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Document db_engine
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@ -9,6 +9,8 @@ Here is an example `garage.toml` configuration file that illustrates all of the
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metadata_dir = "/var/lib/garage/meta"
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metadata_dir = "/var/lib/garage/meta"
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data_dir = "/var/lib/garage/data"
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data_dir = "/var/lib/garage/data"
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db_engine = "lmdb"
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block_size = 1048576
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block_size = 1048576
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replication_mode = "3"
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replication_mode = "3"
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@ -71,6 +73,47 @@ This folder can be placed on an HDD. The space available for `data_dir`
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should be counted to determine a node's capacity
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should be counted to determine a node's capacity
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when [adding it to the cluster layout](@/documentation/cookbook/real-world.md).
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when [adding it to the cluster layout](@/documentation/cookbook/real-world.md).
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### `db_engine` (since `v0.8.0`)
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By default, Garage uses the Sled embedded database library
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to store its metadata on-disk. Since `v0.8.0`, Garage can use alternative storage backends as follows:
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| DB engine | `db_engine` value | Database path |
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| --------- | ----------------- | ------------- |
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| [Sled](https://sled.rs) | `"sled"` | `<metadata_dir>/db/` |
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| [LMDB](https://www.lmdb.tech) | `"lmdb"` | `<metadata_dir>/db.lmdb/` |
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| [Sqlite](https://sqlite.org) | `"sqlite"` | `<metadata_dir>/db.sqlite` |
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Performance characteristics of the different DB engines are as follows:
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- Sled: the default database engine, which tends to produce
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large data files and also has performance issues, especially when the metadata folder
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is on a traditionnal HDD and not on SSD.
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- LMDB: the recommended alternative on 64-bit systems,
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much more space-efficiant and slightly faster. Note that the data format of LMDB is not portable
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between architectures, so for instance the Garage database of an x86-64
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node cannot be moved to an ARM64 node. Also note that, while LMDB can technically be used on 32-bit systems,
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this will limit your node to very small database sizes due to how LMDB works; it is therefore not recommended.
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- Sqlite: Garage supports Sqlite as a storage backend for metadata,
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however it may have issues and is also very slow in its current implementation,
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so it is not recommended to be used for now.
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It is possible to convert Garage's metadata directory from one format to another with a small utility named `convert_db`,
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which can be downloaded at the following locations:
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[for amd64](https://garagehq.deuxfleurs.fr/_releases/convert_db/amd64/convert_db),
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[for i386](https://garagehq.deuxfleurs.fr/_releases/convert_db/i386/convert_db),
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[for arm64](https://garagehq.deuxfleurs.fr/_releases/convert_db/arm64/convert_db),
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[for arm](https://garagehq.deuxfleurs.fr/_releases/convert_db/arm/convert_db).
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The `convert_db` utility is used as folows:
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```
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convert-db -a <input db engine> -i <input db path> \
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-b <output db engine> -o <output db path>
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```
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Make sure to specify the full database path as presented in the table above,
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and not just the path to the metadata directory.
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### `block_size`
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### `block_size`
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Garage splits stored objects in consecutive chunks of size `block_size`
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Garage splits stored objects in consecutive chunks of size `block_size`
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