> "Multiple Readers and Writers in File System Access API" aka `readwrite-unsafe` in v121 (stable in 2 weeks) which could help improve SQLite's performance even more.
As your EDIT notes, Roy (wa-sqlite) has already experimented with this and reports great results. Experimenting with this in the sqlite project's own OPFS VFS (see https://sqlite.org/wasm) is pending, but the feature is not yet widespread enough to replace the current VFSes. We've no information on how long it will take for the other browsers to catch up with that API. Until then, the sqlite project offers two OPFS VFSes, one of which trades speed for a moderate degree of cross-tab concurrency and another which offers tremendous speed but a complete lack of concurrency.
As your EDIT notes, Roy (wa-sqlite) has already experimented with this and reports great results. Experimenting with this in the sqlite project's own OPFS VFS (see https://sqlite.org/wasm) is pending, but the feature is not yet widespread enough to replace the current VFSes. We've no information on how long it will take for the other browsers to catch up with that API. Until then, the sqlite project offers two OPFS VFSes, one of which trades speed for a moderate degree of cross-tab concurrency and another which offers tremendous speed but a complete lack of concurrency.