分布式所有課件含

1、NamingChapter 4A general naming graph with a single root node.Name Space Distribution (1)An example partitioning of the DNS name space, including Internet-accessible files, into three layers.Name Space Distribution (2)A comparison between name servers for implementing nodes from a large-scale name s

2、pace partitioned into a global layer, as an administrational layer, and a managerial layer.ItemGlobalAdministrationalManagerialGeographical scale of networkWorldwideOrganizationDepartmentTotal number of nodesFewManyVast numbersResponsiveness to lookupsSecondsMillisecondsImmediateUpdate propagationLa

3、zyImmediateImmediateNumber of replicasManyNone or fewNoneIs client-side caching applied?YesYesSometimesImplementation of Name Resolution (1)The principle of iterative name resolution.Implementation of Name Resolution (2)The principle of recursive name resolution.Implementation of Name Resolution (3)

4、Recursive name resolution of . Name servers cache intermediate results for subsequent lookups.Server for nodeShould resolveLooks upPasses to childReceives and cachesReturns to requestercs#-#vu#nl#root#Implementation of Name Resolution (4)The comparison between recursive and iterative name resolution

5、 with respect to communication costs.The DNS Name SpaceThe most important types of resource records forming the contents of nodes in the DNS name space.Type of recordAssociated entityDescriptionSOAZoneHolds information on the represented zoneAHostContains an IP address of the host this node represen

6、tsMXDomainRefers to a mail server to handle mail addressed to this nodeSRVDomainRefers to a server handling a specific serviceNSZoneRefers to a name server that implements the represented zoneCNAMENodeSymbolic link with the primary name of the represented nodePTRHostContains the canonical name of a

7、hostHINFOHostHolds information on the host this node representsTXTAny kindContains any entity-specific information considered usefulDNS Implementation (1)An excerpt from the DNS database for the zone cs.vu.nl.DNS Implementation (2)Part of the description for the vu.nl domain which contains the cs.vu

8、.nl domain.NameRecord typeRecord valuecs.vu.nlNISsolo.cs.vu.nlsolo.cs.vu.nlAThe X.500 Name Space (1)A simple example of a X.500 directory entry using X.500 naming conventions.AttributeAbbr.ValueCountryCNLLocalityLAmsterdamOrganizationLVrije UniversiteitOrganizationalUnitOUMath. & Comp. Sc.CommonName

9、CNMain serverMail_Servers-, 192.31.231,6FTP_Server-1WWW_Server-1The X.500 Name Space (2)Part of the directory information tree.The X.500 Name Space (3)Two directory entries having Host_Name as RDN.AttributeValueAttributeValueCountryNLCountryNLLocalityAmsterdamLocalityAmsterdamOrganizationVrije Unive

10、rsiteitOrganizationVrije UniversiteitOrganizationalUnitMath. & Comp. Sc.OrganizationalUnitMath. & Comp. Sc.CommonNameMain serverCommonNameMain serverHost_NamestarHost_NamezephyrHost_Address2Host_Address6Naming versus Locating EntitiesDirect, single level mapping between names and addresses.T-level m

11、apping using identities.Forwarding Pointers (1)The principle of forwarding pointers using (proxy, skeleton) pairs.Forwarding Pointers (2)Redirecting a forwarding pointer, by storing a shortcut in a proxy.Home-Based ApproachesThe principle of Mobile IP.Hierarchical Approaches (1)Hierarchical organiza

12、tion of a location service into domains, each having an associated directory node.Hierarchical Approaches (2)An example of storing information of an entity having two addresses in different leaf domains.Hierarchical Approaches (3)Looking up a location in a hierarchically organized location service.H

13、ierarchical Approaches (4)An insert request is forwarded to the first node that knows about entity E.A chain of forwarding pointers to the leaf node is created.Pointer Caches (1)Caching a reference to a directory node of the lowest-level domain in which an entity will reside most of the time.Pointer

14、 Caches (2)A cache entry that needs to be invalidated because it returns a nonlocal address, while such an address is available.Scalability IssuesThe scalability issues related to uniformly placing subnodes of a partitioned root node across the network covered by a location service.The Problem of Un

15、referenced ObjectsAn example of a graph representing objects containing references to each other.Reference Counting (1)The problem of maintaining a proper reference count in the presence of unreliable communication.Reference Counting (2)Copying a reference to another process and incrementing the cou

16、nter too lateA solution.Advanced Referencing Counting (1)The initial assignment of weights in weighted reference countingWeight assignment when creating a new reference.Advanced Referencing Counting (2)Weight assignment when copying a reference.Advanced Referencing Counting (3)Creating an indirection when the partial weight of a reference has reached