Causal Logging : Manetho Rohit C Fernandes 10/25/01

Manetho System Model Non determinististic events Message Receive Internal event(Kernel call) Creation of a new process Output Commit Stable Storage + Volatile Memory

Manetho properties Tolerate any number of simultaneous failures Low failure-free overhead Only failed processes roll back

Example Manetho Execution

Causal Logging : Intuition Piggyback determinant of non- deterministic event on outgoing messages Determinant? Piggyback Antecedence Graphs

Antecedence Graph Directed acyclic graph Nodes : State Intervals Edges : Happened before(immediate)

Antecedence Graph

Receive Node Two incoming edges Fields Receiver ID Sender ID Index of created state interval Unique identifier of message

Internal Event Node One incoming edge Fields Type of event Replay information

Failure Free Operation Each process maintains AG of its current interval Log that contains data and ID of each message sent Message Send : Piggyback AG of current state interval

Optimization Need not send complete AG Incremental piggybacking AG(  i+1 p ) is a proper subgraph of AG(  i p ) Process q communicates to p max j such that  j p is in q’s AG P sends AG (  i p ) - AG (  j p )

Information on Stable Storage Checkpoints AG (asynchronously) : Need not piggyback part of AG which is in disk Output commit: Save AG to disk

Incarnation Numbers Each process starts a new incarnation after recovery Integer stored in stable storage Tagged on outgoing messages Messages from old incarnations discarded

Recovery Protocol Recover(p,c,INCNUM,S) Step 1 INCNUM  INCNUM+1 ; save INCNUM INCVEC[p]  INCNUM G  AG(  p c ) // stable storage

Recovery Protocol Step 2 For all q  S, q  p (INQ,AGQ)  remote call at q:GET_AG(p) G  G  AGQ INCVEC[q]  INQ For all q  S, q  p Remote call at q: SEND_INC(p,INCVEC)

Recovery Protocol Step 3 m  max j such that  p j  G Recover upto  p m Don’t send out application messages but log them For receive, request message from sender’s log Replay internal event

Recovery Example

Available Antecedence Graphs

Application Characteristics

Performance Overhead

Coordinated vs. Uncoordinated