# PG Cluster - Replication lag

**URL:** <https://community.fly.io/t/pg-cluster-replication-lag/2627>\
**Category:** Questions / Help\
**Created:** [September 23, 2021, 10:57pm UTC](https://community.fly.io/t/pg-cluster-replication-lag/2627 "2021-09-23T22:57:38Z")\
**Posts on this page:** 1\
**Showing post:** 3

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**Author:** ![fedeotaran](https://sea1.discourse-cdn.com/fly1/user_avatar/community.fly.io/fedeotaran/32/51116_2.png) [@fedeotaran](https://community.fly.io/u/fedeotaran)\
**Post date:** [September 24, 2021, 2:48pm UTC](https://community.fly.io/t/pg-cluster-replication-lag/2627/3 "2021-09-24T14:48:01Z")

</div>

Thanks for the answer!

The strategy we used was to create 2 ecto repo, one for the leader (read / write) and one for the replicas (read only). If the node is in the same region as the leader, both repositories will have the same database url.

The configuration looks:

```auto
fly ssh console -s -a shy-rain-1653
? Select instance: gru.shy-rain-1653.internal
Connecting to [fdaa:0:332b:a7b:1f60:5836:bb9a:2]... complete
/ # /app/bin/brandkit remote
Erlang/OTP 24 [erts-12.0.2] [source] [64-bit] [smp:1:1] [ds:1:1:10] [async-threads:1] [jit:no-native-stack]

Interactive Elixir (1.12.1) - press Ctrl+C to exit (type h() ENTER for help)
iex(shy-rain-1653@fdaa:0:332b:a7b:1f60:5836:bb9a:2)1> Application.get_env(:brandkit, Brandkit.Repo)
[
  url: "postgres://xxx:xxx@brandkit-pg-st.internal:5432/shy_rain_1653?sslmode=disable",
  socket_options: [:inet6],
  pool_size: 10
]
iex(shy-rain-1653@fdaa:0:332b:a7b:1f60:5836:bb9a:2)2> Application.get_env(:brandkit, Brandkit.RepoReadOnly)
[
  url: "postgres://xxx:xxx@gru.brandkit-pg-st.internal:5432/shy_rain_1653?sslmode=disable",
  socket_options: [:inet6],
  pool_size: 10
]
iex(shy-rain-1653@fdaa:0:332b:a7b:1f60:5836:bb9a:2)3>

```

We explicitly use this RepoReadOnly in some queries. We do not all migrate for now.

I followed that post [High Availability & Global Replication · Fly Docs](https://fly.io/docs/getting-started/multi-region-databases/#connect-to-regional-replicas) and took some ideas from this [Multi region database guide](https://community.fly.io/t/multi-region-database-guide/1600) discussion.

The difference in the time of the requests is big.

```auto
GRU (using replica and leader)
app[33dcfef1] gru [info] 19:37:29.017 request_id=FqWzLO6dfiNa7ZoAAAXh [info] Sent 200 in 3462ms

```

```auto
IAD (using leader)
app[2e575cad] iad [info] 19:51:03.302 request_id=FqWz60zLOpGGZIIAAAbh [info] Sent 200 in 122ms

```

These requests only have read operations, but they use both repo.

> [@kurt](#):
>
> We’ll have a hex package to automate what you need in Elixir soon.

We’re sure that our actual configuration is not the best, so it’s going to be awesome! 🙂

We will continue testing, we just want to share our experience and try to better understand how is the correct way to use our PG cluster.

Thanks! 😃

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_[View the full topic](https://community.fly.io/t/pg-cluster-replication-lag/2627)._