WalShadow: Sub-second Postgres replication to ClickHouse from physical WAL
Summary
WalShadow is an open-source engine that replicates Postgres data to ClickHouse directly from physical WAL, bypassing logical replication. It decodes WAL outside the source and writes ClickHouse-native blocks, enabling near-physical standby latency with analytics-ready data. The architecture includes tracking live schema, parallel decoding, building ClickHouse blocks, and parallel inserts, with ordering preserved via WAL positions. Benchmarks show around 200 ms commit-to-visible latency and ~289k rows/second throughput, with private preview available for ClickHouse Managed Postgres.