测绘学报

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基于开销代价的网络地理信息服务负载均衡算法研究

王浩,潘少明,喻占武,李锐   

  • 收稿日期:1900-01-01 修回日期:1900-01-01 出版日期:2011-12-28 发布日期:2019-01-01

Cost based Load Balancing for Network Quality of GIS

WANG Hao,PAN Shao-ming,YU Zhan-wu,LI Rui   

  • Received:1900-01-01 Revised:1900-01-01 Online:2011-12-28 Published:2019-01-01

摘要: 三维地形漫游成为当今网络GIS的热门应用,大规模、高强度的访问请求给服务器端的地形数据提取提出了挑战。为快速响应地形数据请求,集群服务器技术被广泛应用。根据不同的GIS数据请求以及服务器状态信息选择合适的服务器处理请求是集群负载均衡算法面临的重要问题。传统的算法要么未考虑服务器状态信息造成转发决策具有盲目性,要么过度使用服务器实时状态信息造成大量收集与维护开销,不适合高强度的地形漫游。基于单位时间开销代价矢量,提出了同时考虑地形数据请求在服务器队列中的等待时间与服务器对请求的处理时间的最小总代价分布式算法。算法计算转发请求给每台服务器的概率空间,并根据地形数据请求到达时临时生成的随机数在概率空间中的落点确定转发请求的目标服务器。通过配置单位时间开销代价矢量,可以灵活地维护与升级集群服务器,具有良好的可扩展性。仿真结果表明最小总代价算法能在大规模、高强度的地形漫游中均衡地分发请求,使集群服务器充分发挥其优势从而获得最小的漫游响应时间。仿真结果还表明在低强度地形漫游时,各种负载均衡算法表现大致相同;在高强度地形漫游时,设计负载均衡算法最好考虑服务器端队列的排队情况。

Abstract: Three-dimensional terrain navigation is a hot application in network quality of geographic information system (GIS), large-scale and high intensity requests of which from clients have posed challenge on terrain data process in GIS servers. Servers are clustered to quicken terrain data response. The success factor of clustered servers is load balancing, which chooses an appropriate server to process requests by considering the type of requests and the status information of servers. Traditional load balancing algorithms either ignore server status resulting in blindness of dispatch decision, or overuse server status causing large overhead in its gather and maintenance. A distributed least cost algorithm is proposed by taking into account the waiting time of terrain data request in server queue and the process time of it in server, based on unit time cost vector. Dispatch probability space for each server is calculated and target server is determined through the landing point of a temporarily generated random number in the probability space. The scalability of the algorithm is satisfactory and the maintenance and update of clustered servers is flexible by configure the unit time cost vector. Extensive simulation indicates that for large-scale and high intensity terrain tile requests the least cost algorithm can balance servers efficiently and response the requests with minimal time. Simulation result also shows that under low intensity requests, the considered load balancing algorithms behave approximately the same, while under high intensity request, it is better to design load balancing by considering queue situation of clustered servers.