HDDS-14041. Add metrics to track Snapshot RocksDB space and SST File stats.

[sadanand48]

What changes were proposed in this pull request?

Add metrics to track Snapshot RocksDB space and SST File stats

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-14041

How was this patch tested?

Tried out on docker

  "beans" : [ {
    "name" : "Hadoop:service=OzoneManager,name=OMSnapshotDirectoryMetrics",
    "modelerType" : "OMSnapshotDirectoryMetrics",
    "tag.Context" : "Snapshot Directory Metrics",
    "tag.Hostname" : "b8f9c29c90ba",
    "DbSnapshotsDirSize" : 1162516,
    "TotalSstFilesCount" : 36,
    "NumSnapshots" : 3,
    "tag.Context.1" : "Per-Checkpoint Directory Metrics",
    "tag.CheckpointDirName.1" : "om.db-094618c2-8b30-4220-8351-d7d9d9b18cbd",
    "tag.Hostname.1" : "b8f9c29c90ba",
    "CheckpointDirSize.1" : 374766,
    "CheckpointSstFilesCount.1" : 4,
    "tag.Context.2" : "Per-Checkpoint Directory Metrics",
    "tag.CheckpointDirName.2" : "om.db-d7be41db-47e3-4db6-b556-1c72e5a88825",
    "tag.Hostname.2" : "b8f9c29c90ba",
    "CheckpointDirSize.2" : 398392,
    "CheckpointSstFilesCount.2" : 20,
    "tag.Context.3" : "Per-Checkpoint Directory Metrics",
    "tag.CheckpointDirName.3" : "om.db-4ad9186b-bea9-4ed5-b052-1a301e539f3e",
    "tag.Hostname.3" : "b8f9c29c90ba",
    "CheckpointDirSize.3" : 387538,
    "CheckpointSstFilesCount.3" : 12
  } ]
}

[Copilot]

Pull request overview

This PR adds comprehensive metrics tracking for Ozone Manager's snapshot RocksDB directories, monitoring disk space usage and SST file counts. The implementation introduces a new metrics class that periodically collects statistics both at the aggregate level (total snapshots directory size and SST file count) and per-checkpoint directory level, with configurable update intervals.

Key Changes

• Introduces OMSnapshotDirectoryMetrics class with asynchronous metrics collection using a Timer-based scheduler
• Adds configuration property ozone.om.snapshot.directory.metrics.update.interval (default: 5 minutes) to control update frequency
• Integrates metrics lifecycle into OzoneManager's start/restart/stop methods

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 15 comments.

Show a summary per file

File	Description
OMSnapshotDirectoryMetrics.java	New metrics class implementing periodic collection of snapshot directory size and SST file statistics with both aggregate and per-checkpoint metrics
OzoneManager.java	Integrates snapshot directory metrics into OM lifecycle by starting metrics collection on start/restart and stopping on shutdown
OMMetrics.java	Adds snapshot directory metrics management methods and field to hold the metrics instance
OMConfigKeys.java	Defines configuration key and default value for metrics update interval
ozone-default.xml	Adds configuration property documentation for the metrics update interval setting

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