replication-guide
Installation
SKILL.md
Replication Guide
When to use this skill
Load when users ask about replication setup, lag, failover, or Keeper/ZooKeeper.
ReplicatedMergeTree Basics
- Engine:
ReplicatedMergeTree('/clickhouse/tables/{shard}/{database}/{table}', '{replica}') - Requires ZooKeeper or ClickHouse Keeper
- All replicas are equal — any replica can accept writes
- Replication is asynchronous by default
Monitoring Replication
system.replicas— per-table status:absolute_delay,queue_size,is_leader,is_readonlysystem.replication_queue— pending operations: fetches, merges, mutations- Key health indicators:
absolute_delay = 0— fully caught upis_readonly = 0— accepting writesqueue_size < 10— healthy queueactive_replicas = total_replicas— all replicas online
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