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Comment by archi42 | Hacker News Reader

The general optimization is actually not that novel: A DBMS might do that for parts of a query. At least in a high performance database lecture this was taught as a possible optimization. Edit: I'd intuitively expect the improvements to be more than 5%< though.

E.g. PostgreSQL can do that these days (not sure if it did back then): https://www.postgresql.org/docs/current/jit-reason.html

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I have had a lot of "fun" with this feature in the past. It has earned a permanent place in my setup script:

ALTER SYSTEM SET jit=off;

Basically a performance blackhole for more complex queries. Most OSM related projects disable it straight away as it only creates headaches.

https://github.com/osm-search/Nominatim/pull/2559 https://github.com/gravitystorm/openstreetmap-carto/blob/mas...

I have been JIT-ing query predicates in database-like systems for over a decade, and some commercial databases have supported it a lot longer than that. There are a couple relevant aspects that impact the performance benefit.

The performance gains are much higher if the database engine was designed to have JIT-ed execution from day one. Grafting it onto a database engine after the fact, like Postgres, is going to gain substantially less benefit than is theoretically possible. Additionally, it mostly benefits databases where query predicates have a large amount of data to process, it doesn’t do much for OLTP. But in the right system and context, large integer factor performance improvements are routinely achievable.

Yes, this is a thing. But the key difference there is... that's being done ... in user space.

We live in a world where just last week Google turned off io_uring access on a pile of machines, and that's only "executing" restricted sets of operations. Executable code in kernel = big giant target painted on back.

Ah, yes, that's an excellent point. Because someone else talked about 5% performance I looked at it with my performance hat on, not the security hat. OTOH we have BPFilter with its VM.

FWIW, the IBM mainframes have channel control programs, which as I understand it, can dynamically generate small programs and send them to the channel controller to execute; can include branching / conditionals also. https://en.wikipedia.org/wiki/Execute_Channel_Program

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