Transcript Causal logging: Manetho

Causal Logging : Manetho
Rohit C Fernandes
10/25/01
Manetho System Model
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Non determinististic events
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Message Receive
Internal event(Kernel call)
Creation of a new process
Output Commit
Stable Storage + Volatile Memory
Manetho properties
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Tolerate any number of simultaneous
failures
Low failure-free overhead
Only failed processes roll back
Example Manetho Execution
Causal Logging : Intuition
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Piggyback determinant of nondeterministic event on outgoing
messages
Determinant?
Piggyback Antecedence Graphs
Antecedence Graph
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Directed acyclic graph
Nodes : State Intervals
Edges : Happened before(immediate)
Antecedence Graph
Receive Node
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Two incoming edges
Fields
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Receiver ID
Sender ID
Index of created state interval
Unique identifier of message
Internal Event Node
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One incoming edge
Fields
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Type of event
Replay information
Failure Free Operation
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Each process maintains
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AG of its current interval
Log that contains data and ID of each
message sent
Message Send : Piggyback AG of
current state interval
Optimization
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Need not send complete AG
Incremental piggybacking
AG(i+1p) is a proper subgraph of
AG(ip)
Process q communicates to p max j
such that jp is in q’s AG
P sends AG (ip ) - AG (jp )
Information on Stable Storage
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Checkpoints
AG (asynchronously) : Need not
piggyback part of AG which is in disk
Output commit: Save AG to disk
Incarnation Numbers
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Each process starts a new incarnation
after recovery
Integer stored in stable storage
Tagged on outgoing messages
Messages from old incarnations
discarded
Recovery Protocol
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Recover(p,c,INCNUM,S)
Step 1
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INCNUM  INCNUM+1 ; save INCNUM
INCVEC[p] INCNUM
G AG(pc) // stable storage
Recovery Protocol
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Step 2
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For all q  S, qp
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(INQ,AGQ)remote call at q:GET_AG(p)
GGAGQ
INCVEC[q]INQ
For all q  S, qp
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Remote call at q: SEND_INC(p,INCVEC)
Recovery Protocol
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Step 3
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mmax j such that pj  G
Recover upto pm
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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