CN103888517B - Caching method for publishing and subscription system to achieve historical event subscription - Google Patents
Caching method for publishing and subscription system to achieve historical event subscription Download PDFInfo
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- CN103888517B CN103888517B CN201410075650.2A CN201410075650A CN103888517B CN 103888517 B CN103888517 B CN 103888517B CN 201410075650 A CN201410075650 A CN 201410075650A CN 103888517 B CN103888517 B CN 103888517B
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Abstract
The invention discloses a caching method for a publishing and subscription system to achieve historical event subscription. The method includes the following steps of extending a route table, wherein cache routing information is added to the route table; processing events and calculating a caching point reference value through a hash function; publishing the events, wherein whether a current agent node serves as a cache point and carries out caching is judged through the caching point reference value, and cache routing information is updated synchronously; caching subscription; obtaining caches. The caching method has the advantages that subscription of historical events of subscribers is achieved, storage space of agents or neighbor agents on an event dispatching path are fully used, the utilization rate of storage resources is improved, caching capacity of the publishing and subscription system is enhanced, cache redundancy is simplified, and balance between visit and storage efficiency and the storage occupancy rate is achieved.
Description
Technical field
The present invention relates to distribution subscription system technology is and in particular to a kind of realize the caching method that historical events are subscribed to.
Background technology
Distribution subscription system comprises a distributed communication network, i.e. event agent's network, and a series of is in communication with each other
End points, i.e. subscriber and publisher.Pass through event agent's network interconnection, using a kind of asynchronous between subscriber and publisher
Publish-subscribe mode is completing data exchange.Subscriber passes through to state that a filtercondition expression formula submits subscription to, works as publisher
Issue an event meeting its subscription condition, this event is routed to subscriber via agency network.In time, content
Subscription with to issue be asynchronous, and spatially, subscriber and publisher also need not be concerned about that other side is located at where, therefore issues
It is full decoupled in space, time and controlling stream that ordering system achieves communicating pair.
In traditional distribution subscription system, event notifies to be able to ensure that and eventually arrives at each subscriber interested, but
Premise is each subscriber all in presence and respective subscription is known to whole system.This precondition is for dynamic
It is then one to limit greatly for network environment, because client often continually adds or leaves network, the new subscriber adding
An event issued before it adds network may be asked.In traditional distribution subscription system, this request is
Cannot respond, thus how using event buffer mechanism so that new user can know that historical events just become issue and order
System of readding needs the big problem solving.
Content of the invention
In order to overcome subscriber present in prior art cannot subscribe to the defect of historical events, the present invention provides a kind of real
The caching method that existing historical events are subscribed to.The specific technical scheme of the present invention is as follows:
A kind of caching method realizing historical events subscription for distribution subscription system, comprises the steps:
Routing table expands step: sets up buffering route information in the routing table of each agent node, described cache routing letter
Cease for providing the routing iinformation that can navigate to buffer；
Event processing steps: when a certain agent node sends an event, calculated by hash function, obtain one and delay
Deposit a reference value；Add a message header for described event, have recorded buffer information in described message header and subscribe to path letter
Breath；Described buffer information includes described buffer reference value；
Event issuing steps: according to the subscription routing information of record in described message header, described event is ordered to corresponding
Read node to be issued；For each agent node in issuing path, current agent is judged according to described buffer reference value
Whether node goes forward side by side row cache as buffer, and meanwhile, current agent node synchronized update corresponds to the cache way of described event
By information；
Caching subscription step: a certain agent node sends a cache request, comprises subscription condition in described cache request；Will
Described subscription condition is mated with the filtercondition prestoring in the routing table of current agent node, determines caching event；Described
Caching event refers to, event corresponding with the subscription condition filtercondition that the match is successful；
Caching obtaining step: if comprising described caching event corresponding cache routing letter in the routing table of current agent node
Breath, then directly find the corresponding buffer of described caching event according to this buffering route information, cache request be forwarded to caching
Point, obtains caching；If not comprising the corresponding buffering route information of described caching event, root in the routing table of current agent node
According to the corresponding subscription routing iinformation of described caching event, cache request is sent to next agent node, revolution executes caching
Obtaining step.
As prioritization scheme, shown in described hash function such as formula (1):
The domain of definition of this hash function is the span (a, b) of event e, and codomain is [0, max_hop]；Wherein max_
Hop is the ultimate range to its root node for the agent node on case distribution path.
Calculated buffer reference value is an integer value.
As prioritization scheme, judge current agent node whether as buffer and carry out according to described buffer reference value
Caching particularly as follows:
Described buffer reference value t is first subtracted 1 after receiving event by current agent node, is then entered according to buffer reference value
Row judges, if t=0, by current agent node as buffer.
As prioritization scheme, described routing table expand step particularly as follows:
Increase cache_nexthops field so that the structure of described routing table is in the routing table of each agent node:
<filter|sub_nexthops|cache_nexthops>
Wherein, filter refers to filtercondition, and sub_nexthops have recorded with the filter event that the match is successful to ordering
Read the next-hop agency of node direction forwarding, cache_nexthops have recorded with the filter cache request that the match is successful to slow
Deposit the next-hop agency of a direction forwarding.
As prioritization scheme, in described event issuing steps, for current agent node in issuing process for the event, its
The update method of buffering route information particularly as follows:
If current agent node, at the rear of buffer, the next-hop in buffering route information is set to the generation of forerunner
Reason node；
If current agent node is just buffer, the next-hop in buffering route information is set to current agent section
Point itself；
If current agent node, in the front of buffer, the next-hop in buffering route information is set to follow-up generation
Reason node.
As prioritization scheme, in described caching obtaining step, cache request is forwarded to the method that buffer obtains caching
Particularly as follows:
Record, during cache request is forwarded to buffer, the agent node passing through on the way successively, be designated as cache request
Path；Cache request reach buffer after, buffer by ask caching along cache request path backward be sent to send slow
Deposit the agent node of request.
As prioritization scheme, in described event issuing steps, if current agent node as buffer go forward side by side row cache when,
Judged: if the memory space of current agent node exhausts, inquire immediate neighbor outside this event issuing path whether
Still there is free memory；If this neighbour has free memory, event forwarding is entered row cache to this neighbour.
As prioritization scheme, described buffer information also includes buffer position, cached copies number and cache-time
Stamp, the initial value of described buffer position, cached copies number and cache-time stamp is sky；For each in issuing path
Agent node, if current agent node as buffer go forward side by side row cache when, in the message header of update event record buffer
Position, cached copies number and cache-time stamp, the buffer position, the caching that update the storage of current agent node memory secondary simultaneously
This number and cache-time stamp.
As prioritization scheme, in event in issuing process, the cache-time stamp of more each agent node, obtains the most on the way
The position of old caching, when event arrives at subscription node, if the memory space on whole piece issuing path exhausts, transfers back to oldest
Oldest caching is deleted in the position of caching.
As prioritization scheme, in described event issuing steps, for each agent node, using redundancy reduction method to thing
Part enters row cache, described redundancy reduction method particularly as follows:
If agent node is bi, it comprises some child nodes bijIf, gijFor each child node bijCorresponding subtree；According to
Object functionDetermined which subtree that the copy of caching is assigned to buffer, such as shown in formula (2):
Wherein, dijRepresent agent node btApart from subtree gijThe ultimate range of terminal temperature difference, rijRepresent agent node btConnect
Receive from subtree gijUser's request sum, sijRepresent subtree gijIn the total storage idleness of all nodes, t be buffer
Reference value；Object functionMolecule represent a Replica placement of event in subtree gijWhen upper, user obtains this copy
Overhead；Wherein, the Section 1 of molecule is subtree gijExpense during this copy of the user's request of end, the Section 2 then table of molecule
Show remaining subtreeOn this copy of user's request when overhead；
Agent node btFor each child node bijRespectively calculate a targetSelect its value minimum m=min { k, ni}
Stalk tree gt1, gt2..., gtmAssign copy, and correspondingly will be sent to child node bt1, bt2..., btmEvent copy number
K modifies according to formula (3):
Other child nodes b will be sent tottCopy number k of event be set to ki=0 (m ＜ l≤nt), corresponding t value returns 0.
Compared with prior art, the method have the advantages that
(1) caching method that the present invention provides achieves the subscription to historical events for the subscriber；
(2) present invention takes full advantage of the memory space of all agencies and its neighbours agency on case distribution path, improves
Utilization ratio of storage resources, enhances the caching capabilities of distribution subscription system；
(3) present invention simplifies to caching redundancy, balances between memory access efficiency and storage occupancy.
Brief description
The general flow chart of the caching method that Fig. 1 provides for the present invention；
Fig. 2 is the network diagram of distribution subscription system in embodiment 1.
Specific embodiment
Describe the present invention below in conjunction with the accompanying drawings by way of example in detail.
Embodiment 1:
As shown in figure 1, a kind of caching method realizing historical events subscription for distribution subscription system, walk including following
Rapid:
Step s1, routing table expands step: sets up buffering route information in the routing table of each agent node, described caching
Routing iinformation is used for providing the routing iinformation that can navigate to buffer.
In traditional distribution subscription system, comprise in the routing table of each agent node to subscribe to routing iinformation, for positioning
To the corresponding subscriber of event；In order that distribution subscription system supports caching, on this basis, set up buffering route information, right
Routing table is extended.
Existing router-table structure is ＜ filter | sub_nexthops >, wherein filter is filtercondition, sub_
Nexthops then have recorded with the filter event that the match is successful to the next-hop agent node subscribing to node direction forwarding；Should
Sub_nexthops field corresponds to and subscribes to routing iinformation.
Increase cache_nexthops field so that the structure of described routing table is in existing router-table structure:
＜ filter | sub_nexthops | cache_nexthops ＞
Wherein, cache_nexthops have recorded with the filter cache request that the match is successful to buffer direction forwarding
Next-hop is acted on behalf of, and this cache_nexthops field corresponds to buffering route information.This cache_nexthops field is in thing
Construct along distribution path hop-by-hop in part issuing process, effect is that the cache request for user provides routing iinformation so as to can look for
To buffer, as sub_nexthops helps event to find subscriber.
Step s2, event processing steps: when a certain agent node sends an event, calculated by hash function,
Obtain a buffer reference value；Add a message header for described event, have recorded buffer information in described message header and order
Read routing information；Described buffer information includes described buffer reference value.
This step be publisher to before subscriber's transmission event, in order to realize caching and the process that carries out.Hypothesis event e
Span be e, value ∈ (a, b), publisher is determined which on path of event buffer by following hash function
A little nodes, such as shown in formula (1):
Wherein, the domain of definition of this hash function is event e span (a, b), and codomain is then [0, max_hop], its
Middle max_hop is that the ultimate range of the agent node on case distribution path to its root node (can be disappeared by prior transmission exploration
Breath obtains), in terms of jumping figure.When event e does not have distribution path, it is mapped to the 0th jump, i.e. root node.
It is calculated buffer reference value, this buffer reference value is an integer value.The result of Hash mapping obtains
The agent identifier of buffer reference value not buffer, but the jumping figure variable t of a similar subtraction count device, record be
The buffer of this event and the distance of current agent node.After carrying out Hash operation, which agency's section can not be determined at once
Point is buffer, needs, in event issuing process, to be determined according to buffer reference value by each agent node on issuing path
Whether itself is as buffer.By the buffer calculating reference value record in the message header of event, issue with event.
Subscription routing information have recorded event and is sent to subscriber's routing information to be passed through from publisher.
Step s3, event issuing steps: according to the subscription routing information of record in described message header, by described event to right
The subscription node answered is issued；For each agent node in issuing path, judge to work as according to described buffer reference value
Whether front agent node goes forward side by side row cache as buffer, and meanwhile, current agent node synchronized update corresponds to described event
Buffering route information.
In this step, judge that whether current agent node goes forward side by side row cache tool as buffer according to buffer reference value
Body is:
Buffer reference value t is first subtracted 1 after receiving event by current agent node, is then judged according to its value, if t=
0, then current agent node is i.e. as buffer.
When entering row cache it is possible to current agent node occurs the full situation of memory space, in order to make full use of
Memory space in network, before entering row cache, makes the following judgment: if the memory space of current agent node exhausts,
Inquire whether the immediate neighbor outside this event issuing path still has free memory；If this neighbour has free memory,
Then event forwarding is entered row cache to this neighbour.The utilization rate of the memory space of whole system can be improved using the method.
, after completing buffer and judging, needing should in the routing table of synchronized update current agent node for current agent node
The corresponding buffering route information of event.The update method of buffering route information is specifically, include three kinds of situations: and relative configurations are slow
Deposit route:
Situation one: if t ＜ 0, that is, through buffer, current agent node is located at the downstream of buffer for the forwarding of event,
Then the next-hop in buffering route information is set to the agent node of forerunner；
Situation two: if t=0, that is, current agent node is just buffer, then set the next-hop in buffering route information
It is set to current agent node itself；
Situation three: if t ＞ 0, i.e. the forwarding of event does not also reach buffer, current agent node in the front of buffer,
Then the next-hop in buffering route information is set to follow-up agent node.
All carry out judgement and the buffering route information of above-mentioned buffer in each of event issuing process agent node
The operation updating.When event is sent to subscriber, all of buffer all has determined that row cache of going forward side by side, the institute in issuing path
Agent node is had all to update buffering route information.
Step s4, caches subscription step: a certain agent node sends a cache request, comprises to subscribe in described cache request
Condition；Described subscription condition is mated with the filtercondition prestoring in the routing table of current agent node, is determined caching thing
Part；Described caching event refers to, event corresponding with the subscription condition filtercondition that the match is successful.
In this step, when subscriber access distribution subscription system after, to subscribe to historical events, that is, be intended to from
Required content is subscribed in the event of caching.The subscription request sending during similar to the event of subscription, subscribes to during caching by sending
One cache request is realized.If cache request is requset (δ f), δ f therein is subscription condition.
Step s5, caches obtaining step: if it is corresponding slow to comprise described caching event in the routing table of current agent node
Deposit routing iinformation, then directly the corresponding buffer of described caching event is found according to this buffering route information, cache request is turned
It is dealt into buffer, obtain caching；If not comprising the corresponding cache routing of described caching event in the routing table of current agent node
Information, then according to the corresponding subscription routing iinformation of described caching event, cache request is sent to next agent node, revolution
Execution caching obtaining step.
Specifically, in this step, the two kinds of situations that include that cache are obtained:
(1) comprise the corresponding buffering route information of caching event in routing table, that is, the user subscribing to historical events occurs in
In the distribution path of its interesting event.At this moment cache request can find event buffer point with direct basis cache_nexthops.
Record, during cache request forwarded hop-by-hop to buffer, the agent node passing through on the way successively, be designated as cache request road
Footpath；After cache request reaches buffer, the caching asked is sent to and sends caching along the backward in cache request path by buffer
The agent node of request.
(2) do not comprise the corresponding buffering route information of caching event in routing table, that is, the user subscribing to historical events does not exist
In the distribution path of its interesting event.According to the caching corresponding sub_nexthops of event, cache request is sent to the next one
Agent node.Next agent node repeats aforesaid operations, until finding event buffer point.
The caching method that the present embodiment is provided that cites an actual example below is described in detail, and Fig. 2 gives issue and orders
Read the network diagram of system, wherein, a～e represents 5 agent nodes, p represents the agent node at publisher place, s1Represent
The agent node that user (subscriber) is located.
Assume user s1Filtercondition be f1, publisher p issued one and met filtercondition f1Event e1And select
Act on behalf of d as buffer, e1Take this buffer information to be mated to subscriber's hop-by-hop along distribution path a → b → d → e from publisher
Forward.Act on behalf of a by event and f1The match is successful, reads the buffer information in event message head and finds that its buffer is located at certainly
Own downstream, then adds subscription route next jump node (acting on behalf of b) that the match is successful to cache_nexthops field, shows
The cache lookup request receiving in the future can be transmitted to b.B also can carry out similar operation and look into descendant node d as caching
The next-hop looked for.D finds after receiving event oneself to be chosen as buffer, then by event be stored in local and by oneself add to
Cache routing next-hop.Act on behalf of e and then e is learnt according to the buffer information in event message head1It has been buffered in case distribution road
Upstream in footpath, then using precursor node d as cache routing next-hop.Thus hop-by-hop completes the structure of buffering route information
Make.
Assume a new user s2It is connected to and act on behalf of e request event e1, due to new user s2Occur in event e1Issue
On path, e searches routing table and f1After the match is successful, forward a request to cache next-hop according to cache_nexthops
(acting on behalf of d), thus finding event buffer, is (1st) the kind situation mentioned in step s5.
If s2Acting on behalf of at c, due to new user s2Not in event e1Issuing path on, the c f that the match is successful1Table
There is not buffering route information (nil), at this moment cache request can be turned to subscriber direction by it according to sub_nexthops in
Send out, that is, be transmitted to and act on behalf of b, and b is just at e1Distribution path on, will be able to be asked according to cache routing cache_nexthops
Ask and be transmitted to d, so finally also have found caching, be (2nd) the kind situation mentioned in step s5.Request message forwards
During can record successively on the way id through node, the cache request of user eventually arrives at when acting on behalf of d, wherein contains one
Node link: s2→ c → b, i.e. cache request path.Act on behalf of d to seal the event content that user is asked together with this link
Dress up response message response (e1, s2→ c → b), along link reverse back to user, complete the response of cache request.
Embodiment 2:
The present embodiment is with the difference of embodiment 1, the buffer information in event message head also include buffer position,
Cached copies number and cache-time stamp, each event buffer corresponding cache-time stamp.
Before event is issued, the initial value of described buffer position, cached copies number and cache-time stamp is sky.
In event issuing process, for each agent node in issuing path, if current agent node as buffer and is carried out
During caching, in the message header of update event, the buffer position of record, cached copies number and cache-time stamp, update simultaneously
The buffer position of current agent node memory storage, cached copies number and cache-time stamp.
In actual applications it is possible to situation that memory space in distribution subscription network exhaust occurs, therefore, now
Need to delete some old cachings, discharge memory space and be supplied to new caching.In the present embodiment, specifically using as lower section
Method: in event in issuing process, the cache-time stamp of more each agent node, obtains the position of oldest caching, work as thing on the way
When part arrives at subscription node, if the memory space on whole piece issuing path exhausts, the position transferring back to oldest caching is deleted
Old caching.
Embodiment 3:
In order to simplify to caching redundancy, it is balanced between memory access efficiency and storage occupancy, the present embodiment exists
The method that caching is simplified is added, concrete grammar is as follows on the basis of embodiment 1:
In event issuing steps, for each agent node, row cache is entered to event using redundancy reduction method, described
Redundancy reduction method particularly as follows:
OrderRepresent the set of all agent nodes in case distribution tree,Represent one of case distribution tree
Agent node, wherein, Represent node biAll child node set, wherein,
Each agent node is to comprise some child nodes bij, gijFor each child nodeA corresponding stalk tree, wherein j
=1,2 ..., nt；Represent niThe b that stalk tree collectively formstSubtree collection.
According to object functionDetermined which subtree that the copy of caching is assigned to buffer, such as shown in formula (1):
Wherein, dijRepresent agent node btApart from subtree gijThe ultimate range of terminal temperature difference, rijRepresent agent node biConnect
Receive from subtree gijUser's request sum, sijRepresent subtree gijIn the total storage idleness of all nodes, t be buffer
Reference value；Object functionMolecule represent a Replica placement of event in subtree gijWhen upper, user obtains this copy
Overhead；Wherein, the Section 1 of molecule is subtree gijExpense during this copy of the user's request of end, the Section 2 then table of molecule
Show remaining subtreeOn this copy of user's request when overhead.
Here apart from dtj- t and dti+ t is an approximation, and each agent node cannot learn definitely opening up of subtree
Flutter structure, so it is equivalent to buffer distance to be approximately considered each user.The overhead of cache request is less, or always deposits in subtree
Storage space idleness is bigger, then target function value is less.
Agent node btFor each child node bijRespectively calculate a targetSelect its value minimum m=min { k, nt}
Stalk tree gt1, gt2..., gtmAssign copy, and correspondingly will be sent to child node bt1, bt2..., btmEvent copy number
K modifies according to formula (2):
Other child nodes b will be sent tottCopy number k of event be set to ki=0 (m ＜ l≤nt), corresponding t value returns 0.
Each carries out above-mentioned process as the agent node of buffer, thus being completed in a distributed manner by each agent node
The depositing of cached copies.
A specific embodiment being only the application disclosed above, but the application is not limited to this any this area
What technical staff can think change, all should fall in the protection domain of the application.
Claims (10)
1. a kind of caching method realizing historical events subscription for distribution subscription system is it is characterised in that include following walking
Rapid:
Routing table expands step: sets up buffering route information in the routing table of each agent node, described buffering route information is used
The routing iinformation of buffer can be navigated in offer；
Event processing steps: when a certain agent node sends an event, calculated by hash function, obtain a buffer
Reference value；Add a message header for described event, have recorded buffer information in described message header and subscribe to routing information；Institute
State buffer information and include described buffer reference value；
Event issuing steps: according to the subscription routing information of record in described message header, described event is subscribed to section to corresponding
Point is issued；For each agent node in issuing path, current agent node is judged according to described buffer reference value
Whether go forward side by side row cache as buffer, meanwhile, current agent node synchronized update corresponds to the cache routing letter of described event
Breath；
Caching subscription step: a certain agent node sends a cache request, comprises subscription condition in described cache request；Will be described
Subscription condition is mated with the filtercondition prestoring in the routing table of current agent node, determines caching event；Described caching
Event refers to, event corresponding with the subscription condition filtercondition that the match is successful；
Caching obtaining step: if comprising the corresponding buffering route information of described caching event in the routing table of current agent node,
Then directly the corresponding buffer of described caching event is found according to this buffering route information, cache request is forwarded to buffer,
Obtain caching；If not comprising the corresponding buffering route information of described caching event, basis in the routing table of current agent node
The corresponding subscription routing iinformation of described caching event, cache request is sent to next agent node, and revolution execution caching obtains
Take step.
2. caching method according to claim 1 is it is characterised in that described hash function such as formula (1) is shown:
The domain of definition of described hash function is the span (a, b) of event e, and codomain is [0, max_hop]；Wherein max_hop
It is the ultimate range to its root node for the agent node on case distribution path.
3. caching method according to claim 2 is it is characterised in that judge current agent according to described buffer reference value
Node whether as buffer go forward side by side row cache particularly as follows:
Described buffer reference value t is first subtracted 1 after receiving event by current agent node, is then sentenced according to buffer reference value
Disconnected, if t=0, by current agent node as buffer.
4. caching method according to claim 1 it is characterised in that described routing table expand step particularly as follows:
Increase cache_nexthops field so that the structure of described routing table is in the routing table of each agent node:
<filter|sub_nexthops|cache_nexthops>
Wherein, filter refers to filtercondition, and sub_nexthops have recorded with the filter event that the match is successful to subscription section
The next-hop agency of point direction forwarding, cache_nexthops have recorded with the filter cache request that the match is successful to buffer
The next-hop agency of direction forwarding.
5. caching method according to claim 4 is it is characterised in that in described event issuing steps, sending out for event
Current agent node during cloth, the update method of its buffering route information particularly as follows:
If current agent node, at the rear of buffer, the next-hop in buffering route information is set to agency's section of forerunner
Point；
If current agent node is just buffer, the next-hop in buffering route information is set to current agent node certainly
Body；
If current agent node, in the front of buffer, the next-hop in buffering route information is set to follow-up agency's section
Point.
6. caching method according to claim 5 is it is characterised in that in described caching obtaining step, cache request is turned
Be dealt into buffer obtain caching method particularly as follows:
Record, during cache request is forwarded to buffer, the agent node passing through on the way successively, be designated as cache request road
Footpath；After cache request reaches buffer, the caching asked is sent to and sends caching along the backward in cache request path by buffer
The agent node of request.
7. caching method according to claim 1 is it is characterised in that in described event issuing steps, if current agent section
Point as buffer go forward side by side row cache when, judged: if the memory space of current agent node exhausts, inquire that this event is sent out
Whether the immediate neighbor outside cloth path still has free memory；If this neighbour has free memory, by event forwarding
Enter row cache to this neighbour.
8. caching method according to claim 1 it is characterised in that described buffer information also include buffer position,
Cached copies number and cache-time stamp, the initial value of described buffer position, cached copies number and cache-time stamp is equal
For sky；For each agent node in issuing path, if current agent node as buffer go forward side by side row cache when, update thing
In the message header of part, the buffer position of record, cached copies number and cache-time stamp, update current agent node simultaneously
The buffer position of memory storage, cached copies number and cache-time stamp.
9. caching method according to claim 8 is it is characterised in that in event in issuing process, more each generation on the way
The cache-time stamp of reason node, obtains the position of oldest caching, when event arrives at subscription node, if on whole piece issuing path
Memory space exhausts, then oldest caching is deleted in the position transferring back to oldest caching.
10. caching method according to claim 1 is it is characterised in that in described event issuing steps, act on behalf of for each
Node, enters row cache using redundancy reduction method to event, described redundancy reduction method particularly as follows:
If agent node is bi, it comprises some child nodes bijIf, gijFor each child node bijCorresponding subtree；According to target letter
NumberDetermined which subtree that the copy of caching is assigned to buffer, such as shown in formula (2):
Wherein, dijRepresent agent node biApart from subtree gijThe ultimate range of terminal temperature difference, rijRepresent agent node biReceive
From subtree gijUser's request sum, sijRepresent subtree gijIn the total storage idleness of all nodes, t be buffer reference
Value；Object functionMolecule represent a Replica placement of event in subtree gijWhen upper, user obtains always opening of this copy
Pin；Wherein, the Section 1 of molecule is subtree gijExpense during this copy of the user's request of end, the Section 2 of molecule then represents it
Minor treeOn this copy of user's request when overhead；
Agent node biFor each child node bijRespectively calculate a targetSelect its value minimum m=min { k, niStalk
Tree gi1, gi2..., gimAssign copy, and correspondingly will be sent to child node bl1, bl2..., blmEvent copy number k root
Modify according to formula (3):
Other child nodes b will be sent toiiCopy number k of event be set to kl=0 (m ＜ l≤ni), corresponding t value returns 0.
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