Module replicas 

D1 read replicas: reads go to a nearby copy of the database, writes to the primary, and each visitor still reads what they wrote (Rails’ automatic role switching, without a second database to configure).

Turn it on in two places:

1. enable read replication on the database (Cloudflare dashboard, D1, Settings), free on every plan;
2. set the Worker variable D1_REPLICAS to on (D1_REPLICAS: bindings.text("on") in cloudflare.config.ts).

Each request handled by serve then queries its databases through one D1 session: a GET or HEAD may start on any replica, other methods start on the primary, and later statements of the request see the earlier ones. After a request that wrote, the response sets a short-lived cookie holding the session’s bookmark (ocre_d1_<binding>, 5 minutes); the visitor’s next requests resume from it, so a page shown after a form never misses the new row. Responses of read-only requests set no cookie and stay cacheable.

Jobs, cron runs and email handlers query the primary. Without the variable, or with replication off on the database, queries behave as before: sessions reach the primary.

Free plan

No extra cost: replication and sessions are free, and a replica answers reads that would otherwise cross the world to the primary.

Examples

assert_eq!(ocre::replicas::REPLICAS_VAR, "D1_REPLICAS");

Constants

REPLICAS_VAR

Worker variable turning replicas on when set to on: D1_REPLICAS.