27 lines
2.6 KiB
Markdown
27 lines
2.6 KiB
Markdown
# ClickHouse
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`clickhouse://host:port?username=user&password=password&database=clicks&x-multi-statement=true`
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| URL Query | Description |
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|------------|-------------|
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| `x-migrations-table`| Name of the migrations table |
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| `x-migrations-table-engine`| Engine to use for the migrations table, defaults to TinyLog |
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| `x-cluster-name` | Name of cluster for creating `schema_migrations` table cluster wide |
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| `database` | The name of the database to connect to |
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| `username` | The user to sign in as |
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| `password` | The user's password |
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| `host` | The host to connect to. |
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| `port` | The port to bind to. |
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| `x-multi-statement` | false | Enable multiple statements to be ran in a single migration (See note below) |
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## Notes
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* The Clickhouse driver does not natively support executing multiple statements in a single query. To allow for multiple statements in a single migration, you can use the `x-multi-statement` param. There are two important caveats:
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* This mode splits the migration text into separately-executed statements by a semi-colon `;`. Thus `x-multi-statement` cannot be used when a statement in the migration contains a string with a semi-colon.
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* The queries are not executed in any sort of transaction/batch, meaning you are responsible for fixing partial migrations.
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* Using the default TinyLog table engine for the schema_versions table prevents backing up the table if using the [clickhouse-backup](https://github.com/AlexAkulov/clickhouse-backup) tool. If backing up the database with make sure the migrations are run with `x-migrations-table-engine=MergeTree`.
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* Clickhouse cluster mode is not officially supported, since it's not tested right now, but you can try enabling `schema_migrations` table replication by specifying a `x-cluster-name`:
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* When `x-cluster-name` is specified, `x-migrations-table-engine` also should be specified. See the docs regarding [replicated table engines](https://clickhouse.tech/docs/en/engines/table-engines/mergetree-family/replication/#table_engines-replication).
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* When `x-cluster-name` is specified, only the `schema_migrations` table is replicated across the cluster. You still need to write your migrations so that the application tables are replicated within the cluster.
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* If you want to create database inside the migration, you should know, that table which will manage migrations `schema-migrations table` will be in `default` table, so you can't use `USE <database_name>` inside migration. In this case you may not specify the database in the connection string (example you can find [here](examples/migrations/003_create_database.up.sql))
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