Add mirroring section documentation

docs/configuration/index.md

@@ -25,6 +25,8 @@ Since PgDog uses TOML, both `5000` and `5_000` are valid numbers. Configuration
 |------|-------------|
 | [General](pgdog.toml/general.md) | General pooler settings like `host`, `port` and various timeouts. |
 | [Databases](pgdog.toml/databases.md) | PostgreSQL databases proxied by PgDog. |
+| [Mirroring](pgdog.toml/mirroring.md) | Configuration to [mirror](../features/mirroring.md) databases for testing |
+| [Sharded Tables](pgdog.toml/sharded_tables.md) | Configuration for [sharding](../features/sharding/basics.md) databases |
 | [Plugins](pgdog.toml/plugins.md) | Plugins configuration. |
 | [Users](users.toml/users.md) | List of users (with passwords) that are allowed to connect to PgDog. |
 | [Admin](pgdog.toml/admin.md) | Admin database settings like admin password. |

docs/configuration/pgdog.toml/databases.md

@@ -72,14 +72,6 @@ The shard number for this database. Only required if your database contains more
 
 Default: **`0`**
 
-### `mirror_of`
-
-Indicates this database is a mirror of another one. All traffic sent to the `mirror_of` database will also be replayed against this database, subject to [`mirror_exposure`](general.md#mirror_exposure) setting.
-
-For clusters with multiple databases, `mirror_of` must be identical in all entries. Otherwise, mirroring will be automatically disabled for that database.
-
-Default: **`none`**
-
 !!! note
     All settings below take priority over values in [`[general]`](general.md) and [`[[users]]`](../users.toml/users.md) config sections.
 

docs/configuration/pgdog.toml/mirroring.md

@@ -0,0 +1,37 @@
+# Mirroring
+
+Mirroring settings configure a mirroring setup between two databases. This causes traffic to be copied to the destination database for testing purposes: More details on [mirroring](../../features/mirroring.md)
+
+```toml
+[[mirroring]]
+source_db = "source"
+destination_db = "dest"
+queue_depth = 500 # optional, overrides global setting
+exposure = 0.1 # optional, overrides global setting
+```
+
+### `source_db`
+
+Name of the source database. This should be a `name` set up in
+[the `databases` section of the configuration.](./databases.md)
+
+Default: **none** (required)
+
+### `destination_db`
+
+Name of the destination database. This should be a `name` set up
+in [the `databases` section of the configuration.](./databases.md)
+
+Default: **none** (required)
+
+### `queue_depth`
+
+The length of the queue to provision. See [mirroring](../../features/mirroring.md) for more details. This overrides the [general](./general.md) setting `mirror_queue`
+
+Default: **none** (optional)
+
+### `exposure`
+
+The percent of transactions to mirror, as a floating point number between 0.0 and 1.0 . See [mirroring](../../features/mirroring.md) for more details. This overrides the [general](./general.md) setting `mirror_exposure`
+
+Default: **none** (optional)

docs/features/mirroring.md

@@ -17,7 +17,7 @@ Mirroring in PgDog is asynchronous and should have minimal impact production dat
 
 ### Configure mirroring
 
-To use mirroring, first configure both the mirror and the production database in [`pgdog.toml`](../configuration/pgdog.toml/general.md). Once both databases are running, add `mirror_of` to all instances of the mirror database:
+To use mirroring, first configure both the mirror and the production database in [`pgdog.toml`](../configuration/pgdog.toml/general.md). Once both databases are running, add a `[[mirroring]]` section:
 
 ```toml
 [[databases]]
@@ -27,7 +27,12 @@ host = "10.0.0.1"
 [[databases]]
 name = "staging_db"
 host = "10.0.2.25"
-mirror_of = "prod"
+
+[[mirroring]]
+source_db = "prod"
+destination_db = "staging_db"
+# queue_length = 256  # Optional: overrides general.mirror_queue
+# exposure = 0.5      # Optional: overrides general.mirror_exposure
 ```
 
 !!! note
@@ -48,6 +53,17 @@ If the mirror database(s) can't keep up with production traffic, queries will ba
 mirror_queue = 500
 ```
 
+Or in the individual `[[mirroring]]` section:
+
+```toml
+[[mirroring]]
+source_db = 'source'
+destination_db = 'dest'
+queue_depth = 500
+```
+
+Note that local `[[mirroring]]` configuration overrides the `general` settings for that mirror only.
+
 If the queue gets full, all subsequent mirrored transactions will be dropped until there is space in the queue again.
 
 !!! note
@@ -64,6 +80,17 @@ This is configurable using a percentage, relative to the amount of transactions
 mirror_exposure = 0.5 # 50%
 ```
 
+Or in the specific mirroring section:
+
+```toml
+[[mirroring]]
+source_db = 'source'
+destination_db = 'dest'
+exposure = 0.5
+```
+
+Local config in `[[mirroring]]` overwrites the `[general]` value for that mirror.
+
 Acceptable values are between **0.0** (0%) and **1.0** (100%).
 
 This is changeable at runtime, without restarting PgDog. When adding a mirror, it's a good idea to start slow, e.g., with only 0.1% exposure (`mirror_exposure = 0.01`), and gradually increase it over time.