Your "bulk value fetche[r]" is handing out ["unprotected sqlite3_value"](https://www.sqlite.org/c3ref/value.html) objects. (See 3rd paragraph at link.) Per the 4th paragraph, these objects have limited usage in other API's, and those usages, presumably to be made by the multitude of threads you wish to not individually fetch column values anymore, are likely to induce the same sort of mutex locking/unlocking bottleneck you seek to avoid. Maybe if that bulk-fetch was bothering to make copies of values that can auto-magically change form under the covers, that congestion might be avoided, at least at the outset.