JP6260361B2 - Data transfer system and method - Google Patents

Description

  The present invention relates to replication.

  A provider (for example, a telecommunications carrier) that provides a service by an information processing system implements a function of performing replication in the information processing system as part of a business continuity planning (BCP). In particular, replication is performed in a virtual environment from the viewpoint of reducing CAPEX (Capital Expenditure).

  Replication refers to generating a copy of a database managed in the information processing system on a computer different from the computer where the database is located. Since the tolerance to failures can be increased by replication, for example, the stop of the information processing system in the event of a disaster, etc. is suppressed, and even if the information processing system stops, it is recovered early and the provision of services is resumed Can do.

  When a copy is generated on another computer, the data is transmitted from the computer that manages the original data to the computer that manages the copy. However, packet loss occurs on the communication path between the computers, and the data Some may be lost. Particularly in a virtualized environment, a packet loss is likely to occur because a packet passes through a multistage network (for example, a virtual network, a LAN (Local Area Network), a WAN (Wide Area Network), etc.).

  As a countermeasure against data loss, a computer that manages original data retransmits data to a computer that manages replication by some method. In a data synchronization system in which a server and a client are provided in a certain document, a global unique identifier (GUID) corresponding to the update of the data item is prepared separately from the data item to be updated, and synchronization is performed using the GUID. It deals with dealing with the interruption of processing. However, the system in this document is based on the premise that the data item is updated in both the server and the client.

  TCP (Transmission Control Protocol) is provided with a retransmission mechanism. In TCP, the delivery of data is confirmed by an ACK (ie an acknowledgment). The computer that manages the original data retransmits the data when no ACK is received even after a predetermined time has elapsed (that is, when a time-out occurs). Here, the time until timeout is set to a longer time each time a timeout occurs. Therefore, when the delivery confirmation in TCP is used, the time for holding the communication buffer used for retransmission in the memory becomes long, which affects the processing by the application program. Therefore, it is not an appropriate technique in that the amount of resources (for example, memory) used for data retransmission increases.

Special table 2009-516273

  Accordingly, an object of the present invention, in one aspect, is to provide a technique for reducing the amount of resources used for data retransmission in a replication system.

  The data transfer system according to the present invention includes a first information processing device and a second information processing device. The first information processing apparatus described above sends the updated value of the first item among the plurality of items managed by the first information processing apparatus and the serial number indicating the update order to the second information processing apparatus. A transmission unit for transmission, a number storage unit for storing the serial number in association with the item identification information, and a serial number corresponding to the identification information for the first item stored in the number storage unit are transmitted together with the value of the first item. When the serial number sent to the second information processing device is sent back from the second information processing device, the setting unit for setting the serial number is deleted from the number storage unit, and a serial number smaller than the serial number is set. And a detection unit that detects from the number storage unit. And the transmission part described above transmits the value of the 2nd item already transmitted with the serial number detected by the detection part to a 2nd information processing apparatus again.

  In one aspect, in a replication system, the amount of resources used for data retransmission can be reduced.

FIG. 1 is a diagram showing a system outline of the present embodiment. FIG. 2 is a functional block diagram of a VM executed as an active server and a VM executed as a standby server. FIG. 3 is a diagram illustrating an example of data stored in the session data table. FIG. 4 is a diagram illustrating an example of data stored in the management table. FIG. 5 is a processing flow of processing executed when the session data is updated. FIG. 6 is a diagram illustrating an example of the update notification. FIG. 7 is a diagram illustrating an example of a packet including a sequence number. FIG. 8 is a processing flow of processing executed when retransmitting session data. FIG. 9 is a diagram for explaining storage and deletion of sequence numbers. FIG. 10 is a diagram for explaining storage and deletion of sequence numbers. FIG. 11 is a diagram for explaining storage and deletion of sequence numbers. FIG. 12 is a diagram for explaining storage and deletion of sequence numbers. FIG. 13 is a diagram for explaining storage and deletion of sequence numbers. FIG. 14 is a diagram for explaining storage and deletion of sequence numbers. FIG. 15 is a diagram for explaining the storage and deletion of sequence numbers. FIG. 16 is a diagram for explaining storage and deletion of sequence numbers. FIG. 17 is a functional block diagram of a computer.

  FIG. 1 shows a system overview in the present embodiment. For example, a network device 13 at the base 10 and a network device 23 at the base 20 are connected to the WAN 3 that is the Internet. The network device 13 is connected to the physical servers 11 and 12 and other network devices (not shown) via the LAN 14.

  The physical server 11 has a NIC (Network Interface Card) 112. In the physical server 11, a plurality of VMs (Virtual Machines) 111 are executed, and communication between the plurality of VMs 111 is performed via the virtual network 110. When the VM 111 communicates with a device other than the physical server 11, the VM 111 transmits session data to the network device 13 via the NIC 112. The network device 13 relays the session data received from the physical server 11 to another device. The base 20 is the same as the base 10 and will not be described.

  User terminals 51 and 52 are connected to the WAN 3 via the LAN 5. The user terminals 51 and 52 use a service provided by the VM at the base.

  In the following, it is assumed that one of the plurality of VMs 111 is executed as an active server, and one of the plurality of VMs 211 is executed as a standby server. The user terminals 51 and 52 use services provided by the VM 111 that is an active server. FIG. 2 shows a functional block diagram of the VM 111 and VM 211 in such a case. In the example of FIG. 2, the VM 111 that is an active server includes a reception unit 1110, a detection unit 1111, a management table storage unit 1112, a generation unit 1113, a transmission unit 1114, and a session data storage unit 1115.

  When the session data stored in the session data storage unit 1115 is updated, the generation unit 1113 generates a new sequence number generated by the generation unit 1113, which is a sequence number corresponding to the call ID and field number of the updated session data. Set to sequence number. Then, the generation unit 1113 outputs the generated sequence number to the transmission unit 1114. When the session data stored in the session data storage unit 1115 is updated, the transmission unit 1114 sends an update notification including the updated session data, call ID, field number, and generated sequence number to the standby system. It transmits to VM211 which is a server.

  The reception unit 1110 receives a sequence number from the VM 211 that is a standby server, and outputs the sequence number to the detection unit 1111. The detection unit 1111 deletes the sequence number received from the reception unit 1110 from the management table storage unit 1112. The detection unit 1111 detects a sequence number smaller than the sequence number received from the reception unit 1110 from the management table storage unit 1112. Then, the detection unit 1111 outputs the detected sequence number to the generation unit 1113. The generation unit 1113 updates the sequence number received from the detection unit 1111 with the new sequence number generated by the generation unit 1113. Then, the generation unit 1113 outputs the new sequence number and the call ID and field number corresponding to the new sequence number to the transmission unit 1114. The transmission unit 1114 reads session data corresponding to the call ID and field number received from the generation unit 1113 from the session data storage unit 1115. Then, the transmission unit 1114 retransmits the retransmission notification including the read session data, call ID, field number, and sequence number to the VM 211 that is the standby server.

  The VM 211 that is a standby server includes a reception unit 2110, a session data storage unit 2111, and a transmission unit 2112.

  The reception unit 2110 receives the update notification from the VM 111 that is the active server, and associates the session ID included in the update notification with the call ID and field number included in the update notification stored in the session data storage unit 2111. Store the data. In addition, the reception unit 2110 outputs the sequence number included in the update notification to the transmission unit 2112.

  The transmission unit 2112 transmits the sequence number received from the reception unit 2110 to the VM 111 that is an active server.

  FIG. 3 shows an example of a session data table stored in the session data storage units 1115 and 2111. In the example of FIG. 3, for each call ID, a field number and data stored in the field (in this embodiment, session data representing a call state) are stored. In the present embodiment, replication is performed from the session data storage unit 1115 to the session data storage unit 2111. Therefore, the session data storage unit 2111 stores a copy of the session data table stored in the session data storage unit 1115.

  FIG. 4 shows an example of a management table stored in the management table storage unit 1112. In the example of FIG. 4, a field number and a sequence number are stored for each call ID. The sequence number is a serial number indicating the update order.

  Next, processing performed when the session data is updated will be described with reference to FIGS.

  First, the generation unit 1113 detects that the session data stored in the session data storage unit 1115 has been updated by, for example, communication from the user terminal 51 or 52 (FIG. 5: Step S1). Also, the generation unit 1113 identifies the call ID and field number of the session data detected in step S1 from the session data table.

  The generation unit 1113 newly generates a sequence number (step S3). For example, if the last generated sequence number is “4”, the sequence number “5” is generated in step S3. The generation unit 1113 outputs the generated sequence number to the transmission unit 1114.

  The generation unit 1113 sets the sequence number corresponding to the call ID and field number of the updated session data in the management table to the sequence number generated in step S3 (step S5). In step S5, when the sequence number corresponding to the call ID and field number of the updated session data is stored in the management table, the sequence number is updated with the sequence number generated in step S3. On the other hand, if the sequence number corresponding to the call ID and field number of the updated session data is not stored in the management table, it is generated in step S3 in association with the call ID and field number of the updated session data. Stored sequence number. As a result, the sequence number generated at the time of the last update is stored in the management table.

  The generation unit 1113 outputs the call ID and field number of the updated session data to the transmission unit 1114. The transmission unit 1114 generates an update notification including the updated session data, the call ID and field number of the updated session data, and the sequence number generated in step S3, and transmits the update notification to the VM 211 that is the standby server ( Step S7).

  FIG. 6 shows an example of the update notification. In the example of FIG. 6, a header part and a data part are included. The header part includes a transmission source address, a destination address, and a sequence number. The data part includes a call ID, a field number, and data. A set of field numbers and data is included in the number of fields related to the update.

  The receiving unit 2110 of the VM 211 that is the standby server receives the update notification from the VM 111 that is the active server (step S9).

  The receiving unit 2110 updates the session data stored in the session data storage unit 2111 and corresponding to the call ID and field number included in the received update notification with the session data included in the received update notification (step S11). ). The reception unit 2110 outputs the sequence number included in the update notification to the transmission unit 2112.

  The transmission unit 2112 generates a packet including the sequence number received from the reception unit 2110, and sends it back to the VM 111 that is the active server (step S13).

  FIG. 7 shows an example of a packet including a sequence number. In the example of FIG. 7, a header part and a data part are included. The header part includes a transmission source address, a destination address, and a sequence number. The data portion includes other data.

  The receiving unit 1110 of the VM 111 that is the active server receives a packet including a sequence number from the VM 211 that is the standby server (step S15). The reception unit 1110 outputs the received sequence number to the detection unit 1111.

  The detection unit 1111 deletes the same sequence number as the sequence number received from the reception unit 1110 from the management table (step S17).

  The detecting unit 1111 searches the management table for a sequence number smaller than the sequence number received from the receiving unit 1110 (step S19).

  The sequence number smaller than the sequence number received from the reception unit 1110 is a sequence number that has not yet been sent back even though it is a sequence number transmitted to the VM 211 prior to the sequence number received from the reception unit 1110. Therefore, the update notification including this sequence number does not reach the VM 211 that is the standby server.

  Therefore, when a sequence number smaller than the sequence number received from the reception unit 1110 is detected in step S19, the following processing is performed to retransmit the session data.

  The process executed when retransmitting the session data will be described with reference to FIG. First, the detection unit 1111 outputs the sequence number detected in step S19 to the generation unit 1113. The generation unit 1113 updates the sequence number received from the detection unit 1111 stored in the management table with a new sequence number (FIG. 8: step S21). For example, when the last generated sequence number is “5”, the new sequence number in step S21 is set to “6”. The generation unit 1113 outputs the new sequence number and the call ID and field number corresponding to the new sequence number to the transmission unit 1114.

  The transmission unit 1114 reads the session data corresponding to the call ID and field number received from the generation unit 1113 from the session data table. Then, the transmission unit 1114 generates a retransmission notification including the call ID and field number received from the generation unit 1113, the session data corresponding to the call ID and field number, and the sequence number received from the generation unit 1113. Then, the transmission unit 1114 transmits a retransmission notification to the VM 211 that is a standby server (step S23). The structure of the retransmission notification is the same as the structure of the update notification shown in FIG.

  The receiving unit 2110 of the VM 211 that is the standby server receives a retransmission notification from the VM 111 that is the active server (step S25).

  The reception unit 2111 stores the session data included in the received retransmission notification in the session data table in association with the call ID and field number included in the received retransmission notification stored in the session data storage unit 2111 ( Step S27). Receiving section 2110 outputs the sequence number included in the retransmission notification to transmitting section 2112.

  The transmission unit 2112 generates a packet including the sequence number received from the reception unit 2110, and sends it back to the VM 111 that is the active server (step S29).

  The receiving unit 1110 of the VM 111 that is the active server receives a packet including a sequence number from the VM 211 that is the standby server (step S31). The reception unit 1110 outputs the received sequence number to the detection unit 1111.

  The detecting unit 1111 deletes the same sequence number as the sequence number received from the receiving unit 1110 from the management table (step S33).

  The detecting unit 1111 searches the management table for a sequence number smaller than the sequence number received from the receiving unit 1110 (step S35).

  In the system as shown in FIG. 1, when communication is performed between the VM 111 and the VM 211, the packet loss is likely to occur because the virtual network 110, the LAN 14, and the WAN 3 are used. In such a case, if delivery confirmation by ACK is used, a period for holding the communication buffer for retransmission becomes longer, which affects processing by the application program. However, in the present embodiment, updated session data is sequentially transmitted without waiting for reception of ACK. Therefore, it is not necessary to hold a communication buffer for retransmission, so that the amount of memory used can be reduced.

  In addition, transmission of session data (here, SD1) in a certain field has failed and SD1 is updated before the SD1 is retransmitted, and transmission of updated session data (here, SD2) is performed. Is successful. In such a case, it is not necessary to perform retransmission, so that it is possible to save memory resources and communication bandwidth used for retransmission.

  In addition, although the session data reaches the VM 211 that is the standby server, a packet including the sequence number may be lost during communication. In the present embodiment, such a case is treated as a session data transmission failure, so that the session data is retransmitted.

  The deletion and storage of the sequence number in the management table will be specifically described with reference to FIGS. Assume that data as shown in FIG. 9 is stored in the management table as an initial state. That is, the sequence number “1” is stored in association with each field number of the call ID “01”.

  In the state shown in FIG. 9, it is assumed that a packet including the sequence number “1” is received from the VM 211 that is a standby server. This means that the VM 211 that is the standby server has received the session data transmitted together with the sequence number “1”. In such a case, all sequence numbers “1” in the management table are deleted, and the management table is in a state as shown in FIG.

  In the state shown in FIG. 10, it is assumed that the session data of the fields having field numbers “3” and “4” are updated simultaneously. In this case, the sequence number “2” is stored in association with the field numbers “3” and “4” in the management table, and the management table is in a state as shown in FIG. The sequence number “2” is transmitted to the VM 211 that is the standby server together with the updated session data.

  Then, it is assumed that a packet including the sequence number “2” is received from the VM 211 that is a standby server. This means that the VM 211 which is the standby server has received the session data transmitted together with the sequence number “2”. In such a case, the sequence number “2” corresponding to the field numbers “3” and “4” in the management table is deleted, and the management table is in a state as shown in FIG.

  In the state shown in FIG. 11, it is assumed that the session data of the fields with field numbers “4” and “5” are updated simultaneously. In this case, the sequence number “3” is stored in association with the field numbers “4” and “5” in the management table, and the management table is in a state as shown in FIG. The sequence number “2” corresponding to the field number “3” remains unchanged. The sequence number “3” is transmitted to the VM 211 that is the standby server together with the updated session data.

  Then, it is assumed that a packet including the sequence number “3” is received from the VM 211 that is a standby server. This means that the VM 211 as the standby server has received the session data transmitted with the sequence number “3”. In such a case, the sequence number “3” corresponding to the field numbers “4” and “5” in the management table is deleted, and the management table is in a state as shown in FIG.

  Here, “2” which is a sequence number smaller than the received sequence number “3” is detected. Then, the sequence number corresponding to the field number “3” is updated to “4” which is a new sequence number, and the management table is in a state as shown in FIG. The session data already transmitted to the VM 211 that is the standby server together with the sequence number “2” is transmitted again to the VM 211 that is the standby server together with the new sequence number.

  Then, it is assumed that a packet including the sequence number “4” is received from the VM 211 that is a standby server. This means that the VM 211 that is the standby server has received the session data transmitted together with the sequence number “4”. In such a case, the sequence number “4” corresponding to the field number “3” in the management table is deleted, and the management table is in a state as shown in FIG.

  Although one embodiment of the present invention has been described above, the present invention is not limited to this. For example, the functional block configurations of the VMs 111 and 211 described above may not match the actual program module configuration.

  Further, the configuration of each table described above is an example, and the configuration may not be as described above. Further, in the processing flow, the processing order can be changed if the processing result does not change. Further, it may be executed in parallel.

  Although the sequence number is used in the above, it is not limited to the sequence number. Other identifiers indicating the update order may be used.

  Note that the physical servers 11 and 21 described above are computer devices, and display a memory 2501, a CPU (Central Processing Unit) 2503, and a hard disk drive (HDD: Hard Disk Drive) 2505 as shown in FIG. A display control unit 2507 connected to the device 2509, a drive device 2513 for the removable disk 2511, an input device 2515, and a communication control unit 2517 for connecting to a network are connected by a bus 2519. An operating system (OS) and an application program for executing the processing in this embodiment are stored in the HDD 2505, and are read from the HDD 2505 to the memory 2501 when executed by the CPU 2503. The CPU 2503 controls the display control unit 2507, the communication control unit 2517, and the drive device 2513 according to the processing content of the application program, and performs a predetermined operation. Further, data in the middle of processing is mainly stored in the memory 2501, but may be stored in the HDD 2505. In the embodiment of the present invention, an application program for performing the above-described processing is stored in a computer-readable removable disk 2511 and distributed, and installed in the HDD 2505 from the drive device 2513. In some cases, the HDD 2505 may be installed via a network such as the Internet and the communication control unit 2517. Such a computer apparatus realizes various functions as described above by organically cooperating hardware such as the CPU 2503 and the memory 2501 described above and programs such as the OS and application programs. .

  The embodiment of the present invention described above is summarized as follows.

  The data transfer system according to the first aspect of the present embodiment includes (A) a first information processing apparatus and (B) a second information processing apparatus. The first information processing apparatus described above is (a1) the updated value of the first item (for example, the upper one) among the plurality of items (for example, the field described above) managed by the first information processing apparatus. (Data described in the above) and a serial number indicating the update order are transmitted to the second information processing apparatus, and (a2) the serial number is associated with item identification information (for example, the field number described above). (A3) a setting unit that sets a serial number corresponding to the identification information of the first item stored in the number storage unit to the serial number transmitted together with the value of the first item; A detection unit that, when a serial number transmitted to the second information processing apparatus is sent back from the second information processing apparatus, deletes the serial number from the number storage unit and detects a serial number smaller than the serial number from the number storage unit; Yes That. And the transmission part described above transmits again the value of the 2nd item already transmitted with the serial number detected by the detection part (a11) to a 2nd information processing apparatus.

  In this way, useless retransmissions can be suppressed, and the amount of communication buffer used can be reduced compared to the case of using delivery confirmation by TCP. Retransmission can be performed while reducing the amount of memory.

  The setting unit described above assigns a new serial number to the value of the second item (a31), and assigns the serial number corresponding to the identification information of the second item stored in the number storage unit to the new serial number. May be set. The transmitting unit described above may transmit a new serial number to the second information processing apparatus together with the value of (a12) the second item. In this way, the value of the item can be retransmitted in the same way as in normal transmission.

  Further, the second information processing apparatus described above (b1) when the second item value and the new serial number are received from the first information processing apparatus, the received new serial number is sent to the first information processing apparatus. You may have the 2nd transmission part which sends back. This makes it possible to notify the first information processing apparatus that the second information processing apparatus has received the retransmitted second item value.

  Further, the second information processing apparatus described above may be (b2) an information processing apparatus that manages duplication of values of a plurality of items. Duplication can be properly performed without losing the value of the item.

  Further, the values of the plurality of items described above may be values regarding the call state. It should be noted that the value regarding the call state is not limited, and may be another value having a feature that only the latest value can be transmitted.

  In the data transfer method according to the second aspect of the present embodiment, (C) the updated value of the first item among a plurality of items and the serial number indicating the order of update are transmitted to another computer ( D) The serial number corresponding to the identification information of the first item stored in the number storage unit that stores the serial number in association with the identification information of the item is set to the serial number transmitted together with the value of the first item, E) When a serial number transmitted to another computer is sent back from another computer, the serial number is deleted from the number storage unit, and a serial number smaller than the serial number is detected from the number storage unit, and (F) detection unit The process of transmitting again the value of the 2nd item already transmitted with the serial number detected by (2) to another computer.

  A program for causing a computer to perform the processing according to the above method can be created. The program can be a computer-readable storage medium such as a flexible disk, a CD-ROM, a magneto-optical disk, a semiconductor memory, a hard disk, or the like. It is stored in a storage device. The intermediate processing result is temporarily stored in a storage device such as a main memory.

  The following supplementary notes are further disclosed with respect to the embodiments including the above examples.

(Appendix 1)
A first information processing device;
A second information processing device;
Have
The first information processing apparatus
A transmission unit that transmits the updated value of the first item among a plurality of items managed by the first information processing device and a serial number indicating the order of update to the second information processing device;
A number storage unit for storing serial numbers in association with identification information of items;
A setting unit that sets the serial number corresponding to the identification information of the first item stored in the number storage unit to the serial number transmitted together with the value of the first item;
When the serial number transmitted to the second information processing apparatus is sent back from the second information processing apparatus, the serial number is deleted from the number storage unit, and a serial number smaller than the serial number is detected from the number storage unit. A detection unit;
Have
The transmitter is
The value of the second item already transmitted together with the serial number detected by the detection unit is transmitted again to the second information processing apparatus.
Data transfer system.

(Appendix 2)
The setting unit
A new serial number is assigned to the value of the second item, a serial number corresponding to the identification information of the second item stored in the number storage unit is set as the new serial number,
The transmitter is
The data transfer system according to claim 1, wherein the new serial number is transmitted to the second information processing apparatus together with the value of the second item.

(Appendix 3)
The second information processing apparatus
The second transmission unit according to claim 2, further comprising: a second transmission unit configured to send back the received new serial number to the first information processing apparatus when the value of the second item and the new serial number are received from the first information processing apparatus. Data transfer system.

(Appendix 4)
The data transfer system according to any one of supplementary notes 1 to 3, wherein the second information processing apparatus is an information processing apparatus that manages duplication of values of the plurality of items.

(Appendix 5)
The data transfer system according to any one of appendices 1 to 4, wherein the values of the plurality of items are values regarding a call state.

(Appendix 6)
The updated value of the first item among a plurality of items and the serial number indicating the update order are transmitted to another computer,
A serial number corresponding to the identification information of the first item stored in the number storage unit that stores the serial number in association with the identification information of the item is set to the serial number transmitted together with the value of the first item;
When the serial number transmitted to the other computer is sent back from the other computer, the serial number is deleted from the number storage unit, and a serial number smaller than the serial number is detected from the number storage unit,
Retransmitting the value of the second item already transmitted with the detected serial number to the other computer;
A data transfer method in which processing is executed by a computer.

10, 20 bases 11, 12, 21, 22 Physical servers 13, 23 Network equipment 14, 24 LAN
110,210 Virtual network 111,211 VM
112, 212 NIC 1110, 2110 Reception unit 1111 Detection unit 1112 Management table storage unit 1113 Generation unit 1114, 2112 Transmission unit 1115, 2111 Session data storage unit 3 WAN 5 LAN
51,52 User terminal

Claims (3)

A first information processing device;
A second information processing device;
Have
The first information processing apparatus
A value storage unit that stores values of each of the plurality of items managed by the first information processing apparatus;
A number storage unit for storing a serial number representing the update order in association with the identification information of the item;
If the value of the first item of the values stored in the value storage unit is updated, the passing and number of the first item of the serial number stored in the number storage unit, a new first A setting section to set the serial number of
A transmitter that transmits the updated value of the first item and the new first serial number to the second information processing apparatus;
When the new first serial number is sent back from the second information processing apparatus, the new first serial number is deleted from the number storage unit, and a serial number smaller than the new first serial number is A detection unit for detecting from the number storage unit;
Have
The setting unit
A second item corresponding to the serial number detected by the detection unit is specified from the number storage unit, a new second serial number is assigned to the value of the specified second item, and stored in the number storage unit The serial number of the second item among the serial numbers being set is set to the new second serial number;
The transmitter is
Reads the value of the second item from the value storage unit, the value of the second item read, and a second serial number the new, sends to the second information processing apparatus,
Data transfer system. The second information processing apparatus
A second transmitter that sends back the received new second serial number to the first information processing apparatus when the value of the second item and the new second serial number are received from the first information processing apparatus; The data transfer system according to claim 1 . When the value of the first item is updated among the values stored in the value storage unit that stores the values of the plurality of items, the serial number indicating the update order is stored in association with the item identification information. the passing and number of the first item of the serial number stored in the number storage unit, set a new first serial number,
Sending the updated value of the first item and the new first serial number to another computer;
When the new first serial number is sent back from the other computer, the new first serial number is deleted from the number storage unit, and a serial number smaller than the new first serial number is stored in the number. Detect from the
A second item corresponding to the detected serial number is specified from the number storage unit, a new second serial number is assigned to the value of the specified second item, and the serial number stored in the number storage unit The serial number of the second item is set to the new second serial number,
Reads the value of the second item from the value storage unit, the value of the second item read, and a second serial number the new, sends to the other computer,
A data transfer method in which processing is executed by a computer.

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