18
3.2
Background
3.2.1
The PRESS Web Server Model
PRESS is an event driven, distributed Web server [23] which exploits user level
communication for efficient communication. This cluster based Web server uses VIA[30]
for intra cluster communication and TCP/IP for intra cluster for communication with
clients. The client requests are directed by a content oblivious webswitch to server
nodes in the cluster by a simple method such as Round Robin DNS. The first node
that receives a request is called an initial node. The initial node parses the request and
determines whether to service it by itself or forward it to another node (called service
node) based on the cache locality and load balance information. The request is handled
by the initial node when the requested file is cached in the initial node, or the file is
requested for the first time and no node in the cluster has the cached copy. Otherwise,
the request is forwarded to the remote node, which has a cached copy. The design of
PRESS is based on the fact that reading a file from a remote cache is more efficient than
reading it from a local disk. Then, the service node sends the response to the initial
node, using the backend forwarding scheme [13], which in turn forwards it to the client.
A logical diagram of a single PRESS node is shown in Figure 3.1. The main
thread starts a TCP connection with the client. If the request is a local cache hit, the
main thread reads the file from the local cache. If the request needs to be served from the
local disk, the main thread gives the request to a helper thread. Helper threads are used
for disk access to avoid stalling the main thread [59]. In order to communicate within
the cluster, there are two threads (send and receive threads), responsible for sending and












  

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