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Postgres output plugin for replicating data to Turso.

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⚠️ This project is now deprecated and no longer supported ⚠️

<a href="https://turso.tech">Turso</a> makes it easy to create thousands of databases using the CLI and Platform API.

---

# pg_turso

Postgres [output plugin](https://www.postgresql.org/docs/current/logicaldecoding-output-plugin.html) for replicating data to Turso.

## Status

Replicating tables and views is more or less supported, but:
1. Only basic types - integers and text - were tested. Postgres has way more types, and they may prove problematic to replicate. We can probably just cast them to generic binary blobs and replicate them in that form.

## Installation

This guide assumes that you have a local installation of Postgres. Get one from https://www.postgresql.org/download/

Please note that you need to download zig development version 2023-06-20 or higher: https://ziglang.org/download/

```sh
cd /tmp
git clone https://github.com/turso-extended/pg_turso.git
cd pg_turso
export ZIG=<path where zig executable is>
make
make install # may need sudo
```

## Getting Started 
Let's assume that you have the following table and materialized view that you wish to replicate to the edge with Turso:
```sql
CREATE TABLE IF NOT EXISTS menu(
 dish_id int PRIMARY KEY,
 name text,
 price float
);
CREATE MATERIALIZED VIEW assorted_collection_of_dirt_cheap_dishes
 AS SELECT dish_id, name FROM menu WHERE price <= 2.99;
```

The Turso table corresponding to our materialized view will be automatically created by the plugin, and is going to look more or less as follows:
```sql
CREATE TABLE assorted_collection_of_dirt_cheap_dishes(
   dish_id int PRIMARY KEY ON CONFLICT REPLACE,
   name
);
```

The way replication plugins work is as follows.

First, you need to change your "wal level" to `logical`. Logical WAL means that WAL entries can be parsed
and structured logically as row changes. In order to switch to `logical` WAL level, do the following, once:
```sql
ALTER SYSTEM SET wal_level = logical;
```
Then you need to restart the Postgres server, otherwise the change wouldn't take effect. After a restart, verify with:
```sql
SHOW wal_level;
 wal_level 
-----------
 logical
(1 row)
```

Then, you need to create a "logical replication slot".
You can do that by calling a builtin function and passing two parameters to it - the first is the name of your slot,
and you can pick whatever name you like. The second is the plugin used, and it needs to match the shared library name
you compiled above, so `pg_turso`.
```sql
SELECT pg_create_logical_replication_slot('pg_turso_slot', 'pg_turso');
```

Then, you can fill the table with some data:
```sql
INSERT INTO menu VALUES (1, 'salami', 2.49);
INSERT INTO menu VALUES (2, 'pastrami', 4.99);
INSERT INTO menu VALUES (3, 'wasabi', 1.99);
```

No replication has happened yet. In Postgres, replication is triggered by calling a function. This function takes the replication slot name and optional parameters.
pg_turso requires two parameters - the `url` and the `token`, to be able to communicate with a Turso instance, e.g.
```sql
SELECT * FROM pg_logical_slot_get_changes('pg_turso_slot', NULL, NULL, 'url', 'https://your-unique-link.turso.io/', 'auth', 's3cr3t-p4s5');
```
Note that this is a regular `SELECT` statement, so you're free to fetch the secret token value from another table, if it should remain secret.

The call triggers parsing WAL and processing all the logical changes. These changes are sent to Turso.

## How to use the pg_turso extension with helper functions

Instead of replicating manually, you can use our `pg_turso` extension. It's based on [pg_cron](https://github.com/citusdata/pg_cron) and allows the replication to be automated.

1. Set up Turso authentication - helper functions that return the database URL and token
```sql
-- token
CREATE OR REPLACE FUNCTION turso_token() RETURNS text LANGUAGE SQL AS $$ SELECT <your-token-generated-with-turso-db-tokens-create>; $$;

-- url
CREATE OR REPLACE FUNCTION turso_url() RETURNS text LANGUAGE SQL AS $$ SELECT 'https://workerscounter-psarna.turso.io/'; $$;
```

2. Load the extension and schedule replication. The interval accepts `pg_cron` syntax.

```sql
CREATE EXTENSION pg_turso;
SELECT turso_schedule_mv_replication('assorted_collection_of_dirt_cheap_dishes', '30 seconds'); -- refreshing materialized views in Postgres is costly, beware!
```

Voilà! Your data is now replicated to Turso.

## Replicating tables

On top of replicating parts of your table to Turso as Postgres materialized views, you can also use `pg_turso` to replicate tables. In the future, we're also considering adding custom filters to table replication. In order to replicate a table, simply call:
```sql
CREATE EXTENSION pg_turso;
SELECT turso_schedule_table_replication('assorted_collection_of_dirt_cheap_dishes', '5 seconds');
```
Table replication is also more efficient than materialized view replication, because it does not involve refreshing the materialized view. Enjoy!

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