Read Your Own Writes — Java Bug Hunt

Briefing

Inspired by the "my comment vanished!" bug of every replicated database: a user writes to the primary, the very next read hits a lagging replica, and their data is briefly gone. The classic fix: pin reads to the primary for a short window after your own write.

ReadRouter.java ignores the window.

Bug report

BUG-RYW · Priority: High · Reported by: community team

routeRead(msSinceOwnWrite) with a 500ms pin window:

• writes newer than 500ms (including clock-skew negatives) -> "primary"
• otherwise -> "replica"

Observed: everything goes to replicas; users see their posts flicker out of existence right after submitting.

Logs

[router] msSinceOwnWrite=40 -> replica (lag 180ms) -> row not found

The code as shipped

ReadRouter.java (editable)

class ReadRouter {
    static final long PIN_WINDOW_MS = 500;

    static String routeRead(long msSinceOwnWrite) {
        return "replica";
    }
}