Duckdb

Query Lite's DuckDB Database

Safely query the PerformanceMonitor Lite DuckDB database using Python. This skill exists because DuckDB only allows one read-write connection at a time. When Lite is running (collecting data), it holds the write connection. External readers MUST connect in read-only mode.

Database Location

Since the #1832 fix (data moved OUT of Velopack's install root, which Setup.exe deletes), the store lives at:

%LOCALAPPDATA%\PerformanceMonitorLite-Data\monitor.duckdb

Builds from BEFORE that fix (3.3.0 and earlier) keep it at the old path, and the file only moves when a fixed build first runs:

%LOCALAPPDATA%\PerformanceMonitorLite\monitor.duckdb

Check the -Data path first; fall back to the old path if it does not exist.

How to Query (ALWAYS use this pattern)

Use Python with the duckdb module. ALWAYS connect in read-only mode.

python -c "
import duckdb, os
la = os.environ['LOCALAPPDATA']
p = la + '/PerformanceMonitorLite-Data/monitor.duckdb'
if not os.path.exists(p):
    p = la + '/PerformanceMonitorLite/monitor.duckdb'
con = duckdb.connect(p, read_only=True)
result = con.execute('YOUR SQL HERE').fetchall()
for row in result:
    print(row)
con.close()
"

CRITICAL RULES

1. ALWAYS use read_only=True -- without this, the connection will be blocked by Lite's write lock and hang or fail
2. NEVER use duckdb.connect() without read_only=True -- the default is read-write which WILL conflict with the running app
3. Use forward slashes in the path (Python on Windows handles this fine)
4. Close the connection when done -- don't leave read locks dangling
5. Use Python -- duckdb 1.4.4 is installed

Common Queries

List all tables:

SELECT table_name FROM information_schema.tables WHERE table_schema = 'main' ORDER BY table_name;

List columns for a table:

SELECT column_name, data_type FROM information_schema.columns WHERE table_name = 'TABLE_NAME' ORDER BY ordinal_position;

List all views:

SELECT table_name FROM information_schema.tables WHERE table_type = 'VIEW' ORDER BY table_name;

Row counts:

SELECT table_name, estimated_size FROM duckdb_tables() ORDER BY estimated_size DESC;

DuckDB vs SQL Server Syntax Notes

• String concatenation: || (not +)
• ILIKE for case-insensitive LIKE
• EPOCH_MS(timestamp_col) to convert to epoch
• strftime('%Y-%m-%d %H:%M:%S', ts) for formatting
• No TOP N -- use LIMIT N instead
• EXCLUDE clause: SELECT * EXCLUDE (col1, col2) FROM table