# Pion — a Redis-compatible memory engine **URL:** \ **Category:** Community Showcase\ **Created:** [October 4, 2026, 3:43pm UTC](https://forum.modular.com/t/pion-a-redis-compatible-memory-engine/3546 "2026-10-04T15:43:03Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Pion](https://sea1.discourse-cdn.com/flex001/user_avatar/forum.modular.com/pion/32/1319_2.png) [@Pion](https://forum.modular.com/u/Pion)\ **Post date:** [October 4, 2026, 3:43pm UTC](https://forum.modular.com/t/pion-a-redis-compatible-memory-engine/3546/1 "2026-10-04T15:43:03Z")
I’ve been building Pion: a key-value and vector database that speaks the Redis protocol (RESP2/3), written in Mojo from the socket up. Its main job is to be a local model’s memory. It keeps a prompt’s K/V cache across processes and restarts, so mlx-lm skips a long prefill it has already done once. The engine is Apache-2.0. One part is not: the tuned 1536-dim vector-search kernels ship as a free, closed static library. An open reference implementation of the same algorithms is in the repo, and a differential test checks on every release that the two return identical results. `pixi run build-open` builds everything from source; vector search at 1536 dims is 22–34% slower that way, and nothing else changes. I’d rather say that here than have you find it. **Numbers** (M4 Mac mini; the scripts that produce them are in the repo): - Prompt cache, Llama-3.2-1B-4bit with a 2,049-token prefix and a short question: time to first token goes from 1,242 ms cold to 61.9 ms in the same process (20×), and to 73.9 ms (17×) from a separate process over the wire. A shorter prefix saves less: from a separate process, 1.5× at 34 tokens, 4.5× at 268 and 11× at 1,035. - KV on one worker, `valkey-benchmark -P 10`: GET 2.1M and SET 2.2M requests/s. - Vector search (VectorDBBench, 50K OpenAI 1536-d vectors, ef=150): about 9.4K QPS at recall@100 0.960. Most of the code was written by Claude Code working to my direction. Every change goes through the same gate before it’s pushed: about 130 test files, a differential run against a real Redis, and benchmark floors that never move to make a run pass. The gate is no substitute for users, though: nobody but me has used Pion yet, so there may well be a lot of bugs, because the tests only cover what I thought to test. The two compiler bugs below surfaced that way, as a crash that happened only at -O3 and a decode that disagreed with its reference. **Mojo things that might be useful to you:** - a zero-allocation request path: RESP parsed in place, a 32-byte value type with 23-byte inline strings, replies written into a preallocated buffer; - workers as raw pthreads with explicit 16 MB stacks (`parallelize` moved to `max`, and -O0 frames overflowed the default pool stacks); - a Swiss table that probes 16 control bytes per SIMD compare; - SDOT / VNNI / SSE int8 kernels behind one `sdot_int8`, and what it cost when the SSE arm was quietly unsigned-by-signed; - two compiler behaviours worth knowing, with minimal repros in `tools/mojo_repros/`: a pointer into a `stack_allocation` buffer passed to an out-of-line call is emitted as a `tail call`, and at -O3 the caller’s stores into that buffer disappear (filed as [modular/modular#7241](https://github.com/modular/modular/issues/7241), and still there in the October 4 nightly); and an int8 → uint8 → uint64 cast chain that sign-extended (fixed in 1.1, [modular/modular#6935](https://github.com/modular/modular/issues/6935)). Repo: [github.com/pavelhorak/pion](https://github.com/pavelhorak/pion) site: [pion.pavelhorak.com](https://pion.pavelhorak.com) ---
**Author:** ![Caroline](https://sea1.discourse-cdn.com/flex001/user_avatar/forum.modular.com/caroline/32/8_2.png) [@Caroline](https://forum.modular.com/u/Caroline)\ **Post date:** [October 5, 2026, 1:44pm UTC](https://forum.modular.com/t/pion-a-redis-compatible-memory-engine/3546/2 "2026-10-05T13:44:48Z")
Thanks for sharing and welcome to the forum @Pion! Check out the Modular community channel for distribution if you haven’t already: [GitHub - modular/modular-community: A repo to hold community-submitted rattler-build recipes, to make community packages available via the modular-community prefix.dev channel · GitHub](https://github.com/modular/modular-community) ---
**Author:** ![Pion](https://sea1.discourse-cdn.com/flex001/user_avatar/forum.modular.com/pion/32/1319_2.png) [@Pion](https://forum.modular.com/u/Pion)\ **Post date:** [October 6, 2026, 10:48am UTC](https://forum.modular.com/t/pion-a-redis-compatible-memory-engine/3546/3 "2026-10-06T10:48:27Z")
Thanks, Caroline! Done: I’ve submitted a recipe, [modular/modular-community#391](https://github.com/modular/modular-community/issues/391). Once it’s merged, Pion installs with pixi from the community channel.