SPREAD TOOLKIT

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SPREAD TOOLKIT

• High performance messaging middleware
• Presented by
• Sayantam Dey
• Vipin Mehta

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What is SPREAD?

• Spread is a group communication system that
  provides a number of messaging services to
  applications. These services can then be used by
  applications to make it easy to write
  full-featured reliable groupware, distributed
  servers, client-server applications, chat and
  news services, and many other networked enabled
  tools.

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SPREAD How it works

• SPREAD is composed of 2 entities daemons and
  client processes.
• Daemon(s) maintain information about all
  processes connected to it and the presence of
  other daemon(s), if any.
• Client processes join/leave the group or
  send/receive messages using the SPREAD primitives.

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Basic Services

• Abstraction of a group a name represents a set
  of processes, all of whom receive messages sent
  to the group.
• Multicast of messages to a group.
• Membership.
• Reliable message delivery.
• Ordering of messages sent to a group.
• Failure detection of members of group.
• A strong semantic model of how messages are
  handled in response to group changes.

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SPREAD primitives

• SP_connect() Initial call an application must
  make to establish a connection with a Spread
  daemon.
• SP_disconnect() Called when the application is
  finished with a connection to the Spread daemon.
• SP_join() Joins a group with the name passed as
  the string group. If the group does not exist
  among the Spread daemons it is created, otherwise
  the existing group with that name is joined.
• SP_leave() Leaves a group with the name passed
  as the string group.
• SP_multicast and family SP multicast and its
  variants all can send a message to one or more
  groups.
• SP_receive and SP_scat_receive This receives
  data and membership messages.
• Other functions for error reporting.

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SPREAD architecture

• Modular Design. Divided into 2 components
  implementation of the network communication layer
  and multiple client interfaces.
• Multiple link protocols supported in the network
  communication layer. Currently implements 3.
• Ring Protocol for low latency LANs with not more
  than 30 daemons.
• Point to Point stable transport over WAN.
• Hop cross WAN with high latency and loss.
• Interfaces implemented in C, Perl and Java.

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SPREAD guarantees

• Native support of Extended Virtual Synchrony
  (EVS).
• Can detect network partition. Generates a
  NETWORK event, which allows client processes to
  obtain the updated membership view.
• Provides a Level of Service.
• This value determines the extent of ordering and
  reliability of the message. The application can
  choose different levels for each message.
• 5 different levels of service implemented.

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SPREAD guarantees continued

• This table shows the different levels of service
  and their relationship with ordering and
  reliability. (from the SPREAD toolkit users
  guide)

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SPREAD application areas

• Replicated servers
• Generic message bus for clusters and distributed
  clusters
• N-way fail-over for IP addresses
• Collaborative tools share data, video and audio
  conferencing
• Distributed Shared Memory

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Why use SPREAD

• Powerful, but simple API. Only six basic calls
  are required to utilize Spread.
• Spread is optimized and can handle over 8,000
  1Kbytes messages a second in local area network
  settings.
• Spread allows unicast, multicast, multi-group
  multicast, scatter-gather calls, and multiple
  query functions.
• Flexible message semantics Spread supports all
  levels of messaging from unreliable to agreed
  (also known as total order) to safe (which
  guarantees all daemons receive the message before
  any deliver it to applications), and provides
  complete extended virtual synchrony.

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Why use SPREAD continued

• Spread handles network and machine partitions and
  re-merges safely and notifies applications about
  the current state of the group.
• Cross Platform Spread supports cross-platform
  operation between Unix (BSD, Linux, Solaris,
  Irix, AIX, Mac OS X, etc.) and Windows
  (2000/NT/98/95).
• Spread currently has programming API's for C/C,
  C, Java, Perl, Python and Ruby.

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References

• www.spread.org
• www.cnds.jhu.edu
• SPREAD user guide
• The Spread Wide Area Group Communication System,
  Yair Amir and Jonathan Stanton.