4.4 Probe and Match
4.4 探測(cè)和匹配
A pattern used for discovery of services is the Probe and Match pattern.In this variation,shown in Figure 4-4,a single client may multicast or broadcast a message to several endpoints on a single fabric,prompting them to respond based on certain criteria.For example,this pattern may be used to determine whether large numbers of servers on a server farm are capable of handling more traffic by checking if they are scaled at less than 50% capacity.This variation of the SOA message exchange pattern may also be used to locate specific services.There are caveats with using such a pattern,as it may become bandwidth-intensive if used often.Utilizing a registry or another centralized metadata facility may be a better option because the registry interaction does not require sending the probe() messages to all endpoints to find one.By convention,they allow the query to locate the endpoint using a filter query or other search algorithm.
探測(cè)和匹配模式就是用來(lái)搜索服務(wù)的.在此模式下(如圖4-4),一個(gè)單一的客戶端可以給單一結(jié)構(gòu)上的幾個(gè)服務(wù)端組播或廣播一條消息,促使這些服務(wù)端基于某些條件進(jìn)行應(yīng)答.例如,此模式可以用于決定服務(wù)器群中大量的服務(wù)器是否有能力處理更多是數(shù)據(jù)流量,即檢查這些服務(wù)器的存儲(chǔ)能力是否低于50%.作為SOA信息交換模式中的一種,它還可以用來(lái)鎖定特殊的服務(wù).但是,使用此模式要注意的事項(xiàng)是,經(jīng)常使用該模式的話,對(duì)帶寬要求很高.而用注冊(cè)表型或者其他集中元數(shù)據(jù)型可能是一個(gè)更好的選擇,因?yàn)樽?cè)表式交互模式不需要發(fā)送探測(cè)信息給所有的服務(wù)端只為找一項(xiàng)服務(wù).通過(guò)對(duì)話,它們(即注冊(cè)表模式和采用其他集中元數(shù)據(jù)技術(shù)的模式)利用一種篩選查詢方式或者其他搜索方式來(lái)查詢并瑣定服務(wù)端.
In the Probe and Match scenario in Figure 4-4,the service client probes three services,yet only the middle one returns an associated match() message.A hybrid approach could use the best of both the registry and the probe and match models for locating service endpoints.In the future,registry software could implement a probe interface to allow service location without requiring wire transactions going to all endpoints and the searching mechanism could probe multiple registries at the same time.
在圖4-4所示的探測(cè)和匹配方案中,服務(wù)客戶端探測(cè)三個(gè)服務(wù)端,只有中間那個(gè)給出了相應(yīng)的匹配信息.最好的方法是把注冊(cè)模式與探測(cè)和匹配模式組合起來(lái),用于鎖定服務(wù)端.在將來(lái),注冊(cè)模式的軟件可以運(yùn)行一個(gè)探測(cè)界面,允許服務(wù)定位不需要查詢,而是連接到所有服務(wù)端;同樣的,搜索引擎可以探測(cè)多重注冊(cè)表.
4.5 Patterns for RIAs
4.5 RIAs模式
Creating Rich Internet Applications (RIAs) requires a level of data management that goes beyond the traditional Request-Response model.Providing a richer,more expressive experience often requires more data-intensive interaction and introduces new challenges in managing data between the client and server tiers.
"創(chuàng)建密集互聯(lián)網(wǎng)應(yīng)用系統(tǒng)"(RIAs) 需要的數(shù)據(jù)管理水平,超越了傳統(tǒng)的"要求-反應(yīng)模式".對(duì)于一個(gè)密集型客戶,更具表現(xiàn)力的體驗(yàn)通常需要更多的數(shù)據(jù)密集式交互,這給客戶端和服務(wù)層之間的數(shù)據(jù)管理提出了新的挑戰(zhàn).
Data synchronization is a key concept and requires states to be shared among multiple machines.These are usually the clients who have subscribed to the state of an object somewhere within the tier of a distributed system as depicted in Figure 4.5.
在多機(jī)并行中,數(shù)據(jù)同步是一個(gè)重要的概念和必要的狀態(tài).通常情況下,客戶們制訂一個(gè)目標(biāo)狀態(tài),這個(gè)目標(biāo)位于一個(gè)分散系統(tǒng)的某個(gè)服務(wù)層之中,如圖4.5所示.