JPS6074836A - Data transfer system - Google Patents

Abstract

PURPOSE:To attain the bidirectional transfer of data and to reduce the overhead in order to improve the efficiency of a data transfer system, by transferring a dummy message to the node of the remote side from a corresponding node via a circuit in case no transfer data exists to enter the data in the wait state. CONSTITUTION:When no data to be transmitted to a node A from a node B exists, a control part 5 of the node B sends a dummy message D for synchronization to the node A. The message D is sent to the node B in the same way as long as the node A is not waiting for data. Then a data waiting mode is set. In case data are supplied simultaneously to both nodes in a waiting mode, the data are transferred, from the node having higher priority, then from the node having lower priority.

Description

Detailed Description of the Invention (a) Technical Field of the Invention The present invention relates to a data transfer system, and particularly relates to a data transfer system in which a data transfer mode is devised when two nodes are connected by a single communication line. .

(0) Background of the Technology When the database of a computer system is centralized, it is sufficient to send and receive data between the database and the host computer, but in a computer system where the database is distributed, the host computer There arises a need to transmit and receive data between the host computer and other host computers connected to it via a communication line.

In such cases, it is desirable to be able to efficiently transfer data via a communication line with as little overhead on the host computer as possible, and there is a need for the development of technical means that can meet such demands.

(c) Purpose of the Invention The present invention was devised focusing on the above-mentioned technical problem, and its purpose is to efficiently transfer data between nodes each having data to be transferred by minimizing overhead. The purpose of this invention is to provide a data transfer method that can be carried out efficiently.

Structure of the Invention In order to achieve this objective, the method of the present invention transmits a dummy message to the node when there is no data to be transferred between two nodes connected via a single communication line. However, the dummy message is transferred to the other node via the communication line, and the data is waited for when the dummy message is sent back and forth between the nodes.

Embodiments of the Invention The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows a detailed diagram of each node of the embodiment. This embodiment is implemented, for example, in a computer system with a distributed database.

In the figure, A and B are nodes, and C is a communication line connecting these nodes. Node A.

The details of B are shown in Figure 2 from a data source (not shown).
data input section l connected to the user), data input section 1
This data transfer device consists of a data storage section 2 connected to the data storage section 2, and a data transfer section 3 connected to the data storage section 2.In a computer system in which the database is distributed, this device is connected to the data transfer section of the host computer. It is equivalent. The data transfer section 3 is composed of a transmitting/receiving buffer 4 interposed between the data storage section 2 and the communication line C, and a control section 5 connected to the buffer 4 and the data storage section 2.

Next, a data transfer mode in the above configuration will be explained.

For convenience of explanation, node A has three data A1+A2 r
There is A3 and node B has two data Bl.

Assume that there is B2 (see Figure 3). These data are temporarily stored in the data storage section 2 via the data input section 1 from the user of each node in order to be transferred to the other node, and are transferred under the control of the control section 5 as follows.

First, node A sends data A1 to node B.

When node B receives the data, it sends data B1 to node A. Thereafter, data is transferred alternately in the order of data A2 + 82 + A3 using the same procedure. When data A8 is sent to node B,
Since node B has no more data to send to node A, a dummy message D for synchronization is sent to node A under the control of the control unit 5 of node B. When node A receives dummy message D, it knows that both nodes have no data, so node A sends dummy message D to node B and waits for data in the same manner as described above. Also, the node B that received the dummy message D is also waiting for data at that time.

In this state where both nodes are waiting for data, for example, two data AI + A2 are input to node A, but no data is input to node B, and data transfer is resumed. Assume that a situation occurs (see FIG. 4), in which case node A first sends data A1 to node B. Since node B has no data, a dummy message D is sent from node B to node A.
send. Similarly, node A sends data A2 to node B.
and node B sends a dummy message D to node A. At this point, node A has no more data, so node A sends a dummy message D to node B. In this way, both nodes wait for data.

Also, when both nodes are waiting for data,
If data is input to both nodes at the same time, a collision occurs because data is transferred at the same time. In this case, according to the priorities of both nodes, data is first transferred from the node with the higher priority, and then data is transferred from the node with the lower priority. This control is performed by the control section 5, but the control technique itself is well known and the details thereof will be omitted.

Although the above embodiment has been described between two nodes, the present invention can be applied between three or more nodes even when other nodes intervene between the two nodes.

(F) Effects of the Invention As described above, according to the present invention, 1) data can be transferred in both directions in an alternating manner via a single communication line; 2) messages are exchanged only when necessary; Effects such as overhead can be minimized and efficient data transfer can be achieved are obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a detailed diagram of each node in the embodiment of FIG. 1, FIG. 3 is a diagram showing an example of normal data transfer in the method of the present invention, and FIG. is a diagram showing an example of a case where two nodes restart data transfer after waiting for data. In the figure, A and B are nodes, C is a communication line, 1 is a data input section, 2 is a data storage section, 3 is a data transfer section, 4 is a transmission/reception buffer, and 5 is a control section. Figure 1 Figure 2 Figure 3 At, A2+A3 F5t 1e)z Waiting for data Waiting for D-5 Figure 4 Data generated at node A AI, Az D, -111-

Claims (2)

[Claims] (1) When data is transferred between two nodes connected via a single communication line, when there is no data to be transferred to the node, a dummy message is transferred from the node to the other node via the communication line, and a dummy message is sent. A data transfer method characterized by waiting for data when the data is sent back and forth between the nodes. (2) The data transfer method according to claim 1, wherein the node is a host computer of a computer system in which the database is distributed.