Pg_lake: Postgres with Iceberg and data lake access

Boils down to design decisions; see: https://news.ycombinator.com/item?id=45813631

DuckLake is pretty cool, and we obviously love everything the DuckDB is doing. It's what made pg_lake possible, and what motivated part of our team to step away from Microsoft/Citus.

DuckLake can do things that pg_lake cannot do with Iceberg, and DuckDB can do things Postgres absolutely can't (e.g. query data frames). On the other hand, Postgres can do a lot of things that DuckDB cannot do. For instance, it can handle >100k single row inserts/sec.

Transactions don't come for free. Embedding the engine in the catalog rather than the catalog in the engine enables transactions across analytical and operational tables. That way you can do a very high rate of writes in a heap table, and transactionally move data into an Iceberg table.

Postgres also has a more natural persistence & continuous processing story, so you can set up pg_cron jobs and use PL/pgSQL (with heap tables for bookkeeping) to do orchestration.

There's also the interoperability aspect of Iceberg being supported by other query engines.

i have so desperately wanted to love and use ducklake, but have come across some issues with it in practice (pg catalog). they seem to have to do with maintenance activities and ducklake suddenly throwing http/400 errors on files it created. i’m not sure if it’s due to my write patterns (gather data from sources into a polars dataframe and insert into the ducklake table from the df) into the partitioned tables or something else.

it’s ok in dev/test and for me as the person in the team who’s enamored with duckdb, but it’s made the team experience challenging and so i’ve just kinda reverted to hive partitioned parquet files with a duckdb file that has views created on top of the parquet. attach that file as read only and query away.

i may work up a full example to submit as an issue but up until now too may other things are dominating my time.

Honestly. Just pay snowflake for the amazing DB and ecosystem it is. And then go build cool stuff unless your value add to customers is infra let them handle all that.

> Maybe an example of a problem this solves.

Some service writes a lot of data in parquet files stored on S3 (e.g. logs), and now you want that data to be queryable from your application as if it was in postgres (e.g. near real-time analytics dashboard). pg_lake allows you to load these parquet files into postgres and query the data. You can also join that data with existing tables in postgres.

The point about a datalake is to separate computer and storage. Postgres isn’t a compute layer it’s an access layer.

Your compute asks Postgres “what is the current data for these keys?” Or “what was the current data as of two weeks ago for these keys?” And your compute will then download and aggregate your analytics query directly from the parquet files.

It's not going to scale as well as Snowflake, but it gets you into an Iceberg ecosystem which Snowflake can ingest and process at scale. Analytical data systems are typically trending to heterogenous compute with a shared storage backend -- you have large, autoscaling systems to process the raw data down to something that is usable by a smaller, cheaper query engine supporting UIs/services.

One thing I admire about Snowflake is a real commitment to self-cannibalization. They were super out front with Iceberg even though it could disrupt them, because that's what customers were asking for and they're willing to bet they'll figure out how to make money in that new world

Video of their SVP of Product talking about it here: https://youtu.be/PERZMGLhnF8?si=DjS_OgbNeDpvLA04&t=1195

It'll probably be really difficult to set up.

If it's anything like super base, your question the existence of God when trying to get it to work properly.

You pay them to make it work right.

When we first developed pg_lake at Crunchy Data and defined GTM we considered whether it could be a Snowflake competitor, but we quickly realised that did not make sense.

Data platforms like Snowflake are built as a central place to collect your organisation's data, do governance, large scale analytics, AI model training and inference, share data within and across orgs, build and deploy data products, etc. These are not jobs for a Postgres server.

Pg_lake foremost targets Postgres users who currently need complex ETL pipelines to get data in and out of Postgres, and accidental Postgres data warehouses where you ended up overloading your server with slow analytical queries, but you still want to keep using Postgres.

(1) We've thought about it, no current plans. We'd ideally reimplement DuckLake in Postgres directly such that we can preserve Postgres transaction boundaries, rather than reuse the Ducklake implementation that would run in a separate process. The double-edged sword is that there's a bunch of complexity around things like inlined data and passing the inlined data into DuckDB at query time, though if we can do that then you can get pretty high transaction performance.

(2) In principle, it's a bit easier for pg_duckdb to reuse the existing Ducklake implementation because DuckDB sits in every Postgres process and they can call into each other, but we feel that architecture is less appropriate in terms resource management and stability.

You could say

With DuckLake, the query frontend and query engine are DuckDB, and Postgres is used as a catalog in the background.

With pg_lake, the query frontend and catalog are Postgres, and DuckDB is used as a query engine in the background.

Of course, they also use different table formats (though similar in data layer) with different pros and cons, and the query frontends differ in significant ways.

An interesting thing about pg_lake is that it is effectively standalone, no external catalog required. You can point Spark et al. directly to Postgres with pg_lake by using the Iceberg JDBC driver.

You create foreign tables in postgres using either the pg_lake_table wrapper or pg_lake_iceberg.

Once those tables exist, queries against them are able to either push down entirely to the remote tables and uses a Custom Scan to execute and pull results back into postgres, or we transform/extract the pieces that can be executed remotely using a FDW and then treat it as a tuple source.

In both cases, the user does not need to know any of the details and just runs queries inside postgres as they always have.

110% this!

We have some level of external iceberg table read-only support, but it is limited at the moment. See this example/caveat: https://github.com/Snowflake-Labs/pg_lake/blob/main/docs/fil...

You can use it as a read layer for for specific metadata JSON URL or a table in a REST catalog. The latter got merged quite recently, not yet in docs.

Hypertables definitely had the arrays columns auto-expanding with the custom node type. Not sure what else it would look like for what you describe.

That said, don't sleep on the "this is awesome" parts in this project... my personal favorite is the automatic schema detection:

``` CREATE TABLE my_iceberg_table () USING iceberg WITH (definition_from = 's3://bucket/source_data.parquet'); ```

I want MPP HTAP where SQL inserts/COPYs store data in three(!) formats: - row-based (low latency insert, fast row-based indexed query for single-row OLTP) - columnar-based (slow inserts/updates, fast aggregates/projections) - iceberg-columnar-based (better OLAP price/performance and less lockin than native columnar) And for SELECTs the query engine picks which storage engine satisfies the query using some SQL extension like DB2 "WAITFORDATA" or TiDB @@tidb_read_staleness or MemSQL columnstore_latency and/or similar signalling for performance-vs-cost preference.

And a common permissioning/datasharing layer so I can share data to external and internal parties who can in turn bring their own compute to make their own latency choices.

Ong yes it works this would have made my past job so much easier.

Yes, just COPY table TO 's3://mybucket/data.parquet'

Or COPY table TO STDOUT WITH (format 'parquet') if you need it on the client side.

Also, any planned support for more catalogs?

Hi, what types are you expecting to see that aren't supported? I believe we had support for most/all builtin postgres types.

there's also plenty of other options for warehouse/compute processing of iceberg data storage.

I think this is a pretty big deal, though.

Snowflake does a lot more, though, especially around sharing data across company boundaries.

I gave a talk on that at Data Council, then still discussing the pg_lake extensions as part of Crunchy Data Warehouse.

https://youtu.be/HZArjlMB6W4?si=BWEfGjMaeVytW8M1

Also, nicer recording from POSETTE: https://youtu.be/tpq4nfEoioE?si=Qkmj8o990vkeRkUa

It comes down to the trade-offs made by operational and analytical query engines being fundamentally different at every level.

DuckDB provided a lot of infrastructure for reading/writing parquet files and other common formats here. It also was inherently multi-threaded and supported being embedded in a larger program (similar to sqllite), so made it a good basis for something that could work outside of the traditional process model of Postgres.

Additionally, the postgres extension system supports most of the current project, so wouldn't say it was forced in this case, it was a design decision. :)

One usecase we have (we built it ourselves) is to periodically offload data from Postgres to lake house partitioned data on GCS. The way I see it this can now be done with a single query. Another one is the other way around to use posters as a query engine or to merge offloaded data with your live data.

Hi, one of the developers here. You define credentials that can access the S3 buckets and use those as DuckDB secrets, usually in an init script for pgduck_server. (You can see some examples of this in the testing framework.)

I'll see if we can improve the docs or highlight that part better, if it is already documented—we did move some things around prior to release.

There are Postgres roles for read/write access to the S3 object that DuckDB has access to. Those roles can create tables from specific files or at specific locations, and can then assign more fine-grained privileges to other Postgres roles (e.g. read access on a specific view or table).

It's the same team and same project :). Crunchy Data was acquired by Snowflake.

from the README:

> This separation also avoids the threading and memory-safety limitations that would arise from embedding DuckDB directly inside the Postgres process, which is designed around process isolation rather than multi-threaded execution. Moreover, it lets us interact with the query engine directly by connecting to it using standard Postgres clients.

The README explains it:

> This separation also avoids the threading and memory-safety limitations that would arise from embedding DuckDB directly inside the Postgres process, which is designed around process isolation rather than multi-threaded execution. Moreover, it lets us interact with the query engine directly by connecting to it using standard Postgres clients.

What has been pointed out from the README; also:

- Separation of concerns, since with a single external process we can share object store caches without complicated locking dances between multiple processes. - Memory limits are easier to reason about with a single external process. - Postgres backends end up being more robust, as you can restart the pgduck_server process separately.