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Version: devel

DuckDB

Install dlt with DuckDB​

To install the dlt library with DuckDB dependencies, run:

pip install "dlt[duckdb]"

Setup guide​

1. Initialize a project with a pipeline that loads to DuckDB by running:

dlt init chess duckdb

2. Install the necessary dependencies for DuckDB by running:

pip install -r requirements.txt

3. Run the pipeline:

python3 chess_pipeline.py

Write disposition​

All write dispositions are supported.

Data loading​

dlt will load data using large INSERT VALUES statements by default. Loading is multithreaded (20 threads by default). If you are okay with installing pyarrow, we suggest switching to Parquet as the file format. Loading is faster (and also multithreaded).

Data types​

duckdb supports various timestamp types. These can be configured using the column flags timezone and precision in the dlt.resource decorator or the pipeline.run method.

  • Precision: Supported precision values are 0, 3, 6, and 9 for fractional seconds. Note that timezone and precision cannot be used together; attempting to combine them will result in an error.
  • Timezone:
    • Setting timezone=False maps to TIMESTAMP.
    • Setting timezone=True (or omitting the flag, which defaults to True) maps to TIMESTAMP WITH TIME ZONE (TIMESTAMPTZ).

Example precision: TIMESTAMP_MS​

@dlt.resource(
    columns={"event_tstamp": {"data_type": "timestamp", "precision": 3}},
    primary_key="event_id",
)
def events():
    yield [{"event_id": 1, "event_tstamp": "2024-07-30T10:00:00.123"}]

pipeline = dlt.pipeline(destination="duckdb")
pipeline.run(events())

Example timezone: TIMESTAMP​

@dlt.resource(
    columns={"event_tstamp": {"data_type": "timestamp", "timezone": False}},
    primary_key="event_id",
)
def events():
    yield [{"event_id": 1, "event_tstamp": "2024-07-30T10:00:00.123+00:00"}]

pipeline = dlt.pipeline(destination="duckdb")
pipeline.run(events())

Names normalization​

dlt uses the standard snake_case naming convention to keep identical table and column identifiers across all destinations. If you want to use the duckdb wide range of characters (i.e., emojis) for table and column names, you can switch to the duck_case naming convention, which accepts almost any string as an identifier:

  • New line (\n), carriage return (\r), and double quotes (") are translated to an underscore (_).
  • Consecutive underscores (_) are translated to a single _

Switch the naming convention using config.toml:

[schema]
naming="duck_case"

or via the env variable SCHEMA__NAMING or directly in the code:

dlt.config["schema.naming"] = "duck_case"
caution

duckdb identifiers are case insensitive but display names preserve case. This may create name collisions if, for example, you load JSON with {"Column": 1, "column": 2} as it will map data to a single column.

Supported file formats​

You can configure the following file formats to load data into duckdb:

  • insert-values is used by default.
  • Parquet is supported.
    note

    duckdb cannot COPY many Parquet files to a single table from multiple threads. In this situation, dlt serializes the loads. Still, that may be faster than INSERT.

  • JSONL
tip

duckdb has timestamp types with resolutions from milliseconds to nanoseconds. However, only the microseconds resolution (the most commonly used) is time zone aware. dlt generates timestamps with timezones by default, so loading parquet files with default settings will fail (duckdb does not coerce tz-aware timestamps to naive timestamps). Disable the timezones by changing the dlt Parquet writer settings as follows:

DATA_WRITER__TIMESTAMP_TIMEZONE=""

to disable tz adjustments.

Supported column hints​

duckdb can create unique indexes for columns with unique hints. However, this feature is disabled by default as it can significantly slow down data loading.

Destination configuration​

By default, a DuckDB database will be created in the current working directory with a name <pipeline_name>.duckdb (chess.duckdb in the example above). After loading, it is available in read/write mode via with pipeline.sql_client() as con:, which is a wrapper over DuckDBPyConnection. See duckdb docs for details.

The duckdb credentials do not require any secret values. You are free to pass the credentials and configuration explicitly. For example:

# will load data to files/data.db (relative path) database file
p = dlt.pipeline(
  pipeline_name='chess',
  destination=dlt.destinations.duckdb("files/data.db"),
  dataset_name='chess_data',
  dev_mode=False
)

# will load data to /var/local/database.duckdb (absolute path)
p = dlt.pipeline(
  pipeline_name='chess',
  destination=dlt.destinations.duckdb("/var/local/database.duckdb"),
  dataset_name='chess_data',
  dev_mode=False
)

The destination accepts a duckdb connection instance via credentials, so you can also open a database connection yourself and pass it to dlt to use.

import duckdb

db = duckdb.connect()
p = dlt.pipeline(
  pipeline_name="chess",
  destination=dlt.destinations.duckdb(db),
  dataset_name="chess_data",
  dev_mode=False,
)

# Or if you would like to use an in-memory duckdb instance
db = duckdb.connect(":memory:")
p = pipeline_one = dlt.pipeline(
  pipeline_name="in_memory_pipeline",
  destination=dlt.destinations.duckdb(db),
  dataset_name="chess_data",
)

print(db.sql("DESCRIBE;"))

# Example output
# ┌──────────┬───────────────┬─────────────────────┬──────────────────────┬───────────────────────┬───────────┐
# │ database │    schema     │        name         │     column_names     │     column_types      │ temporary │
# │ varchar  │    varchar    │       varchar       │      varchar[]       │       varchar[]       │  boolean  │
# ├──────────┼───────────────┼─────────────────────┼──────────────────────┼───────────────────────┼───────────┤
# │ memory   │ chess_data    │ _dlt_loads          │ [load_id, schema_n…  │ [VARCHAR, VARCHAR, …  │ false     │
# │ memory   │ chess_data    │ _dlt_pipeline_state │ [version, engine_v…  │ [BIGINT, BIGINT, VA…  │ false     │
# │ memory   │ chess_data    │ _dlt_version        │ [version, engine_v…  │ [BIGINT, BIGINT, TI…  │ false     │
# │ memory   │ chess_data    │ my_table            │ [a, _dlt_load_id, …  │ [BIGINT, VARCHAR, V…  │ false     │
# └──────────┴───────────────┴─────────────────────┴──────────────────────┴───────────────────────┴───────────┘
note

Be careful! The in-memory instance of the database will be destroyed once your Python script exits.

This destination accepts database connection strings in the format used by duckdb-engine.

You can configure a DuckDB destination with secret / config values (e.g., using a secrets.toml file)

destination.duckdb.credentials="duckdb:///_storage/test_quack.duckdb"

The duckdb:// URL above creates a relative path to _storage/test_quack.duckdb. To define an absolute path, you need to specify four slashes, i.e., duckdb:////_storage/test_quack.duckdb.

Dlt supports a unique connection string that triggers specific behavior for the duckdb destination:

  • :pipeline: creates the database in the working directory of the pipeline, naming it quack.duckdb.

Please see the code snippets below showing how to use it:

  1. Via config.toml
destination.duckdb.credentials=":pipeline:"
  1. In Python code
p = pipeline_one = dlt.pipeline(
  pipeline_name="my_pipeline",
  destination=dlt.destinations.duckdb(":pipeline:"),
)

Additional configuration​

Unique indexes may be created during loading if the following config value is set:

[destination.duckdb]
create_indexes=true

dbt support​

This destination integrates with dbt via dbt-duckdb, which is a community-supported package. The duckdb database is shared with dbt. In rare cases, you may see information that the binary database format does not match the database format expected by dbt-duckdb. You can avoid this by updating the duckdb package in your dlt project with pip install -U.

Syncing of dlt state​

This destination fully supports dlt state sync.

Additional Setup guides​

This demo works on codespaces. Codespaces is a development environment available for free to anyone with a Github account. You'll be asked to fork the demo repository and from there the README guides you with further steps.
The demo uses the Continue VSCode extension.

Off to codespaces!

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