managing-duckdb

name	managing-duckdb
description	Use when working with Duckdb — duckDB database management, query performance analysis, extension management, and storage optimization. Covers database file inspection, table statistics, memory configuration, Parquet/CSV import health, and columnar storage efficiency metrics. Read this skill before any DuckDB operations.
connection_type	duckdb
preload	false

DuckDB Management Skill

Monitor, analyze, and optimize DuckDB instances safely.

MANDATORY: Discovery-First Pattern

Always check database metadata and list tables before any query operations. Never assume table names or column types.

Phase 1: Discovery

#!/bin/bash

DUCKDB_FILE="${DUCKDB_FILE:-my_database.duckdb}"

duck_query() {
    duckdb "$DUCKDB_FILE" -c "$1" 2>/dev/null
}

echo "=== DuckDB Version ==="
duckdb -c "SELECT version();" 2>/dev/null

echo ""
echo "=== Database Info ==="
duck_query "CALL pragma_database_size();"

echo ""
echo "=== Schemas ==="
duck_query "SELECT schema_name FROM information_schema.schemata;"

echo ""
echo "=== Tables ==="
duck_query "SELECT table_schema, table_name, table_type FROM information_schema.tables WHERE table_schema NOT IN ('pg_catalog','information_schema') ORDER BY table_schema, table_name;"

echo ""
echo "=== Extensions ==="
duck_query "SELECT extension_name, installed, loaded FROM duckdb_extensions() ORDER BY installed DESC, extension_name;"

echo ""
echo "=== Settings (key) ==="
duck_query "SELECT name, value FROM duckdb_settings() WHERE name IN ('memory_limit','threads','default_order','access_mode','temp_directory');"

Phase 1 outputs: Version, database size, table inventory, installed extensions, key settings.

Phase 2: Analysis

#!/bin/bash

DUCKDB_FILE="${DUCKDB_FILE:-my_database.duckdb}"
TABLE="${1:-my_table}"

duck_query() {
    duckdb "$DUCKDB_FILE" -c "$1" 2>/dev/null
}

echo "=== Table Details ==="
duck_query "DESCRIBE $TABLE;"

echo ""
echo "=== Table Statistics ==="
duck_query "SELECT COUNT(*) as row_count FROM $TABLE;"
duck_query "CALL pragma_storage_info('$TABLE');" | head -20

echo ""
echo "=== Column Stats ==="
duck_query "SELECT column_name, column_type, null_percentage, avg_width, n_unique FROM pragma_table_info('$TABLE');" 2>/dev/null || \
    duck_query "SELECT column_name, data_type, is_nullable FROM information_schema.columns WHERE table_name='$TABLE';"

echo ""
echo "=== Memory Usage ==="
duck_query "SELECT * FROM pragma_database_size();"

echo ""
echo "=== Recent Queries Profile ==="
duck_query "SELECT * FROM pragma_last_profiling_output;" 2>/dev/null || echo "Profiling not enabled"

echo ""
echo "=== Storage Info ==="
 -lh  2>/dev/null
 -lh  2>/dev/null ||  

Output Format

DUCKDB ANALYSIS
===============
Version: [version] | File: [path] | Size: [size]
Tables: [count] | Extensions: [loaded]

ISSUES FOUND:
- [issue with affected table/setting]

RECOMMENDATIONS:
- [actionable recommendation]

Anti-Hallucination Rules

1. NEVER assume resource names — always discover via CLI/API in Phase 1 before referencing in Phase 2.
2. NEVER fabricate metric names or dimensions — verify against the service documentation or --help output.
3. NEVER mix CLI commands between service versions — confirm which version/API you are targeting.
4. ALWAYS use the discovery → verify → analyze chain — every resource referenced must have been discovered first.
5. ALWAYS handle empty results gracefully — an empty response is valid data, not an error to retry.

Counter-Rationalizations

Shortcut	Counter	Why
"I'll skip discovery and check known resources"	Always run Phase 1 discovery first	Resource names change, new resources appear — assumed names cause errors
"The user only asked for a quick check"	Follow the full discovery → analysis flow	Quick checks miss critical issues; structured analysis catches silent failures
"Default configuration is probably fine"	Audit configuration explicitly	Defaults often leave logging, security, and optimization features disabled
"Metrics aren't needed for this"	Always check relevant metrics when available	API/CLI responses show current state; metrics reveal trends and intermittent issues
"I don't have access to that"	Try the command and report the actual error	Assumed permission failures prevent useful investigation; actual errors are informative