Coarse-grain replica management strategies for dynamic replication of Web contents

Abstract

This paper discusses replica management strategies for cost-effective, scalable Web content distribution. In terms of the granularity of replica contents, current dynamic replication approaches can be classified into entire replication (entire content is replicated) and object replication (individual objects are replicated) schemes. However, while the former cannot effectively reduce client download time and server load due to the coarsest replication granularity, the latter requires a large overhead to manage replica locations due to per-object request redirection. We propose schemes to deliver almost as effective performance to reduce download time and server load as in the object replication scheme while they require almost as small overhead to manage replica locations as the entire replication scheme. The schemes aggregate objects in the origin server into multiple content groups and then replicate them on per-group granularity. Per-group request redirection can significantly reduce an overhead to manage replica locations. The content groups are either statically created in advance or dynamically created upon replication. The approach of dynamic grouping uses a URL rewriting technique to enable per-group request redirection. We evaluate the performance to reduce download time and server load in the proposed schemes changing the number of created content groups. The scheme of dynamic group creation achieves almost the same performance characteristic to reduce download time as the object replication scheme with a significantly smaller overhead to manage replica locations. Even the scheme of static group creation provides much better performance than entire replication under a skewed request distribution. The proposed scheme, which addresses URL inconsistency problems derived from the URL rewriting, preserves high download time reduction performance with insignificant overhead of replica management.