PostgreSQL

34.7. The Fast-Path Interface
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34.7. The Fast-Path Interface

PostgreSQL provides a fast-path interface to send simple function calls to the server.

Tip

This interface is somewhat obsolete, as one can achieve similar performance and greater functionality by setting up a prepared statement to define the function call. Then, executing the statement with binary transmission of parameters and results substitutes for a fast-path function call.

The function PQfn requests execution of a server function via the fast-path interface:

PGresult *PQfn(PGconn *conn,
               int fnid,
               int *result_buf,
               int *result_len,
               int result_is_int,
               const PQArgBlock *args,
               int nargs);

typedef struct
{
    int len;
    int isint;
    union
    {
        int *ptr;
        int integer;
    } u;
} PQArgBlock;

The `fnid argument is the OID of the function to be executed. args and nargs define the parameters to be passed to the function; they must match the declared function argument list. When the isint field of a parameter structure is true, the u.integer value is sent to the server as an integer of the indicated length (this must be 2 or 4 bytes); proper byte-swapping occurs. When isint is false, the indicated number of bytes at *u.ptr are sent with no processing; the data must be in the format expected by the server for binary transmission of the function’s argument data type. (The declaration of u.ptr as being of type `int * is historical; it would be better to consider it void *.) `result_buf points to the buffer in which to place the function’s return value. The caller must have allocated sufficient space to store the return value. (There is no check!) The actual result length in bytes will be returned in the integer pointed to by result_len. If a 2- or 4-byte integer result is expected, set result_is_int to 1, otherwise set it to 0. Setting result_is_int to 1 causes libpq to byte-swap the value if necessary, so that it is delivered as a proper `int value for the client machine; note that a 4-byte integer is delivered into `*result_buf for either allowed result size. When result_is_int is 0, the binary-format byte string sent by the server is returned unmodified. (In this case it’s better to consider result_buf as being of type `void *.)

PQfn always returns a valid PGresult pointer, with status PGRES_COMMAND_OK for success or PGRES_FATAL_ERROR if some problem was encountered. The result status should be checked before the result is used. The caller is responsible for freeing the PGresult with PQclear when it is no longer needed.

To pass a NULL argument to the function, set the `len field of that parameter structure to `-1; the `isint and u` fields are then irrelevant. (But this works only in protocol 3.0 and later connections.)

If the function returns NULL, `*result_len is set to `-1, and `*result_buf is not modified. (This works only in protocol 3.0 and later connections; in protocol 2.0, neither *result_len nor *result_buf` are modified.)

Note that it is not possible to handle set-valued results when using this interface. Also, the function must be a plain function, not an aggregate, window function, or procedure.

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34.6. Canceling Queries in Progress	Home	34.8. Asynchronous Notification

34.6. Canceling Queries in Progress

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34.8. Asynchronous Notification