Monitoring

Every database call (filter, sort, latency, exception, explain plan) is captured by the built-in IDatabaseMonitor. The monitor tracks collection metadata such as document counts, sizes, indexes and clean status. By default it persists state to a _monitor collection in MongoDB so data survives restarts and is shared across instances.

Storage modes

Mode	Behaviour
`Database` (default)	Persists to the `_monitor` collection. State survives restarts.
`Memory`	In-memory only. State is lost on restart.

Configure via appsettings.json:

"MongoDB": {
  "Monitor": {
    "Enabled": true,
    "StorageMode": "Database",
    "LastCallsToKeep": 1000,
    "SlowCallsToKeep": 200
  }
}

Or by code via services.AddMongoDB(o => o.Monitor = new MonitorOptions { ... }).

Source identification

All monitoring data is tagged with a source name. Default: {MachineName}/{AssemblyName}. Override via Monitor.SourceName. The Blazor call view shows a Source column when calls from multiple sources are present.

Command monitoring

Enable driver-level command timing to see how much of "Action" time is real MongoDB server time vs thread-pool wait. Disabled by default; enable with Monitor.EnableCommandMonitoring = true. Steps then include breakdowns like:

FetchCollection: Driver: listIndexes 2.10ms | Other: 0.45ms
Action: Driver: find 12.34ms | Other: 3.21ms

Useful for distinguishing slow database from slow serialization or application contention.

Centralised monitoring

For a single dashboard pane covering many MongoDB-talking services, install Tharga.MongoDB.Monitor.Client on each agent and Tharga.MongoDB.Monitor.Server on the central server.

Agent:

builder.AddMongoDB();
builder.AddMongoDbMonitorClient(sendTo: "https://monitor-server", apiKey: "...");

Server:

builder.AddMongoDB();
builder.AddMongoDbMonitorServer(primaryApiKey: "...");

var app = builder.Build();
app.UseMongoDbMonitorServer();

Agents push call events fire-and-forget over Tharga.Communication (SignalR-backed). The server ingests them into its local IDatabaseMonitor so the Blazor admin UI renders local + remote data side by side. When the server is unavailable or not configured, the agent has zero overhead.

API key rotation

Configure both primaryApiKey and secondaryApiKey on the server during a rotation window — either is accepted. Agents can also load keys from appsettings.json or User Secrets via the Tharga:Communication:ApiKey configuration path.

Remote action delegation

When the server dashboard displays collections from remote agents, actions like touch, drop index, restore index, clean are automatically delegated to the agent that owns the collection. No extra configuration — if Monitor.Client and Monitor.Server are installed, it works out of the box.

Live subscriptions

Live data (queue depth, ongoing calls) is only forwarded when someone is actively viewing the relevant tab. Blazor components subscribe on mount and unsubscribe on dispose. Collection metadata and completed calls are always forwarded.

Reset

IDatabaseMonitor.ResetAsync() clears all cached state (in-memory + persisted). The Blazor CollectionView exposes a Reset button that calls this.

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