Doc: fix db_engines section and improve config reference #674
1 changed files with 29 additions and 26 deletions
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@ -107,44 +107,47 @@ on how to operate Garage in such a setup.
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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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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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| [LMDB](https://www.lmdb.tech) (default since `v0.9.0`) | `"lmdb"` | `<metadata_dir>/db.lmdb/` |
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| [Sled](https://sled.rs) (default up to `v0.8.0`) | `"sled"` | `<metadata_dir>/db/` |
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| [Sqlite](https://sqlite.org) | `"sqlite"` | `<metadata_dir>/db.sqlite` |
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Sled was the only database engine up to Garage v0.7.0. Performance issues and
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API limitations of Sled prompted the addition of alternative engines in v0.8.0.
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Since v0.9.0, LMDB is the default engine instead of Sled, and Sled is
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deprecated. We plan to remove Sled in Garage v1.0.
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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 traditional 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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- Sled: tends to produce large data files and also has performance issues,
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especially when the metadata folder is on a traditional HDD and not on SSD.
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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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- LMDB: the recommended database engine on 64-bit systems, much more
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space-efficient and slightly faster. Note that the data format of LMDB is not
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portable between architectures, so for instance the Garage database of an
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x86-64 node cannot be moved to an ARM64 node. Also note that, while LMDB can
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technically be used on 32-bit systems, this will limit your node to very
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small database sizes due to how LMDB works; it is therefore not recommended.
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- Sqlite: Garage supports Sqlite as an alternative storage backend for
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metadata, and although it has not been tested as much, it is expected to work
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satisfactorily. Since Garage v0.9.0, performance issues have largely been
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fixed by allowing for a no-fsync mode (see `metadata_fsync`). Sqlite does not
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have the database size limitation of LMDB on 32-bit systems.
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It is possible to convert Garage's metadata directory from one format to another
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using the `garage convert-db` command, which should be used as follows:
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```
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convert-db -a <input db engine> -i <input db path> \
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garage 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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Make sure to specify the full database path as presented in the table above
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(third colummn), and not just the path to the metadata directory.
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### `metadata_fsync`
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