Configuration

DuckDB is configured at three levels: engine-wide (DBConfig), per-connection (ClientContext overrides), and per-session via PRAGMA/SET. The full list of settings is auto-generated from src/common/settings.json.

Looking up settings

SELECT * FROM duckdb_settings();              -- everything available
SELECT * FROM duckdb_settings() WHERE name LIKE '%memory%';
SELECT current_setting('threads');
PRAGMA threads;                               -- equivalent
SET threads = 4;                              -- override for this session
RESET threads;                                -- restore default

Some settings are global only (must be set on the DBConfig before opening), others are per-session. The scope column in duckdb_settings says which.

Frequently used settings

Setting	Default	What it controls
memory_limit	80% of system memory	Buffer manager budget. Spills when exceeded.
threads	number of CPUs	Worker pool size for TaskScheduler.
temp_directory	platform default	Where spill files go.
default_block_size	256 KB	Block size for new databases (immutable per database).
wal_autocheckpoint	16 MB	WAL size that triggers a checkpoint.
force_compression	empty	Force a specific compression codec; otherwise auto.
enable_progress_bar	off	CLI progress bars.
enable_profiling	off	none / query_tree / json.
profile_output	stdout	Path for the profile dump.
default_collation	empty	Default string collation (with the ICU extension).
TimeZone	system	Active time zone (with ICU).
IntervalStyle	postgres	postgres / iso_8601.
enable_object_cache	true	Reuse parsed parquet metadata across queries.
autoload_known_extensions	true	Auto-load extensions for known URIs / functions.
allow_unsigned_extensions	false	Permit unsigned .duckdb_extension files.
errors_as_json	false	Emit error data as JSON for structured logging.
disabled_optimizers	empty	Comma-separated optimizer-pass names to disable. Useful for debugging.
arrow_large_buffer_size	false	Force Arrow conversions to use 64-bit offsets.
enable_logging	false	Turn on the structured logger (see systems/main).
log_query_path	empty	If non-empty, append every executed query to the file.

The full list (~200 entries) lives in src/common/settings.json. Every entry has a corresponding setter/getter generated into src/main/settings/.

Pragmas

Some configuration is exposed only as PRAGMA (not SET):

Pragma	Effect
PRAGMA force_checkpoint;	Flush WAL into the database file now.
PRAGMA enable_progress_bar;	Enable the progress bar this session.
PRAGMA enable_object_cache;	Toggle the parsed-metadata cache.
PRAGMA threads = 4;	Synonym for SET threads = 4.
PRAGMA database_size;	Print database size info.
PRAGMA show_databases;	List attached databases.
PRAGMA show_tables;	List tables in the current schema.
PRAGMA show_tables_expanded;	Same plus columns.
PRAGMA functions;	List registered functions.
PRAGMA version;	DuckDB version + release date.
PRAGMA platform;	Compiled platform string.

Pragmas live in src/function/pragma/.

Configuration via the C API

duckdb_database db;
duckdb_config config;
duckdb_create_config(&config);
duckdb_set_config(config, "memory_limit", "4GB");
duckdb_set_config(config, "threads", "4");
duckdb_open_ext(":memory:", &db, config, NULL);
duckdb_destroy_config(&config);

Implementation: src/main/capi/config-c.cpp, config_options-c.cpp.

Per-connection overrides

ClientContext holds per-connection setting overrides. Connection::Query("SET threads=8") only affects the current connection. The C++ binding is Connection::SetConfig.

Storage settings (immutable)

A handful of settings are baked into the database file at creation and cannot be changed afterward:

Setting	Effect
default_block_size	Block size for the file.
default_string_encoding	UTF-8 vs ASCII.
encryption_key	If set, the database is encrypted on disk.

These are consumed by StorageManager during CREATE DATABASE (i.e., the first open of a new file).

Logging and observability

DuckDB ships a structured logger:

SET enable_logging = true;
SET log_query_path = '/tmp/queries.log';

The logger is implemented in src/logging/; its C interface is in src/main/capi/logging-c.cpp. See how-to-contribute/debugging.

Where to look

• src/common/settings.json — source of truth for settings.
• src/main/settings/ — generated setter/getter files.
• src/main/config.cpp — DBConfig implementation.
• scripts/generate_settings.py — generator.