WalShadow: Sub-second Postgres replication to ClickHouse from physical WAL

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WalShadow replicates Postgres data directly from physical WAL into ClickHouse, delivering around 200 ms latency and 289,000 rows per second in benchmarks.

Opening excerpt

-> Scroll to top <- Back Blog / Product Copy page Copied! More actions View as Markdown Open this page in Markdown Open in ChatGPT Ask questions about this page Open in Claude Ask questions about this page Open in v0 Ask questions about this page Introducing WalShadow: Sub-second Postgres replication to ClickHouse from physical WAL Sai Srirampur Sep 10, 2026 · 7 minutes read Today, we’re announcing WalShadow , an open-source engine that replicates Postgres data to ClickHouse directly from physical WAL.

In our benchmarks, transactions committed in Postgres became visible in ClickHouse in around 200 ms, while WalShadow sustained 289K rows/sec, effectively keeping pace with the source Postgres instance.

Unlike traditional CDC based systems, WalShadow doesn’t use Postgres logical replication. It consumes the same physical WAL stream used by Postgres replicas, decodes it outside the source database, and writes ClickHouse-native blocks directly into ClickHouse.

WalShadow supports the complete replication lifecycle, including initial load, continuous replication, schema evolution, restart …

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