Simon Willison’s Weblog

PostgreSQL: nbtree/README (via) The PostgreSQL source tree includes beatifully written README files for different parts of PostgreSQL. Here’s the README for their btree implementation—it continues to be actively maintained (last change was is March) and “git blame” shows that parts of the file date back 25 years, to 1996! # 25th June 2021, 6:09 pm

Hierarchical Structures in PostgreSQL (via) Two techniques I hadn’t seen before: the first is to define a materialized view using a CTE that offers efficient tree queries against a PostgreSQL array of path components (plus a trigger to update the materialized view), the second is with the PostgreSQL ltree extension which ships as part of PostgreSQL and hence should be widely available. # 25th June 2021, 5:19 pm

Multi-region PostgreSQL on Fly (via) Really interesting piece of architectural design from Fly here. Fly can run your application (as a Docker container run using Firecracker) in multiple regions around the world, and they’ve now quietly added PostgreSQL multi-region support. The way it works is that all-but-one region can have a read-only replica, and requests sent to application servers can perform read-only queries against their local region’s replica. If a request needs to execute a SQL update your application code can return a “fly-replay: region=scl” HTTP header and the Fly CDN will transparently replay the request against the region containing the leader database. This also means you can implement tricks like setting a 10s expiring cookie every time the user performs a write, such that their requests in the next 10s will go straight to the leader and avoid them experiencing any replication lag that hasn’t caught up with their latest update. # 17th June 2021, 6:39 pm

Get Started—Materialize. Materialize is a really interesting new database—“a streaming SQL materialized view engine”. It builds materialized views on top of streaming data sources (such as Kafka)—you define the view using a SQL query, then it figures out how to keep that view up-to-date automatically as new data streams in. It speaks the PostgreSQL protocol so you can talk to it using the psql tool or any PostgreSQL client library. The “get started” guide is particularly impressive: it uses a curl stream of the Wikipedia recent changes API, parsed using a regular expression. And it’s written in Rust, so installing it is as easy as downloading and executing a single binary (though I used Homebrew). # 1st June 2020, 10:11 pm

mycli. Really neat auto-complete enabled MySQL terminal client, built using the excellent python-prompt-toolkit. Has a sister-project for PostgreSQL called pgcli. # 11th June 2018, 7:08 pm

Appending the request URL to SQL statements in Django. A clever frame-walking monkey-patch which pulls the most recent HttpRequest object out of the Python stack and adds the current request.path to each SQL query as an SQL comment, so you can see it in debugging tools such as slow query logs and the PostgreSQL “select * from pg_stat_activity” query. # 2nd June 2010, 9:09 am