Performance diagnosis

Monte Carlo Performance Diagnosis Skill

This skill helps diagnose data pipeline performance issues using Monte Carlo's cross-platform observability data. It works across Airflow, dbt, Databricks, and warehouse query engines to find bottlenecks, detect regressions, and identify root causes.

Monte Carlo tool routing (required): Always call Monte Carlo MCP tools through this plugin's bundled server, whose fully-qualified tool names are mcp__plugin_mc-agent-toolkit_monte-carlo-mcp__<tool> (e.g. mcp__plugin_mc-agent-toolkit_monte-carlo-mcp__get_alerts). Bare tool names used in this skill (get_alerts, search, get_table, …) refer to that bundled server. If the session also has a separately-configured monte-carlo-mcp server, do not route to it — it may point at a different endpoint or credentials.

Reference files live next to this skill file. Use the Read tool (not MCP resources) to access them:

• Tiered investigation approach: references/investigation-tiers.md (relative to this file)
• Query analysis patterns: references/query-analysis.md (relative to this file)

When to activate this skill

Activate when the user:

• Asks about slow pipelines, jobs, or queries
• Wants to find expensive or costly queries
• Mentions performance regressions or degradation
• Asks "why is this pipeline slow?" or "what's using the most compute?"
• Wants to compare performance over time or find bottleneck tasks
• Asks about failed or futile query patterns

When NOT to activate this skill

Do not activate when the user is:

• Investigating data quality issues (use the prevent skill)
• Looking at storage costs (use the storage-cost-analysis skill)
• Creating monitors (use the monitoring-advisor skill)
• Just querying data or exploring table contents

Prerequisites

The following MCP tools must be available (connect to Monte Carlo's MCP server):

Discovery tools (Tier 1):

• get_jobs_performance -- find slow/failing jobs across Airflow, dbt, Databricks
• get_top_slow_queries -- find slowest query groups by total runtime

Bridge tool:

• get_tables_for_job -- convert job MCONs to table MCONs

Diagnosis tools (Tier 2):

• get_tasks_performance -- drill into a job's individual tasks
• get_change_timeline -- unified timeline of query changes, volume shifts, Airflow/dbt failures
• get_query_rca -- root cause analysis for failed/futile queries
• get_query_latency_distribution -- latency trend over time
• get_asset_lineage -- trace upstream/downstream impact

Supporting tools:

• get_warehouses -- list available warehouses

Workflow

Step 1: Identify the scope

Determine what the user wants to investigate:

• Specific job/pipeline: User mentions a job name or pipeline
• Specific table: User mentions a table that's slow to update
• General discovery: User wants to find what's slow

Call get_warehouses to list available warehouses. Match the user's context to a warehouse.

Step 2: Tier 1 -- Discovery

If you don't have specific MCONs to investigate, start with discovery:

1. Find slow jobs: Call get_jobs_performance with optional integration_type filter (AIRFLOW, DATABRICKS, DBT) if the user specifies a platform.

   • Results include: job name, average duration, trend (7-day), run count, failure rate
   • Look for: high avgDuration, negative runDurationTrend7d, high failure rates

2. Find expensive queries: Call get_top_slow_queries with optional warehouse_id and query_type ("read" for SELECTs, "write" for INSERT/CREATE/MERGE).

   • Results include: query hash, total runtime, average runtime, run count
   • Look for: queries with high total runtime or high individual execution time

Present the top findings to the user before drilling deeper. A typical investigation needs only 3-7 tool calls.

If both discovery tools return no results: Tell the user no performance issues were found in the current time window. Suggest broadening the scope (different warehouse, longer time range, or a different platform filter).

Step 3: Bridge -- Job to Tables

After Tier 1 identifies problematic jobs, convert to table MCONs:

Call get_tables_for_job(job_mcon=..., integration_type=...) using the integration_type from the job performance results.

This gives you the table MCONs needed for Tier 2 investigation.

Step 4: Tier 2 -- Diagnosis

Now drill into root causes using the MCONs from discovery or the bridge:

1. Task bottleneck: Call get_tasks_performance to find which specific task in a job is the bottleneck.

2. What changed? Call get_change_timeline -- this is your most powerful tool. It returns a unified timeline of:

   • Query text changes (schema modifications, new JOINs, filter changes)
   • Volume shifts (row count spikes/drops)
   • Airflow task failures
   • dbt model failures All in one call. Look for correlations: "query changed on day X, runtime doubled on day X+1."

3. Why are queries failing? Call get_query_rca to get root cause analysis:

   • Failed queries: errors, timeouts, permission issues
   • Futile queries: queries that run but produce no useful output
   • Patterns are pre-computed -- the tool groups failures by cause

4. Is latency degrading? Call get_query_latency_distribution to see the trend:

   • Compare p50 vs p95 -- if p95 >> p50 (>5x), the problem is outlier queries
   • Look for step-changes in latency (sudden increase = regression)
   • For step-change / regression-time-localization use cases, pass bucket="1h". The default downsamples to daily on windows ≥ 3 days, which hides hour-level steps.

5. Trace impact: Call get_asset_lineage with direction="DOWNSTREAM" to see what's affected by a slow table, or direction="UPSTREAM" to find what feeds it.

Step 5: Present findings

Structure your response as:

1. Problem summary: What's slow and by how much (with exact numbers from tools)
2. Root cause: What changed or what's causing the issue
3. Impact: What downstream systems are affected
4. Recommendations: Specific actions to fix the issue

Important rules

• Quote tool numbers exactly. If a tool returns "1282 runs, avg 22.5s", say exactly that. Never round, estimate, or fabricate numbers.
• Always compare to baselines. Use 7-day trend data (runDurationTrend7d) to distinguish regressions from normal variance. Flag if trend data has less than 0.1 confidence.
• Stop when you have a root cause. 3-7 tool calls is typical. More than 10 means you're over-investigating.
• Read vs write queries: When the user asks about "reads" or "read queries", filter with query_type="read". When they ask about "writes", use query_type="write". Do NOT mix them.
• Never expose MCONs, UUIDs, or internal identifiers to the user. Use human-readable names.
• Cross-platform: This skill works across Airflow, dbt, and Databricks. Note which platform each finding comes from.