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Sprite (contd)

Sprite (contd). Sprite process migration Facilitated by the Sprite file system State transfer Swap everything out Send page tables and file descriptors to receiver Demand page process in Only dependencies are communication-related Redirect communication from home WS to receiver.

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Sprite (contd)

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  1. Sprite (contd) • Sprite process migration • Facilitated by the Sprite file system • State transfer • Swap everything out • Send page tables and file descriptors to receiver • Demand page process in • Only dependencies are communication-related • Redirect communication from home WS to receiver CS677: Distributed OS

  2. Code and Process Migration • Motivation • How does migration occur? • Resource migration • Agent-based system • Details of process migration CS677: Distributed OS

  3. Motivation • Key reasons: performance and flexibility • Process migration (aka strong mobility) • Improved system-wide performance – better utilization of system-wide resources • Examples: Condor, DQS • Code migration (aka weak mobility) • Shipment of server code to client – filling forms (reduce communication, no need to pre-link stubs with client) • Ship parts of client application to server instead of data from server to client (e.g., databases) • Improve parallelism – agent-based web searches CS677: Distributed OS

  4. Motivation • Flexibility • Dynamic configuration of distributed system • Clients don’t need preinstalled software – download on demand CS677: Distributed OS

  5. Migration models • Process = code seg + resource seg + execution seg • Weak versus strong mobility • Weak => transferred program starts from initial state • Sender-initiated versus receiver-initiated • Sender-initiated (code is with sender) • Client sending a query to database server • Client should be pre-registered • Receiver-initiated • Java applets • Receiver can be anonymous CS677: Distributed OS

  6. Who executes migrated entity? • Code migration: • Execute in a separate process • [Applets] Execute in target process • Process migration • Remote cloning • Migrate the process CS677: Distributed OS

  7. Models for Code Migration • Alternatives for code migration. CS677: Distributed OS

  8. Do Resources Migrate? • Depends on resource to process binding • By identifier: specific web site, ftp server • By value: Java libraries • By type: printers, local devices • Depends on type of “attachments” • Unattached to any node: data files • Fastened resources (can be moved only at high cost) • Database, web sites • Fixed resources • Local devices, communication end points CS677: Distributed OS

  9. Resource Migration Actions Resource-to machine binding • Actions to be taken with respect to the references to local resources when migrating code to another machine. • GR: establish global system-wide reference • MV: move the resources • CP: copy the resource • RB: rebind process to locally available resource Process-to-resource binding CS677: Distributed OS

  10. Migration in Heterogeneous Systems • Systems can be heterogeneous (different architecture, OS) • Support only weak mobility: recompile code, no run time information • Strong mobility: recompile code segment, transfer execution segment [migration stack] • Virtual machines - interpret source (scripts) or intermediate code [Java] CS677: Distributed OS

  11. Agents • Software agents • Autonomous process capable of reacting to, and initiating changes in its environment, possibly in collaboration • More than a “process” – can act on its own • Mobile agent • Capability to move between machines • Needs support for strong mobility • Example: D’Agents (aka Agent TCL) • Support for heterogeneous systems, uses interpreted languages CS677: Distributed OS

  12. Software Agents in Distributed Systems • Some important properties by which different types of agents can be distinguished. CS677: Distributed OS

  13. Agent Technology • The general model of an agent platform (adapted from [fipa98-mgt]). CS677: Distributed OS

  14. Agent Communication Languages CS677: Distributed OS

  15. Agent Communication Languages • A simple example of a FIPA ACL message sent between two agents using Prolog to express genealogy information. CS677: Distributed OS

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