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Databases & messaging · #clickhouse
Goal Upgrade a small Java application’s ClickHouse schema without service interruption. The application uses the official JDBC driver and a ReplicatedMergeTree table that must stay writable during the change. Constraints ALTER TABLE ADD COLUMN with a default value temporarily locks writes on the shard. Drop‑and‑swap requires a brief window where the old tabl
ClickHouse manages server-side connection limits through the max_connections setting, while the HTTP interface relies on the Connection: keep-alive header and keep_alive_timeout to maintain persistent sessions. In single-node environments, this mechanism handles basic connection reuse effectively. As deployments scale to distributed clusters, relying on inte
Schema Update Propagation in ReplicatedMergeTree When executing ALTER TABLE ... UPDATE or similar mutations on a ReplicatedMergeTree table across a cluster, ClickHouse manages these changes asynchronously by default. The metadata is propagated via ZooKeeper, but the actual data rewriting occurs in the background as parts are merged. In environments requiring