Skip to content

replication.md

Latest commit

 

History

History
116 lines (84 loc) · 2.96 KB

replication.md

File metadata and controls

116 lines (84 loc) · 2.96 KB

Replication: Current Flow and Testing

How replication works right now

  1. Server role selection on startup.
  • cmd/server/main.go reads args.
  • Default role is master.
  • If started with --replicaof <host> <port>, role becomes slave.
  1. Replica initiates connection to master.
  • In slave mode, go helper.ConnectToMaster(st) is started.
  • Replica dials masterHost:masterPort.
  1. Replica performs handshake on the same TCP connection.
  • Sends PING.
  • Sends REPLCONF listening-port <replica-port>.
  • Sends REPLCONF capa psync2.
  • Sends PSYNC ? -1.
  1. Master handles PSYNC and registers replica connection.
  • On PSYNC, master sends +FULLRESYNC <replid> <offset>.
  • Sends an RDB bulk payload (currently emptyRDB).
  • Appends that same conn into st.Replicas.
  1. Replica reads snapshot then enters stream loop.
  • Reads FULLRESYNC line.
  • Reads RDB bulk header and exact binary payload.
  • Enters loop reading RESP arrays from the master connection.
  • Applies incoming commands via commands.ApplyReplicaCommand(st, parts).
  1. Master propagates commands to registered replicas.
  • After command execution in normal request flow, master calls helper.PropagateToReplicas(st, parts).
  • PropagateToReplicas serializes the command to RESP and writes to each st.Replicas socket.
  1. Effective replicated command support today.
  • Replica apply path currently handles only SET.
  • Other propagated commands are ignored by ApplyReplicaCommand.

Important current limitations

  • master_repl_offset is not incremented during propagation.
  • Dead/disconnected replica sockets are not removed when writes fail.
  • Replica command apply is limited (currently only SET).

Manual test steps

1) Build

go build -o go_redis_server ./cmd/server

2) Start master (Terminal A)

./go_redis_server --port 6380

3) Start replica (Terminal B)

./go_redis_server --port 6381 --replicaof 127.0.0.1 6380

4) Write on master (Terminal C)

redis-cli -p 6380 SET mykey hello
redis-cli -p 6380 GET mykey

Expected:

  • Master returns OK for SET and hello for GET.

5) Read on replica

redis-cli -p 6381 GET mykey

Expected:

  • Replica returns hello.

6) Verify replication role reporting

redis-cli -p 6380 INFO replication
redis-cli -p 6381 INFO replication

Expected:

  • Master info contains role:master.
  • Replica info contains role:slave.

7) Show current command-coverage gap (INCR example)

redis-cli -p 6380 SET c 1
redis-cli -p 6380 INCR c
redis-cli -p 6380 GET c
redis-cli -p 6381 GET c

Expected right now:

  • Master GET c is 2.
  • Replica GET c may still be 1 because replica apply path currently handles only SET.

8) Optional raw RESP test (if redis-cli is unavailable)

printf '*3\r\n$3\r\nSET\r\n$5\r\nmykey\r\n$5\r\nhello\r\n' | nc 127.0.0.1 6380
printf '*2\r\n$3\r\nGET\r\n$5\r\nmykey\r\n' | nc 127.0.0.1 6381

Expected:

  • Replica returns hello for mykey.