vibed/nbd/.beans/nbd-oziy--turso-cache-for-list-performance.md

title	status	type	priority	created_at	updated_at
Turso cache for list performance	completed	feature	low	2026-03-10T23:30:30Z	2026-03-10T23:30:30Z

Add a Turso (libsql) cache in .nbd/cache.db to accelerate nbd list and nbd ready for large ticket stores.

Motivation

list_tickets currently does O(n) file reads on every call. For stores with hundreds of tickets this is measurably slow. A Turso/libsql cache avoids re-reading unchanged files by comparing file modification times (mtimes).

Approach

Runtime migration: async-std → tokio

libsql requires tokio. Migrate the entire crate:

• Cargo.toml: remove async-std, add tokio = { version = "1", features = ["full"] } and libsql = "0.6"
• src/main.rs: #[async_std::main] → #[tokio::main], async_std::fs::remove_file → tokio::fs::remove_file
• src/store.rs: use async_std::fs → use tokio::fs, use async_std::prelude::* removed (tokio ReadDir uses .next_entry().await not stream iteration)
• src/tests.rs: #[async_std::test] → #[tokio::test], async_std::fs → tokio::fs

Crate dependency

tokio = { version = "1", features = ["full"] }
libsql = "0.6"

store.rs additions

New async function open_cache(root: &Path) -> Result<libsql::Connection>:

• Opens (or creates) .nbd/cache.db via libsql::Builder::new_local(path).build().await?.connect().
• Runs migration: CREATE TABLE IF NOT EXISTS tickets (id TEXT PRIMARY KEY, json TEXT NOT NULL, mtime INTEGER NOT NULL).

New function list_tickets_cached(root: &Path) -> Result<Vec<Ticket>>:

1. Scan directory for files + mtimes (using tokio::fs::read_dir + metadata).
2. Open cache DB.
3. For each file: query cache for matching (id, mtime); if hit, deserialise from cached JSON; if miss, read file, parse, upsert to DB.
4. Delete DB rows for IDs no longer on disk.
5. Return sorted by priority desc.

Fall back to list_tickets on any cache error.

main.rs

cmd_list, cmd_ready, cmd_next use list_tickets_cached instead of list_tickets.

Files to change

File	Change
Cargo.toml	Replace async-std with tokio, add libsql
src/store.rs	async_std → tokio fs API, add cache functions
src/main.rs	async_std → tokio main/fs
src/tests.rs	async_std → tokio test/fs
tests/integration.rs	Add cache smoke test

Validation

cargo fmt && cargo check && cargo clippy && cargo test
cargo run -- list  # should create .nbd/cache.db on first run
cargo run -- list  # second run uses cache