate. The periodic cleanup only triggered for completed tasks,
not failed ones. Now terminal tasks are deleted from disk immediately
and only kept in memory for the current session's UI.
* fix(admin): cap in-memory tasks to 100 per job type
Without a limit, the task map grows unbounded — balance could create
thousands of pending tasks for a cluster with many imbalanced volumes.
Now AddTask rejects new tasks when a job type already has 100 in the
queue. The scanner will re-detect skipped volumes on the next scan.
* fix(admin): address PR review - memory-only purge, active-only capacity
- purgeTerminalTasks now only cleans in-memory map (terminal tasks are
already deleted from disk by CompleteTask)
- Per-type capacity limit counts only active tasks (pending/assigned/
in_progress), not terminal ones
- When at capacity, purge terminal tasks first before rejecting
* fix(admin): fix orphaned comment, add TaskStatusCancelled to terminal switch
- Move hasQueuedOrActiveTaskForVolume comment to its function definition
- Add TaskStatusCancelled to the terminal state switch in CompleteTask
so cancelled task files are deleted from disk
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