JP5487420B2 - File duplication necessity determination method, communication apparatus, computer program, and peer-to-peer communication system - Google Patents

Description

  The present invention relates to a peer-to-peer communication system, and to a peer-to-peer file sharing network. In particular, it relates to smoothing of access frequency between peers.

  In an information communication system, a communication network form configured only from functionally equivalent communication devices (referred to as peers) is referred to as a peer-to-peer network. In such a network form, there is no special server that centralizes management of information exchanged between peers and peers.

  Among peer-to-peer networks, a network that shares a data unit such as a file (hereinafter collectively referred to as a file) between peers is called a peer-to-peer file sharing network. A file shared in this specification is called a shared file. In a peer-to-peer file sharing network, each peer is a client that uses a file and serves as a server that provides the file to each peer.

  In a peer-to-peer file sharing network, for example, Patent Document 1 and Non-Patent Document 1 describe a method of generating a copy of a file and arranging it on a plurality of peers in order to search a shared file at high speed and reliably. In this type of network, most of the shared files will have peers that are located closer to the network as compared to the case where the peer holding the file to be searched is alone. The search can be performed at high speed. In addition, because the search target file is located in multiple peers, the search request is more reliably propagated to the peer holding the search target file than when the single peer holds it. The Hereinafter, a method of arranging the same file on a plurality of peers in a peer-to-peer file sharing network will be referred to as a “multiple arrangement method”. By applying the replication arrangement method, fast and reliable search can be realized, and the search performance of the peer-to-peer file sharing network can be improved.

  In the copy placement method, the search performance varies depending on the number of copies of each file placed on the network and the selection of peers to be placed. In general, because the frequency of search targets varies from file to file, placing the same number of copies of shared files on the network places a higher load on peers with files that are searched more frequently than other peers. It is not preferable from the viewpoint of dispersion. Focusing on this point, Patent Document 2 and Non-Patent Document 2 describe a method of arranging the number of replicas according to the search frequency of the file.

  In addition, if the copy of the shared file is concentrated on a specific peer, the load of the peer becomes higher than that of other peers, which is not preferable from the viewpoint of load distribution. Techniques in view of this point are described in Non-Patent Document 2 and Non-Patent Document 3. These documents describe a method for distributing files so that the amount of file replication is not biased to specific nodes.

Japanese Patent Laying-Open No. 2005-227842 (FIG. 5) JP 2007-65714 A (paragraphs 0014 and 0022) Q. Lv, P.I. Cao, E .; Cohen, S.M. Li, K.K. Schenker, “Search and replication in unstructured peer-to-peer networks”, Proceedings of the 16th ACM international conference on Supercomputing, USA, 2002, June. 84-95 M.M. Uchida, K .; Ohnishi, and K.K. Ichikawa, "Dynamic storage load balancing with analogy to thermal diffusion for P2P file sharing", Proceedings from the 2006 workshop on Interdisciplinary systems approach in performance evaluation and design of computer & communications systems, 2006 years, p. 6 H. Yamamoto, D.H. Maruta, and Y.M. Oie, “Replication method for loading balancing on distributed storages in P2P networks,” IEICE Transactions on Information and Systems, January 2006.

  However, according to the conventional technique, it has not been possible to prevent the access load from being concentrated on the storage device of a specific peer in the network.

  According to Patent Document 1, a file copy is arranged to distribute the number of times the shared file is read. At that time, consideration is given to distributing the access load to the storage device accompanying the file copy arrangement. Absent. For example, when the number of times of reading the file F1 is large, the number of times of reading the file F1 at each of the arranged peers can be reduced by arranging the file F1 at a plurality of peers. However, there are cases where other files F2, F3,... With a large number of reads are arranged in the same peer, and it is not considered to distribute the access load on such peers.

  Further, Patent Document 2, Non-Patent Document 2, and Non-Patent Document 3 disclose techniques for distributing the amount of file duplication so that the storage device of a specific node is not biased. These technologies distribute the capacity used by storage devices among peers in the network, but generally the size of the file and the frequency of access to the file are irrelevant, and generally there is a large bias in the popularity of the file. In many cases, peers arranged with the same number of files often have a bias in access frequency to these peers. In other words, these prior arts do not consider smoothing the bias in access frequency between peers. For this reason, access may be concentrated on a peer having a storage device in which a frequently accessed file is arranged, and the access load cannot be distributed among the peers.

  Furthermore, in the conventional technology, the time change of the access frequency to the shared file is not taken into consideration. Usually, the access frequency for a certain shared file is not constant and changes with time. As a result, even if there is no change in the arranged file, the access frequency to the peer changes with time, and the distribution of the access frequency for each peer in the network also changes with time. However, according to the conventional technique, the response to such a change with time has not been considered.

  The present invention has been made in view of such circumstances, and the problem to be solved by the present invention is to reduce the access load even when sharing a file group in which a high access frequency and a low access frequency are shared. It is to provide a peer-to-peer file sharing network that is distributed among peers and responds to changes in access frequency over time.

  In order to solve the above-mentioned problem, the present invention provides a file duplication necessity determination method as one aspect thereof. That is, whether a peer of a peer-to-peer communication system that stores a copy of the same file in multiple peer storage devices replicates the file to keep the file to be transmitted to the other peer in the peer storage device. In the method for determining whether or not the reference information storage device of the peer stores the reference information related to the access made from the other peer to the peer during a predetermined period (S106 in FIG. 2); A step in which the peer processing device calculates an index value based on the reference information (S103), a step in which the peer processing device determines whether the file needs to be copied based on the index value (S104), and a determination The peer processing device updates the reference information stored in the reference information storage device according to the result (S106). To provide a determination method.

  According to another aspect of the present invention, there is provided a communication device functioning as a peer of a peer-to-peer communication system that stores a copy of the same file in a plurality of peer storage devices. Means for storing the reference information related to the access made to (see reference information storage device 43 in FIG. 1), means for calculating the index value based on the reference information (index value calculating unit 42), and based on the index value Means for determining whether the file needs to be copied (file copy control unit 41) and means for updating the reference information stored in the storage device (index value calculation unit 42) according to the determination result A communication device is provided.

  According to another aspect of the present invention, there is provided a computer program for causing a computer to function as a peer in a peer-to-peer communication system that stores a copy of the same file in a plurality of peer storage devices. Means for storing reference information relating to access made to the peer, means for calculating an index value based on the reference information, means for determining whether or not copying of the file is necessary based on the index value, and determination There is provided a computer program characterized by functioning as means for updating reference information stored in a storage device in accordance with the result of the above.

  Furthermore, the present invention provides, as another aspect, a recording medium that records the above-described computer program, a computer that includes this recording medium and that operates according to the computer program, and a peer-to-peer communication system that uses the above-described communication apparatus or computer as a peer. .

  According to the present invention, a peer with a high index value calculated from reference information related to access does not hold a file, but holds it with a low peer. As a result, when deciding which peer to place a shared file in a peer-to-peer communication network, it is not placed on a peer with a high index value, but is placed on a peer with a low index value. It can be smoothed with. Moreover, since it determines based on the index value in the latest period, even if the index value of each peer changes with progress of time, the change can be followed.

  A peer-to-peer communication system 100 according to an embodiment of the present invention will be described with reference to FIG. The peer-to-peer communication system 100 includes a plurality of communication devices 1 serving as peers and a communication network 6. In FIG. 1, only one communication device 1 is described as a peer for simplification, but it is assumed that many peers similar to the communication device 1 are actually connected to the communication network 6.

  The communication device 1 includes a search request unit 2, a file transfer unit 3, a file replication unit 4, and a file storage device 5. The search request unit 2 transmits / receives a search request to / from another peer via the communication network 6. The file transfer unit 3 transmits / receives a file shared in the peer-to-peer communication system 100 (hereinafter referred to as a shared file) to / from other peers via the communication network 6. The file duplicating unit 4 duplicates the shared file. The file storage device 5 stores the shared file.

  The communication apparatus 1 is an information processing apparatus that includes a network interface and operates according to a peer-to-peer file sharing program. The network interface device may be a so-called LAN card or a wireless communication network device for connecting to a mobile communication network such as a mobile phone network or a PHS network. Specifically, a personal computer, a workstation, a mobile phone, a PDA, or the like can be used as the information processing apparatus.

  The communication network 6 is a network that connects the communication devices 1 that are peers to each other. The communication network 6 is realized by, for example, a wired communication system such as Ethernet (registered trademark), a wireless communication system such as a wireless LAN, and an overlay network virtually configured on the communication system.

  The search request unit 2 includes a search request control unit 21, a search request reception unit 22, and a search request transmission unit 23. Each part will be described below.

  The search request control unit 21 controls the search request reception unit 22 and the search request transmission unit 23 to perform processing for transmitting and receiving a search request to and from other peers via the communication network 6. The search request is a request for determining whether or not a shared file to be searched is held.

  The search request receiving unit 22 performs a process of receiving a search request from another peer via the communication network 6 under the control of the search request control unit 21.

  The search request transmission unit 23 performs processing for transmitting a search request to another peer via the communication network 6 under the control of the search request control unit 21.

  The search request unit 2 operates as follows in cooperation with these units. When receiving a search request from another peer through the search request receiving unit 22, the search request control unit 21 determines whether or not the corresponding file is stored in the file storage device 5. When it is determined that the corresponding file is stored, the search request control unit 21 notifies the request source peer through the search request transmission unit 23 or transmits the corresponding file through the file transfer unit 3 to the request source communication. Send to device. On the other hand, if it is determined that the corresponding file is not stored in the file storage device 5, the search request control unit 21 transfers the search request to another communication device different from the request source through the search request transmission unit 23.

  The file transfer unit 3 includes a file transfer control unit 31, a transfer file reception unit 32, and a transfer file transmission unit 33. Each part will be described below.

  Based on the instruction from the search request control unit 2, the file transfer control unit 31 transmits the file stored in the file storage device 5 to another communication device through the transfer file transmission unit 33. In addition, a file received from another communication device through the transfer file receiving unit 32 is transferred to another communication device through the transfer file transmission unit 33, and the file is transferred to the file replication control unit 4.

  The transfer file receiving unit 32 receives a file from another communication device through the communication network 6.

  The transfer file transmission unit 33 transmits a file to another communication device through the communication network 6.

  The file replication unit 4 includes a file replication control unit 41, an index value calculation unit 42, and a reference information storage device 43. Each part will be described below.

  The file replication control unit 41 determines whether or not it is necessary to replicate the file, and stores the file in the file storage device 5 according to the determination result. When a file is received from the file transfer unit 3, it is determined whether to store the file based on the index value calculated by the index value calculation unit 42, that is, whether replication is necessary, and the file is determined according to the result. Is stored in the file storage device 5. The index value may simply determine whether the file is stored or not in a binary manner. In this case, the determination of necessity of copying follows the index value as it is. The index value may be a probability. In this case, the file duplication control unit 5 separately generates a random number, compares the index value and the random number, and determines whether or not duplication is necessary. For example, an index value is generated as a probability of 0 to 1 for storing the file based on the access load, and compared with a separately generated random number of 0 to 1, and if the random number is less than or equal to the index value, the file is stored If the random number exceeds the index value, the file may not be stored. In particular, when the copy history of the file in the communication device 1 is used as the reference information to be referred to when generating the index value, and when it is determined that the copy is to be made in the copy necessity determination, The control unit 41 updates the reference information held in the reference information storage unit 43 via the index value calculation unit 42.

  The index value calculation unit 42 calculates an index value based on the reference information stored in the reference information storage device 43 and notifies the file replication control unit 41 of the index value. As the reference information, values indicating the access load of the communication device 1 itself, the state of the other communication device, the access load, etc. can be considered, and an index value is generated by combining these values alone or in combination. Also good. In particular, when a file replication history in the communication device 1 is used as an index value, the index value calculation unit 42 refers to the reference information storage device 43 based on the file replication notification notified from the file replication control unit 41. The history information stored as information is updated.

  The reference information storage device 43 stores reference information. The reference information to be stored differs depending on the index value calculated by the index value calculation unit 42.

  The file storage device 5 stores a copy of the shared file for the purpose of distribution to other communication devices of the peer-to-peer communication system 100.

  Next, the operation of the peer-to-peer communication system 100 will be described. Communication devices 1a, 1b, and 1c (not shown) are communication devices that operate as peers of the peer-to-peer communication system 100 having the same configuration as that of the communication device 1. The communication device 1 is used as a reference symbol for each part of these communication devices. The reference numerals of the corresponding parts are appended with any of a, b, and c.

  When an instruction to search for the file F is input by a user operation or an application program, the search request transmission unit 22 of the communication device 1 responds to the search request for searching for the file F by peer-to-peer communication. It transmits with respect to the other communication apparatus 1a of the system 100. FIG. Here, it is assumed that the communication device 1a does not hold the file F and the communication device 1b holds the file F. In the communication device 1a, when the search request receiving unit 22a receives the search request, the search request control unit 21a determines whether or not the file F is held in the file storage device 5a. As described above, the communication device 1a does not hold the file F. At this time, the search request control unit 21a transfers the search request to the other communication device 1b in a bucket relay manner by the search request transmission unit 23a. The communication device 1b that has received the search request determines whether or not the file F exists in the file storage device 5b in the same manner as the communication device 1a. As described above, the communication device 1b holds the file F. At this time, the search request control unit 21b notifies the file transfer control unit 31b to that effect, and in response, the file transfer control unit 31b receives the file F from the file storage device 5b via the file replication control unit 41b. The file F is read and transferred from the transfer file transmission unit 33b to the communication device 1 that is the transmission source of the search request via the communication network 6. The present invention does not depend on the search request communication method, and may be a method in another general peer-to-peer network. Therefore, a more detailed description of the search request communication method is omitted.

  Here, the operation of the communication apparatus 1 will be described with reference to FIG. When the transfer file receiving unit 32 receives the file F from the communication device 1b (step S101), the file transfer control unit 31 determines whether it is necessary to transfer to another communication device according to a predetermined determination process. If necessary, the transfer file transmission unit 33 transmits the file F to the communication device 1c, for example (step S102), and passes the file F to the file duplication control unit 41. Upon receiving the file F, the file replication control unit 41 instructs the index value calculation unit 42 to calculate the index value. In response to this instruction, the index value calculation unit 41 is stored in the reference information storage device 43. An index value is calculated based on the reference information that is present (step S103). Further, the file duplication control unit 41 determines whether or not duplication is necessary based on the calculated index value (step S104). When the determination result for copying is obtained, the file copy control unit 41 stores the file F in the file storage device 5 for the purpose of distribution to other communication devices (step S105) and performs file copy. This is stored in the reference information storage device 43 via the index value calculation unit 42 (step S106). When the determination result indicating that the copy is not performed is obtained in the copy necessity determination, the process returns to step S101.

  A peer-to-peer communication system 200 according to the first embodiment will be described with reference to FIG. Here, differences from the peer-to-peer communication system 100 will be described.

  The communication device 1 is realized by an application on a personal computer connected to the Internet. With this application, a peer-to-peer file sharing network is configured as an overlay network on the Internet.

  The reference information storage device 43 stores history information as reference information. Here, the history information is information indicating whether or not a file received in a bucket relay manner from the other communication device is written in the file storage device 5 of the communication device 1 for each unit time within a predetermined period. . The unit time length is u, the predetermined period is represented by Nu, and N is called an average time width. I (t) = 1 represents that writing has been performed within a unit time that exceeds time t−u and is less than or equal to time t, and I (t) = 0 represents that writing has not been performed. When the current time is tc, the history information stored in the reference information storage device 43 is the presence / absence of writing I (tc−Nu + u), I (tc) at each time of time tc−Nu + u, tc−Nu + 2u,. -Nu + 2u), ..., I (tc). When the time advances, the reference information storage device 43 discards the oldest I (t) in the history information and stores a new I (t) instead.

  The index value calculation unit 42 calculates the access load L as an index value from the history information stored in the reference information storage device 43. Here, the access load L is the average value of I (t) within the period indicated by the average time width, and L = (1 / N) ΣI (t) = (1 / N) {I (tc−Nu + u) + I ( tc−Nu + 2u) +... + I (tc)}.

  The peer-to-peer communication system 200 includes an index value request transmission unit 71, an index value notification reception unit 72, an index value request reception unit 73, and an index value notification transmission unit 74 in addition to each unit of the peer-to-peer communication system 100. The index value request transmission unit 71 transmits an index value request to each peer that can communicate directly via the communication network 6, that is, to each adjacent peer. The index value request is a signal for notifying the received communication device of its own index value, that is, a signal for requesting to return an index value notification. The index value notification receiving unit 72 receives an index value notification from an adjacent peer. The index value request receiving unit 73 receives an index value request from an adjacent peer. The index value notification transmission unit 74 transmits an index value notification to the adjacent peer. In this embodiment, since the index value is the access load, the index value notification and the index value request transmitted / received to / from the neighboring peer are signals for notifying and requesting the access load.

  The file replication control unit 41 controls the index value request transmission unit 71, the index value notification reception unit 72, the index value request reception unit 73, and the index value notification transmission unit 74, and performs an index value request and index between adjacent peers. Send and receive value notifications. When the index value notification is received from the adjacent peer in response to the index value request transmitted by the index value request transmitting unit 71, the file duplication control unit 41 determines the communication device that is the transmission source of the index value notification and the index value. The index value calculation unit 42 is notified. Further, when an index value request is received from an adjacent peer, in response to this, its own index value acquired from the index value calculation unit 42 is returned to the communication device that is the transmission source of the index value request.

  Next, the duplication necessity determination executed by the file duplication control unit 41 in this embodiment will be described with reference to FIG. The number of adjacent peers with which the communication apparatus 1 can directly communicate is called an order and is represented by d, and the access load of each adjacent peer is represented by Li (i = 1, 2,..., D). However, d is a natural number. The communication device 1d is an adjacent peer of the communication device 1 and has the same configuration as that of the communication device 1 of FIG. 3, and the reference numerals of the respective parts are the reference numerals of the corresponding parts of the communication device 1 appended with “d”. And

  Following or in parallel with step S103 described above, the file replication control unit 41 transmits an index value request to each of the communication devices of the adjacent peers via the communication network 6 using the index value request transmission unit 71. (Step S201).

  When the index value request receiving unit 73d receives the index value request in the communication device 1d of the adjacent peer, the file replication control unit 41d transmits the index value notification to the communication device 1 via the communication network 6 by the index value notification transmitting unit 74. To do.

  In the communication apparatus 1, when the index value notification receiving unit 72 receives this index value notification (step S202), the file duplication control unit 41 sets the secondary change amount of the access rate to D · L = (1 / d) Σ. (Li-L) is calculated (sum is i = 1 to d) (step S203). D is an operator for obtaining the secondary change amount.

  Next, the file duplication control unit 41 calculates the probability of duplicating the file as p = (1/2) + (1/2) tanh (μ + λarctanh (D · L)) based on the secondary change amount. (Step S204). Here, μ and λ are parameters. λ is a parameter related to load distribution performance, and μ is a parameter related to search performance.

  Next, the file replication control unit 41 generates a random number R (0 ≦ R <1) (step S205). If the random number R is smaller than p (R <q), the file is stored in the file storage device 5 (step S205). If the random number R is larger than p (R ≧ q), it is determined to discard the file (step S208).

  Referring now to FIG. 2, after determining whether or not duplication is necessary, the file duplication control unit 41 notifies the index value calculation unit 42 whether or not the file has been stored in the file storage device 5. Here, it is assumed that whether the file is stored in the file storage device 5 is represented by I ′, where I ′ = 1 is stored, and where I ′ = 0 is discarded.

  In response to this notification, the index value calculation unit 42 uses I ′ to update the history information held in the reference information storage device 43 (step S106). The reference information storage device 43 sequentially stores N I (t) corresponding to the average time width. Among these, the oldest I (t) is discarded and a new I (t) is added. .

  According to the present embodiment, copies of the same file are arranged in a plurality of peers, so that each peer can perform a search quickly and reliably. Further, since the probability of duplicating the file is changed from the secondary change amount D · L of the access load so as to smooth the local difference in access load between adjacent peers, the frequency of writing to the file storage device 5 Can be distributed among communication devices. Furthermore, system performance such as search performance and load distribution performance can be adjusted by adjusting the parameters μ and λ.

  Next, Example 2 will be described. In the first embodiment, I (t) indicating whether or not a file received from another communication device in a bucket relay format is written in its own file storage device within a unit time is stored for the last N unit times. The access load L was obtained as the average value. On the other hand, in this embodiment, the current access load is obtained based on I (t) recorded for the latest one unit time and the access load obtained last time. Since the reference information storage method in the reference information storage device 43 and the index value calculation method in the index value calculation unit 42 are the same as those in the first embodiment, description thereof will be omitted.

  The reference information storage device 43 writes whether or not a file received in a bucket relay manner from another communication device within the previous unit time has been written to its own file storage device 5 and the access previously calculated by the index value calculation unit 42 Memorize the load. Whether or not writing has recently been performed during one unit time is represented by Ipast, indicating that writing has been performed with Ipast = 1, and indicating that writing has not been performed with Ipast = 0. In addition, the access load previously calculated by the index value calculation unit 42 is set to Lpast. At this time, the reference information storage device 43 holds Ipast and Lpast. The Ipast and Lpast stored in the reference information storage device 43 are updated every unit time. The Ipast and Lpast are discarded every time the unit time elapses, and the presence / absence of replication and the access load in the current unit time are held as new Ipast and Lpast.

  In step S103 of FIG. 2, the index value calculation unit 42 calculates the current access load L to L = (1 / N) (Ipast + (N−) based on Ipast and Lpast held in the reference information storage device 43. 1) Calculate as Lpast). Further, in step S106 of FIG. 2, the index value calculation unit 42 updates Ipast and Lpast currently held in the reference information storage device 43 based on the presence / absence of duplication I and the access load L in the current unit time.

  Using the access load L thus obtained, the file duplication control unit 41 performs the duplication necessity determination described with reference to FIG.

  According to the present embodiment, the same effect as in the first embodiment can be obtained. Further, in the first embodiment, it is necessary to store whether or not duplication has been performed as reference information for the past N unit times. In the present embodiment, whether or not duplication has been performed within the immediately preceding unit time is previously calculated. Since only the access load needs to be stored, the capacity required to hold the reference information can be reduced.

  The present invention has been described based on the embodiments and examples. However, the present invention is not limited to this, and can be appropriately changed within the scope of the technical idea of the present invention. .

  For example, in the first and second embodiments, history information indicating whether or not a file received from another communication device in a bucket relay format is written to its own file storage device within a unit time is used as reference information. The present invention is not limited to this. For example, in order to transmit in response to a request from the other communication device, the communication device generates a copy of the shared file held in its file storage device. It is good also as using the information recorded for every unit time within a predetermined period as reference information.

  In the first and second embodiments, the history information / reference information is updated when a file is received from another communication device in a bucket relay manner. However, the present invention is not limited to this, and for example, the file F Is received from the other communication device B, and the file F is transmitted to the communication device B in response to the search request / transfer request. The communication device A may update its own history information / reference information.

1 is a block diagram of a peer-to-peer communication system 100 according to an embodiment of the present invention. 3 is a flowchart for explaining the operation of the peer-to-peer communication system 100. 1 is a block diagram of a peer-to-peer communication system 200 that is Embodiment 1 of the present invention. FIG. 3 is a flowchart for explaining the operation of the peer-to-peer communication system 200.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Communication apparatus 2 Search request part 3 File transfer part 4 File duplication part 5 File storage device 6 Communication network 21 Search request control part 22 Search request reception part 23 Search request transmission part 31 File transfer control part 32 Transfer file reception part 33 Transfer file Transmission unit 41 File replication control unit 42 Index value calculation unit 43 Reference value storage device 71 Index value request transmission unit 72 Index value notification reception unit 73 Index value request reception unit 74 Index value notification transmission unit

Claims (18)

Whether a peer of a peer-to-peer communication system that stores a copy of the same file in multiple peer storage devices replicates the file to keep the files to be transmitted to the other peer in the peer storage device In the method of determining
The reference information storage device of the peer includes reference information including history information that is information indicating whether or not a file received in a bucket relay manner from the other peer in a predetermined period is written to the storage device of the peer. Remembering, and
In the processing device of the peer, calculate an index value related to temporal change of one or more of the reference information, receive the index value calculated by the processing device of the adjacent peer adjacent to the peer from the adjacent peer, Calculating a binary or probabilistic representation of the necessity of copying a file based on the index value of the peer and the index value of the adjacent peer;
The peer processing device determines whether the file needs to be copied based on a binary or stochastic representation of whether the file needs to be copied, or
And a step of updating the reference information stored in the reference information storage device by the processing device of the peer in accordance with the result of the determination. In the file duplication necessity judgment method according to claim 1,
A probability generation step for determining a probability of holding the file based on at least one of the reference information and the index value;
Generating a random number;
Determining whether or not to hold the file based on the probability and random number. 3. The file duplication necessity determination method according to claim 1, wherein the file received by the peer in a bucket relay manner from the other peer in a unit time is written to the storage device of the peer. A file duplication necessity determination method characterized in that information relating to no is included in reference information. In File Replication necessity determination method according to any one of claims 1 to 3, include the peer has been made to the shared file containing the information relating to presence of the transfer request in the unit time reference information A file duplication necessity judgment method characterized by: In the file duplication necessity judgment method according to any one of claims 1 to 4 ,
Further comprising the step of holding the index value calculated by the peer in a storage device;
The determination step includes performing determination based on the index value stored in the storage device and the index value calculated in the calculation step. In a communication device functioning as a peer of a peer-to-peer communication system that stores a copy of the same file in a plurality of peer storage devices,
Means for storing reference information including history information, which is information indicating whether or not a file received in a bucket relay manner from the other peer in a predetermined period is written to the storage device of the peer;
In the processing device of the peer, calculate an index value related to temporal change of one or more of the reference information, receive the index value calculated by the processing device of the adjacent peer adjacent to the peer from the adjacent peer, Means for calculating a binary or probabilistic value representing the necessity of copying a file based on the index value of the peer and the index value of the adjacent peer;
Means for determining the necessity of copying of the file based on a binary or probabilistic value representing the necessity of copying of the file;
Means for updating reference information stored in the storage device in accordance with a result of the determination. The communication device according to claim 6 , wherein the determination unit includes:
Determining a probability of holding the file based on at least one of the reference information and the index value;
Generate random numbers,
A communication apparatus that determines whether to hold the file based on the probability and a random number. 8. The communication apparatus according to claim 6 , wherein information relating to whether or not the file received by the peer in a bucket relay manner from the other peer within a unit time is written to the storage device of the peer. Is included in the reference information. The communication device according to any one of claims 6 to 8, characterized in that it contains the peer has been made to the shared file containing the information relating to the presence or absence of request for transfer in a unit time reference information Communication device. The communication device according to any one of claims 6 to 9 ,
A means for holding an index value calculated by the peer;
The communication device according to claim 1, wherein the determination unit makes a determination based on the index value held in the unit holding the index value and the index value calculated by the calculation unit. In a computer program for causing a computer to function as a peer in a peer-to-peer communication system that stores a copy of the same file in a plurality of peer storage devices,
Means for storing reference information including history information, which is information indicating whether or not a file received in a bucket relay manner from the other peer in a predetermined period is written to the storage device of the peer;
In the processing device of the peer, calculate an index value related to temporal change of one or more of the reference information, receive the index value calculated by the processing device of the adjacent peer adjacent to the peer from the adjacent peer, Means for calculating a binary or probabilistic value representing the necessity of copying a file based on the index value of the peer and the index value of the adjacent peer;
Means for determining the necessity of copying of the file based on a binary or probabilistic value representing the necessity of copying of the file;
A computer program for functioning as means for updating reference information stored in the storage device in accordance with the result of the determination. 12. The computer program according to claim 11 , wherein the determination means is
Means for determining a probability of holding the file based on at least one of the reference information and the index value;
Means for generating a random number;
A computer program that causes a computer to function as means for determining whether to hold the file based on the probability and a random number. Information in a computer program according to any one of claims 11 through 12, which in a unit time, the file in which the peer receives a bucket brigade from the other peers, according to whether it has written to the storage device of the peer Is included in the reference information. The computer program according to any one of claims 11 to 13, characterized in that it comprises the peer has been made to a shared file that holds the information according to the presence or absence of request for transfer in a unit time reference information Computer program. The computer program according to any one of claims 11 to 14 ,
A computer program for causing a computer to further function as means for holding an index value calculated by the peer,
The determination means causes the computer to function as an index value held in the means for holding the index value and a means for making a determination based on the index value calculated by the calculation means. . Recording medium for recording a computer program according to any one of claims 11 to 15. A computer comprising the recording medium according to claim 16 and operating according to the computer program. Peer-to-peer communication system a peer one described computer to the communication apparatus and claim 17 according to claim 6 to 10.

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