GZip in PostgreSQL

I love PostgreSQL extensions.

Extensions are the truest expression of the second principle of the original “design of Postgres” vision, to

provide user extendibility for data types, operators and access methods.

Extensions allow users to do more with PostgreSQL than just basic storage and retrieval. PostgreSQL is a full-on integration environment, like Python or Perl, and you can build very complete data manipulation pipelines very close to the metal using native and extension features of PostgreSQL.

Even though I’m a contributor to one of the largest PostgreSQL extensions, I have particularly come to love small extensions, that do one simple thing, particularly one simple thing we maybe take for granted in other environments.

My old HTTP extension is just a binding of libcurl to a SQL interface, so users can do web queries inside the SQL environment.

And today I’ve finished up a GZIP extension, that is just a binding of zlib to SQL, so that users can… compress and decompress things.

It’s not a lot, but it’s a little.

The GZIP entension came about because of an email on the PostGIS development list, where Yuri noted

The amazing ST_AsMVT() has two common usage patterns: copy resulting MVTs to a tile cache (e.g. .mbtiles file or a materialized view), or serve MVT to the users (direct SQL->browser approach). Both patterns still require one additional data processing step – gziping.

Huh. And this use case also applies to people generating GeoJSON directly in the database and sending it out to web clients.

The PostgreSQL core has generally frowned on compression functions at the SQL level, because the database already does compression of over-sized tuples as necessary. The last thing we want is people manually applying compression to column values, and then stuffing them into rows where the database will then have to re-compress them internally. From the perspective of storage efficiency, just standing back and letting PostgreSQL do its work is preferable.

But from the perspective of an integration environment, where an application might be expected to emit or consume compressed data, having a tool in SQL to pack and unpack that data is potentially quite useful.

So I did the tiny binding to zlib and packed it up in an extension.

I hope lots of people find it useful.