Comment by saisrirampur | Hacker News Reader

Comment by saisrirampur | Hacker News Reader

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Great question! If you’re starting a greenfield application, pg_clickhouse makes a lot of sense since you’ll be using a unified query layer for your application.

Now, coming to your question about replication: you can use PeerDB (acquired by ClickHouse https://github.com/PeerDB-io/peerdb), which is laser-focused and battle-tested at scale for Postgres-to-ClickHouse replication. Once the data is replicated into ClickHouse, you can start querying those tables from within Postgres using pg_clickhouse. In ClickHouse Cloud, we offer ClickPipes for Postgres CDC/replication, which is a managed service version of PeerDB and is tightly integrated with ClickHouse. Now there could be non-transcational tables that you can directly ingest to ClickHouse and still query using pg_clickhouse.

So TL;DR: Postgres for OLTP; ClickHouse for OLAP; PeerDB/ClickPipes for data replication; pg_clickhouse as the unified query layer. We are actively working on making this entire stack tightly integrated so that building real-time apps becomes seamless. More on that soon! :)

Nice! Right now I'm using Timescaledb, do you think it makes sense to move to a Postgres+CH setup instead? or only if I hit the limit of timescaledb?

Also what would be the benefit for me of querying clickhouse from Postgres, rather than directly through my backend via an ORM/SDK? is that because it would allow me to do JOINs?

What would be the typical setup if I want to JOIN analytical data (eg my IoT device readings) from CH with some business data (eg the user owning the device) from my Postgres? Would I replicate that business data to CH to do the join there, or would that be typically the exact use-case for pg_clickhouse?

Great questions! ClickHouse is a purpose-built analytical database with thousands of optimizations for analytics, which is why it’s typically faster and more scalable than TimescaleDB. Here’s a post that covers real scenarios where users have moved workloads from Timescale to ClickHouse: https://clickhouse.com/blog/timescale-to-clickhouse-clickpip...

If your operational (OLTP) tables are reasonably big, the recommended approach is to replicate them into ClickHouse and let ClickHouse handle the joins. This avoids cross-database joins and lets the execution be pushed fully into ClickHouse. You can use ClickPipes/PeerDB to make that super easy. https://clickhouse.com/docs/integrations/clickpipes/postgres... https://clickhouse.com/docs/integrations/clickpipes/postgres

Where pg_clickhouse fits: If you’re already using Postgres for OLTP and want to offload analytics to ClickHouse without rewriting your app, the pg_clickhouse extension helps. It lets you run OLTP and OLAP queries from Postgres, while pushing the analytical queries—and their joins—down to ClickHouse, where the replicated data lives. Going native i.e. querying ClickHouse directly for OLAP will be the most optimal and is recommended if your analytics is advanced/complex. We will be evolving pg_clickhouse over the coming months to support pushdown for more and more complex/advanced queries :)

Very interesting! So right now I'm developing the backend, so I can still move analytics to CH, but I'm still wondering whether it would make sense because it might not be so large that it requires it (eg 50G/year of data I'd say)

And on the other hand, I can imagine that there could be plenty of footguns with replication to another database (not instant, what about schema changes, backfills, what if some database is shutdown for update while replicating, etc), so I'm a bit cautious about having a complex setup right now

Would you have some basic examples of a "mini-backend" Postgres+Clickhouse replication, using docker-compose + Typescript/Python or something, so I could play with it and take a look at what could be the operational complexity?

You should just give it a shot in 10-15 min and see how it looks with ClickHouse. We made it that simple with ClickPipes :). Don’t intend to sell here, but it is as simple as signing up for trial on ClickHouse Cloud and clicking a few buttons and start seeing PG data getting synced.

In regards to footguns with replication, totally understand you being cautious. Last 2 years at PeerDB/ClickPipes was laser focused on just Postgres CDC to provide a dead simple yet highly reliable experience. The product has 100s of features, addresses 100s of footguns and actively being enhanced. Sharing some customers using this production https://clickhouse.com/blog/postgres-cdc-year-in-review-2025... You should give it a shot to see how easy it is. :)

In regards to sample apication, here is one, https://github.com/ClickHouse/HouseClick It showcases PG + CH stack. We just merged a PR to integrate pg_clickhouse too. The good news is that, there is a blog planned in a couple of weeks which showcases a tightly integrated experience PG +CH with CDC and pg_clickhouse, all in OSS. It will have docker-compose too. Your question adds up to what we are thinking next, I couldn’t resist myself to reveal it. ;) :)

Nice! Looking forward to reading it!

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