Подробно о том, как Causal Consistency реализовано в MongoDB / Михаил Тюленев (MongoDB)

Подробно о том, как Causal Consistency реализовано в MongoDB / Михаил Тюленев (MongoDB)

• 1.
  Implementation of Cluster-wide Causal Consistencyin
• 2.
  - What iscausal consistency - Academics view on Causal Consistency - MongoDB architecture - Causal Consistency building blocks - Making Causal Consistency secure - Making Causal Consistency fast - Making Causal Consistency reliable - Causal consistency for end-users Outline
• 4.
  Client-side properties ofcausal consistency - Read your writes - Writes follow reads - Monotonic reads - Monotonic writes
• 5.
  Implementing with anon causally consistent system - Single server systems are causally consistent - Read and write from the same node - Add an application logic to handle the scenarios that have to be causally consistent
• 7.
  Ordering of Eventsin Distributed System Process P Process Q Process R q2: <C2> = 11 p1 r1: <C3> = 11 q1 <C3> = 0<C1> = 10 <C2> = 10 r2: <C3> = 12 q3
• 8.
  Server-side causal consistency Causalconsistency is a partial order of events in a distributed system. If an event A causes another event B, then causal consistency provides an assurance that each other process of the system observes event A before observing event B. If an event A is not causally related to an event B then they are concurrent.
• 9.
  System’s Architecture
• 10.
  Gossiping clusterTime ClusterTime: {uint64} Timestamp(1495470881,6)
• 11.
  Ticking clusterTime {ts: 6}... {ts: 5} ... {ts: 11} ... insert({x:1}, clusterTime: 4) <clusterTime>: 6 <Wall clock>: 11
• 12.
  Reporting operationTime insert({x:1}) {ts: 11}... {ts: 5} ... {ok:1}, { operationTime: 12} {ts: 12} ... <clusterTime>: 11 <Wall clock>: 11
• 13.
  Waiting for afterClusterTime find({x:1},afterClusterTime: {10}, clusterTime: {15}) {ts: 6} ... {ts: 5} ... {x:1}, { operationTime: {11}} {ts: 11} ...
• 14.
  Breaking clusterTime {ts: Timestamp(1495470881,6), term: 1}, ... {ts: Timestamp(1495470881, 5), term: 1}, ... {Timestamp(0xFFFFFFFF, 0xFFFFFFFF} ... insert({x:1}, clusterTime: {0xFFFFFFFF, 0xFFFFFFFE}) LogicalClock:clusterTime = Timestamp(0xFFFFFFFF, 0xFFFFFFFE)
• 15.
  Protecting clusterTime "$clusterTime" :{ "clusterTime" : Timestamp(1495470881, 5), "signature" : { "hash" : BinData(0,"7olYjQCLtnfORsI9IAhdsftESR4="), "keyId" : NumberLong("6422998367101517844") } }
• 16.
  Protecting against operatorerrors {ts: 6} ... {ts: 5} ... insert({x:1}, clusterTime: 100,000) <clusterTime>: 6 <Wall clock>: 11 {Error}, { operationTime: 6}
• 17.
  Signing a rangeof clusterTime find({x:1}, clusterTime: <val>, signature:<hash>) <timeRange> = <val> | 0x0000’0000’0000’FFFF cache:{ <timeRange>:<hash> }
• 18.
  Use dummy signatures -When the auth is off - When a user has advanceClusterTime privilege
• 19.
  How end userssee it let session=db.getMongo().startSession({causalConsistency: true}) db = session.getDatabase(db.getName());
• 20.
  {checking:100} find({name:”misha”}) afterClusterTime: 15 update({name:”misha” checking:100}) {ok:1} operationTime:15 startSession()
• 21.
  Misha Tyulenev misha@mongodb.com