Function REMOTE_compute_batch_size

src/remote/remote.cpp:175–251

USHORT REMOTE_compute_batch_size(rem_port* port,
								 USHORT buffer_used, P_OP op_code,
								 const rem_fmt* format)
{
/**************************************
 *
 *	R E M O T E _ c o m p u t e _ b a t c h _ s i z e
 *
 **************************************
 *
 * Functional description
 *
 * When batches of records are returned, they are returned as
 *    follows:
 *     <op_fetch_response> <data_record 1>
 *     <op_fetch_response> <data_record 2>
 * 	...
 *     <op_fetch_response> <data_record n-1>
 *     <op_fetch_response> <data_record n>
 *
 * end-of-batch is indicated by setting p_sqldata_messages to
 * 0 in the op_fetch_response.  End of cursor is indicated
 * by setting p_sqldata_status to a non-zero value.  Note
 * that a fetch CAN be attempted after end of cursor, this
 * is sent to the server for the server to return the appropriate
 * error code.
 *
 * Each data block has one overhead packet
 * to indicate the data is present.
 *
 * (See also op_send in receive_msg() - which is a kissing cousin
 *  to this routine)
 *
 * Here we make a guess for the optimal number of records to
 * send in each batch.  This is important as we wait for the
 * whole batch to be received before we return the first item
 * to the client program.  How many are cached on the client also
 * impacts client-side memory utilization.
 *
 * We optimize the number by how many can fit into a packet.
 * The client calculates this number (n from the list above)
 * and sends it to the server.
 *
 * The data size is either the XDR data representation, or the
 * actual message size (rounded up) if this is a symmetric
 * architecture connection.
 *
 **************************************/

	const USHORT op_overhead = (USHORT) xdr_protocol_overhead(op_code);

#ifdef DEBUG
	fprintf(stderr,
			   "port_buff_size = %d fmt_net_length = %d fmt_length = %d overhead = %d\n",
			   port->port_buff_size, format->fmt_net_length,
			   format->fmt_length, op_overhead);
#endif