[I] [server] Add disk-usage write protection to TabletServer [fluss]

["swuferhong (via GitHub)" <gi...@apache.org>]

swuferhong opened a new issue, #3338:
URL: https://github.com/apache/fluss/issues/3338

   ### Search before asking
   
   - [x] I searched in the [issues](https://github.com/apache/fluss/issues) and found nothing similar.
   
   
   ### Motivation
   
   When a TabletServer's local data disk is nearly full, continued writes can cause multiple errors, corrupt in-progress segments, or trigger cascading failures across replicas. Currently Fluss has no built-in mechanism to proactively reject writes before the disk runs out of space.
   
   ### Solution
   
   Introduce a periodic disk-usage monitoring state machine with hysteresis-based write protection:
   
   - Sampling: A background scheduler thread calls statvfs every `server.data-disk.check-interval` (default 30s) to collect the disk usage ratio. The overhead is negligible (~100μs per call, pure in-memory).
   - Multi-disk strategy: When multiple data directories are configured, the collector reports the maximum usage across all distinct FileStores, so that a single nearly-full disk is never masked by other low-usage disks.
   - Hysteresis state machine: Writes are locked when any disk's usage reaches server.data-disk.write-limit-ratio (default 0.85) and resume only after usage drops below (ratio - 0.10). The fixed 10% recovery gap prevents rapid lock/unlock oscillation.
   - Write interception: Only client-driven writes (appendLog / putKv) are rejected with a retriable DiskWriteLockedException. Follower replication is not blocked to preserve replica consistency.
   - Dynamic reconfiguration: `server.data-disk.write-limit-ratio` can be changed at runtime via alterConfigs(). Changes take effect immediately by triggering a synchronous disk check.
   
   
   ### Anything else?
   
   _No response_
   
   ### Willingness to contribute
   
   - [x] I'm willing to submit a PR!


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Re: [I] [server] Add disk-usage write protection to TabletServer [fluss]

["wuchong (via GitHub)" <gi...@apache.org>]

wuchong closed issue #3338: [server] Add disk-usage write protection to TabletServer
URL: https://github.com/apache/fluss/issues/3338


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