Data chunks represent a horizontal slice of a table. They hold a number of vectors, that can each hold up to the VECTOR_SIZE rows. The vector size can be obtained through the duckdb_vector_size function and is configurable, but is usually set to 2048.

Data chunks and vectors are what DuckDB uses natively to store and represent data. For this reason, the data chunk interface is the most efficient way of interfacing with DuckDB. Be aware, however, that correctly interfacing with DuckDB using the data chunk API does require knowledge of DuckDB's internal vector format.

Data chunks can be used in two manners:

• Reading Data: Data chunks can be obtained from query results using the duckdb_fetch_chunk method, or as input to a user-defined function. In this case, the vector methods can be used to read individual values.
• Writing Data: Data chunks can be created using duckdb_create_data_chunk. The data chunk can then be filled with values and used in duckdb_append_data_chunk to write data to the database.

The primary manner of interfacing with data chunks is by obtaining the internal vectors of the data chunk using the duckdb_data_chunk_get_vector method. Afterwards, the vector methods can be used to read from or write to the individual vectors.

API Reference Overview

duckdb_data_chunk duckdb_create_data_chunk(duckdb_logical_type *types, idx_t column_count);
void duckdb_destroy_data_chunk(duckdb_data_chunk *chunk);
void duckdb_data_chunk_reset(duckdb_data_chunk chunk);
idx_t duckdb_data_chunk_get_column_count(duckdb_data_chunk chunk);
duckdb_vector duckdb_data_chunk_get_vector(duckdb_data_chunk chunk, idx_t col_idx);
idx_t duckdb_data_chunk_get_size(duckdb_data_chunk chunk);
void duckdb_data_chunk_set_size(duckdb_data_chunk chunk, idx_t size);

duckdb_create_data_chunk

Creates an empty DataChunk with the specified set of types.

Note that the result must be destroyed with duckdb_destroy_data_chunk.

Syntax

duckdb_data_chunk duckdb_create_data_chunk(
  duckdb_logical_type *types,
  idx_t column_count
);

Parameters

• types

An array of types of the data chunk.

• column_count

The number of columns.

• returns

The data chunk.

duckdb_destroy_data_chunk

Destroys the data chunk and de-allocates all memory allocated for that chunk.

Syntax

void duckdb_destroy_data_chunk(
  duckdb_data_chunk *chunk
);

Parameters

• chunk

The data chunk to destroy.

duckdb_data_chunk_reset

Resets a data chunk, clearing the validity masks and setting the cardinality of the data chunk to 0.

Syntax

void duckdb_data_chunk_reset(
  duckdb_data_chunk chunk
);

Parameters

• chunk

The data chunk to reset.

duckdb_data_chunk_get_column_count

Retrieves the number of columns in a data chunk.

Syntax

idx_t duckdb_data_chunk_get_column_count(
  duckdb_data_chunk chunk
);

Parameters

• chunk

The data chunk to get the data from

• returns

The number of columns in the data chunk

duckdb_data_chunk_get_vector

Retrieves the vector at the specified column index in the data chunk.

The pointer to the vector is valid for as long as the chunk is alive. It does NOT need to be destroyed.

Syntax

duckdb_vector duckdb_data_chunk_get_vector(
  duckdb_data_chunk chunk,
  idx_t col_idx
);

Parameters

• chunk

The data chunk to get the data from

• returns

The vector

duckdb_data_chunk_get_size

Retrieves the current number of tuples in a data chunk.

Syntax

idx_t duckdb_data_chunk_get_size(
  duckdb_data_chunk chunk
);

Parameters

• chunk

The data chunk to get the data from

• returns

The number of tuples in the data chunk

duckdb_data_chunk_set_size

Sets the current number of tuples in a data chunk.

Syntax

void duckdb_data_chunk_set_size(
  duckdb_data_chunk chunk,
  idx_t size
);

Parameters

• chunk

The data chunk to set the size in

• size

The number of tuples in the data chunk