Part 3: Clear Idle Rooms

A room nobody uses should forget its messages. Each room has one alarm: a time at which Rivet calls the room again, whether or not anyone else does. Set it on every post, and clear the room when it fires.

Pick the idle time

import { Default } from "./cluster.ts";

const IDLE_MS = 60 * 60 * 1000;

Set the alarm on every post

        post: (author: string, text: string) =>
          Effect.gen(function* () {
            yield* (yield* sql.exec(
              "INSERT INTO messages (author, text) VALUES (?, ?)",
              author,
              text,
            )).toArray();
            const now = yield* Effect.sync(() => Date.now());
            yield* state.storage.setAlarm(now + IDLE_MS);
          }),

setAlarm takes a time in milliseconds. Setting it again moves it, so the alarm keeps getting pushed back while people talk, and fires an hour after the last post.

Clear the room when it fires

        messages: () =>
          Effect.gen(function* () {
            const rows = yield* sql.exec<{ author: string; text: string }>(
              "SELECT author, text FROM messages",
            );
            return yield* rows.toArray();
          }),
        alarm: () =>
          Effect.gen(function* () {
            yield* (yield* sql.exec("DELETE FROM messages")).toArray();
          }),
      };

alarm isn’t a method callers can run. Rivet calls it when the alarm comes due.

Deploy

pnpm alchemy deploy

bun alchemy deploy

npx alchemy deploy

yarn alchemy deploy

Post a message, then read it back an hour later. The list is empty. The visitor count stays, because it lives in key-value storage, not in the table.

You have rooms that keep a conversation while people talk, and forget it when they leave.