Probe Types & Instrumentation Catalog

InSitu supports four specialized, ultra-lightweight probe types. Each probe is optimized for a different stage of production debugging and telemetry tracking.

⚡ Comparison of Probe Capabilities

Probe Type	What it captures	CPU Overhead	Memory Overhead	Payload Size	Best for
Snapshot	Local variables, watch expressions, full call stack	Low (microseconds)	Low	~50KB-500KB	Inspecting complex state bugs, null-pointer exceptions, payload structures
Dynamic Log	Formatted string with interpolated runtime values	Very Low	Very Low	Low (< 1KB)	Adding telemetry on-the-fly, checking thread execution, debugging routing
Counter	Numeric hit increment	Negligible	None	Raw Integer	Tracking hot paths (loops, cache misses) without log spam
Custom Metric	Evaluated float value of any expression	Negligible	None	Raw Float	Tracking latency ratios, queue depths, pool capacities

📸 1. Snapshot Probes

Snapshot probes capture variables and call stack frames when execution reaches a line, without stopping the application in a debugger. Capture adds work to your application.

How to Configure Snapshots

Hit Limit (Default 1): Limits how many snapshots are taken before the probe automatically uninstalls itself in-process. snapshots default to 1 to avoid heap copies.
Watch Expressions: Enter custom evaluations (e.g. user.profile.isAdmin) to track deep nested values without serializing entire root objects.
Condition: Filter the execution. Only captures when a boolean evaluation is met (e.g., cart.total > 5000).

📝 2. Dynamic Log Probes

Dynamic Log probes let you write log lines with interpolated variables (${expression}) and inject them into stdout/stderr without redeploying.

message Formatting Syntax

Wrap runtime variables in standard string interpolation templates:

Processing purchase for user: ${user.id} | Items in cart: ${cart.items.length}

Supported Log Levels

INFO - Standard operational traces.
WARN - Unexpected but non-fatal conditions.
ERROR - Critical failures and exceptions.
DEBUG - High-detail engineering diagnostics.

🔢 3. Counter Probes

Counter probes are extremely lightweight. Instead of collecting strings or variable trees, they increment a running atomic counter in-process and stream the frequency of execution back to your editor.

Key Use Cases

Measuring branch execution (e.g., how often is the else block running versus the if block?).
Tracking cache misses inside database queries.
Measuring high-frequency loops (perfectly safe for paths executing millions of times per second).

📈 4. Custom Metrics Probes

Metric probes evaluate any mathematical or numerical expression and export the float result directly to your editor or metric dashboard.

Example Expressions

databasePool.activeConnections
(endTime - startTime) / 1000
user.orders.count

Conditionals & Hit Limits

Because metrics and counters generate minimal network payloads, their default hit limits can be scaled much higher (up to 10,000 hits) than Snapshots to build high-fidelity frequency charts.

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