Black Hole коннектор#

Примечание

Ниже приведена оригинальная документация Trino. Скоро мы ее переведем на русский язык и дополним полезными примерами.

Primarily Black Hole connector is designed for high performance testing of other components. It works like the /dev/null device on Unix-like operating systems for data writing and like /dev/null or /dev/zero for data reading. However, it also has some other features that allow testing Trino in a more controlled manner. Metadata for any tables created via this connector is kept in memory on the coordinator and discarded when Trino restarts. Created tables are by default always empty, and any data written to them is ignored and data reads return no rows.

During table creation, a desired rows number can be specified. In such cases, writes behave in the same way, but reads always return the specified number of some constant rows. You shouldn’t rely on the content of such rows.

Конфигурация#

Create etc/catalog/example.properties to mount the blackhole connector as the example catalog, with the following contents:

connector.name=blackhole

Примеры#

Create a table using the blackhole connector:

CREATE TABLE example.test.nation AS
SELECT * from tpch.tiny.nation;

Insert data into a table in the blackhole connector:

INSERT INTO example.test.nation
SELECT * FROM tpch.tiny.nation;

Select from the blackhole connector:

SELECT count(*) FROM example.test.nation;

The above query always returns zero.

Create a table with a constant number of rows (500 * 1000 * 2000):

CREATE TABLE example.test.nation (
  nationkey BIGINT,
  name VARCHAR
)
WITH (
  split_count = 500,
  pages_per_split = 1000,
  rows_per_page = 2000
);

Now query it:

SELECT count(*) FROM example.test.nation;

The above query returns 1,000,000,000.

Length of variable length columns can be controlled using the field_length table property (default value is equal to 16):

CREATE TABLE example.test.nation (
  nationkey BIGINT,
  name VARCHAR
)
WITH (
  split_count = 500,
  pages_per_split = 1000,
  rows_per_page = 2000,
  field_length = 100
);

The consuming and producing rate can be slowed down using the page_processing_delay table property. Setting this property to 5s leads to a 5 second delay before consuming or producing a new page:

CREATE TABLE example.test.delay (
  dummy BIGINT
)
WITH (
  split_count = 1,
  pages_per_split = 1,
  rows_per_page = 1,
  page_processing_delay = '5s'
);

SQL support#

The connector provides globally available, read operation, and supports the following additional features:

Примечание

The connector discards all written data. While read operations are supported, they return rows with all NULL values, with the number of rows controlled via table properties.