Each response has fields telling you if it's the primary or a replica handling your request and from

Each response has fields telling you if it's the primary or a replica handling your request and from which region: https://developers.cloudflare.com/d1/best-practices/read-replication/#check-where-d1-request-was-processed

const result = await env.DB.withSession()
  .prepare(`SELECT * FROM Customers WHERE CompanyName = 'Bs Beverages'`)
  .run();
console.log({
  servedByRegion: result.meta.served_by_region ?? "",
  servedByPrimary: result.meta.served_by_primary ?? "",
});

const result = await env.DB.withSession()
  .prepare(`SELECT * FROM Customers WHERE CompanyName = 'Bs Beverages'`)
  .run();
console.log({
  servedByRegion: result.meta.served_by_region ?? "",
  servedByPrimary: result.meta.served_by_primary ?? "",
});

const result = await env.DB.withSession()
  .prepare(`SELECT * FROM Customers WHERE CompanyName = 'Bs Beverages'`)
  .run();
console.log({
  servedByRegion: result.meta.served_by_region ?? "",
  servedByPrimary: result.meta.served_by_primary ?? "",
});

const result = await env.DB.withSession()
  .prepare(`SELECT * FROM Customers WHERE CompanyName = 'Bs Beverages'`)
  .run();
console.log({
  servedByRegion: result.meta.served_by_region ?? "",
  servedByPrimary: result.meta.served_by_primary ?? "",
});

Llambrospetrou Each response has fields telling you if it's the primary or a replica handling y...

lambrospetrouOP•9/7/25, 8:18 AM

Also, I assume you use the Sessions API. Otherwise, all your requests will go to the primary regardless if you have enabled read replication or not.

Llambrospetrou Also, I assume you use the [Sessions API](https://developers.cloudflare.com/d1/b...

aza547•9/7/25, 8:44 AM

Thank you for the detailed response. That clears it up for me

- It would be awesome if this could be captured in the docs.
- My problem is almost certainly that I'm not using the sessions API.

This is not concrete. What is quiet, and what is "still receiving queries from all over"?

What I was trying to convey is that there is consistent non-zero traffic in every region, and that I expected read replicas in every region to be queried. "Quiet" as in "not enough to overload the primary DB".

The docs to me imply that the sessions API is to guarantee sequential consistency for a set of queries, but the bulk of my traffic is pulling a single field out of the database so I don't actually care about sequential consistency in a lot of cases.

Feel free to point out if I'm missing the obvious, but I don't think the docs make it clear that the sessions API is required for queries to hit a read replica.

I'll go add some .withSession().withSession() calls to my worker and see what happens. Thanks again.

Aaza547 Thank you for the detailed response. That clears it up for me 🙂 - It would be a...

lambrospetrouOP•9/7/25, 8:45 AM

At the very top: Your application can use read replicas with D1 Sessions API.Your application can use read replicas with D1 Sessions API.

We can make it even stronger if that's not clear enough. I will add another clarifying sentence there.

aza547•9/7/25, 8:50 AM

That would be great, I guess I'm still reading that as "you can use the sessions API optionally to get sequential consistency which a read replication enabled DB otherwise doesn't provide"

aza547•9/7/25, 9:13 AM

Happy days

OOr Will enabling read replication cause the primary DB to be locked while the repli...

lambrospetrouOP•9/7/25, 9:42 PM

No, replication is done asynchronously, and there is no blocking time while replicas are being created. As I mentioned above though, in order to get benefits from replicas you would need some continuous traffic, especially since 3GB would need a few seconds to boot.
If you only have a request per minute for example, you will pretty much always go to the primary.

flof.fly•9/7/25, 9:56 PM

Is there a way to Duplicate a D1 (including data) via APICall or CLI?

Fflof.fly Is there a way to Duplicate a D1 (including data) via APICall or CLI?

lambrospetrouOP•9/8/25, 7:13 AM

Not at the moment

Pingo•9/8/25, 2:12 PM

Hi im a noob to d1 and my biggest concern is obviously avoiding something like tea app disaster. So I wanted to know if there is an awesome list with projects using d1 so I can learn how real life applications are configuring d1 with battle tested patterns. I am extremely paranoid about managing user data correctly. Sorry if this is not the place to ask about this.

PPingo Hi im a noob to d1 and my biggest concern is obviously avoiding something like t...

lambrospetrouOP•9/8/25, 2:24 PM

Hi im a noob to d1 and my biggest concern is obviously avoiding something like tea app disaster.

What is the "tea app disaster"?

D1 is durable storage, and provides up to 30 days of Point-in-time-restore for your data to be able to revert to any point in these 30 days.

There are certain limits, about storage (10GB) and fixed resource limits due to being single threaded execution of the queries, but we don't lose your data.

If you have specific concerns or questions, happy to answer. Or anyone in this community for what's worth.

Llambrospetrou > Hi im a noob to d1 and my biggest concern is obviously avoiding something like...

Isaac McFadyen•9/8/25, 2:28 PM

What is the "tea app disaster"?

Recent data breach from an app called Tea: https://www.bbc.com/news/articles/c7vl57n74pqo

IIsaac McFadyen > What is the "tea app disaster"? Recent data breach from an app called Tea: htt...

lambrospetrouOP•9/8/25, 2:55 PM

D1 data is encrypted at rest (built ontop of Durable Objects), but obviously access is authenticated using either your worker binding (so having access to deploying workers) or to the Cloudflare access tokens, so you should protect your access tokens as any other secret. I can't say anything specific about the leaked incident of Tea.

Gab•9/8/25, 3:35 PM

HI guys, how can I aapply drizzle migrations to preview or local d1 database?
im trying with ->
wrangler d1 migrations apply d1_database --local
the CLI say it works well, but when I come to sql editor, there is no schema in the database

Gab•9/8/25, 3:38 PM

when I use wrangler d1 migrations apply d1_database --remote
it workers well on the main d1 database, but --local does not seen to apply

GGab when I use wrangler d1 migrations apply d1_database --remote it workers well on ...

Anes•9/8/25, 3:43 PM

you can apply the migrations using drizzle, your drizzle.config.ts should look like this:

import { defineConfig } from "drizzle-kit";
import { config } from "dotenv";

config({
  path: ".env.stage"
});

export default defineConfig({
  schema: ["./src/app/schema.ts", "./src/app/auth-schema.ts"],
  out: "./drizzle/app",
  dialect: "sqlite",
  driver: "d1-http",
  dbCredentials: {
    accountId: process.env.CF_ACCOUNT_ID,
    databaseId: process.env.CF_DATABASE_ID,
    token: process.env.CF_TOKEN,
    url: ""
  }
});

import { defineConfig } from "drizzle-kit";
import { config } from "dotenv";

config({
  path: ".env.stage"
});

export default defineConfig({
  schema: ["./src/app/schema.ts", "./src/app/auth-schema.ts"],
  out: "./drizzle/app",
  dialect: "sqlite",
  driver: "d1-http",
  dbCredentials: {
    accountId: process.env.CF_ACCOUNT_ID,
    databaseId: process.env.CF_DATABASE_ID,
    token: process.env.CF_TOKEN,
    url: ""
  }
});

eg script: "db:push": "drizzle-kit push --config=./drizzle.config.ts""db:push": "drizzle-kit push --config=./drizzle.config.ts",

Gab•9/8/25, 3:48 PM

ok, do i need to change the CF_DATABASE_ID for the local preview d1 database? (i can add in .dev.vars)

Gab•9/8/25, 4:19 PM

I got working with the old script, It was working, thje problem was at my betterAuth objecta tha was not findind the correct db

csmykay•9/8/25, 6:27 PM

Howdy all. Is there a good "best practices" document for working with D1 databases locally with multiple developers and how best to push updates? I actually have a response from Claude but looking for something to double check.