Row Block Allocation

Row block allocation is required when a producer produces data using the fetch_block method or when the consumer uses the fetch_into method to retrieve data.

udf_utils.cxx contains sample code that illustrates how to allocate and deallocate a row block.

These relevant data structures in the extfnapiv4.h header file are used when allocating a row block:

typedef struct a_v4_extfn_column_data {
    a_sql_byte          *is_null;
    a_sql_byte          null_mask;
    a_sql_byte          null_value;

    void                *data;
    a_sql_uint32        *piece_len;
    size_t              max_piece_len;

    void                *blob_handle;
} a_v4_extfn_column_data;

typedef struct a_v4_extfn_row {
    a_sql_uint32                *row_status;
    a_v4_extfn_column_data      *column_data;
} a_v4_extfn_row;

typedef struct a_v4_extfn_row_block {
    a_sql_uint32                max_rows;
    a_sql_uint32                num_rows;
    a_v4_extfn_row              *row_data;
} a_v4_extfn_row_block;

When allocating a row block, the developer must decide how many rows the row block is capable of holding, how many columns each row has, and the number of bytes required for each of those columns.

For a row block of size m, where each row has n columns, the developer must allocate an array of m a_v4_extfn_row structures. For each row in this array, the developer must allocate n a_v4_extfn_column_data structures.

These tables outline allocation requirements for each member of the row block structures: