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168 lines
9.1 KiB
Markdown
168 lines
9.1 KiB
Markdown
---
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toc_priority: 10
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toc_title: RabbitMQ
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---
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# RabbitMQ Engine {#rabbitmq-engine}
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This engine allows integrating ClickHouse with [RabbitMQ](https://www.rabbitmq.com).
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`RabbitMQ` lets you:
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- Publish or subscribe to data flows.
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- Process streams as they become available.
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## Creating a Table {#table_engine-rabbitmq-creating-a-table}
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``` sql
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CREATE TABLE [IF NOT EXISTS] [db.]table_name [ON CLUSTER cluster]
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(
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name1 [type1] [DEFAULT|MATERIALIZED|ALIAS expr1],
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name2 [type2] [DEFAULT|MATERIALIZED|ALIAS expr2],
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...
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) ENGINE = RabbitMQ SETTINGS
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rabbitmq_host_port = 'host:port',
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rabbitmq_exchange_name = 'exchange_name',
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rabbitmq_format = 'data_format'[,]
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[rabbitmq_exchange_type = 'exchange_type',]
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[rabbitmq_routing_key_list = 'key1,key2,...',]
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[rabbitmq_row_delimiter = 'delimiter_symbol',]
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[rabbitmq_schema = '',]
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[rabbitmq_num_consumers = N,]
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[rabbitmq_num_queues = N,]
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[rabbitmq_queue_base = 'queue',]
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[rabbitmq_deadletter_exchange = 'dl-exchange',]
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[rabbitmq_persistent = 0,]
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[rabbitmq_skip_broken_messages = N,]
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[rabbitmq_max_block_size = N,]
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[rabbitmq_flush_interval_ms = N]
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```
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Required parameters:
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- `rabbitmq_host_port` – host:port (for example, `localhost:5672`).
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- `rabbitmq_exchange_name` – RabbitMQ exchange name.
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- `rabbitmq_format` – Message format. Uses the same notation as the SQL `FORMAT` function, such as `JSONEachRow`. For more information, see the [Formats](../../../interfaces/formats.md) section.
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Optional parameters:
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- `rabbitmq_exchange_type` – The type of RabbitMQ exchange: `direct`, `fanout`, `topic`, `headers`, `consistent_hash`. Default: `fanout`.
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- `rabbitmq_routing_key_list` – A comma-separated list of routing keys.
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- `rabbitmq_row_delimiter` – Delimiter character, which ends the message.
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- `rabbitmq_schema` – Parameter that must be used if the format requires a schema definition. For example, [Cap’n Proto](https://capnproto.org/) requires the path to the schema file and the name of the root `schema.capnp:Message` object.
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- `rabbitmq_num_consumers` – The number of consumers per table. Default: `1`. Specify more consumers if the throughput of one consumer is insufficient.
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- `rabbitmq_num_queues` – Total number of queues. Default: `1`. Increasing this number can significantly improve performance.
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- `rabbitmq_queue_base` - Specify a hint for queue names. Use cases of this setting are described below.
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- `rabbitmq_deadletter_exchange` - Specify name for a [dead letter exchange](https://www.rabbitmq.com/dlx.html). You can create another table with this exchange name and collect messages in cases when they are republished to dead letter exchange. By default dead letter exchange is not specified.
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- `rabbitmq_persistent` - If set to 1 (true), in insert query delivery mode will be set to 2 (marks messages as 'persistent'). Default: `0`.
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- `rabbitmq_skip_broken_messages` – RabbitMQ message parser tolerance to schema-incompatible messages per block. Default: `0`. If `rabbitmq_skip_broken_messages = N` then the engine skips *N* RabbitMQ messages that cannot be parsed (a message equals a row of data).
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- `rabbitmq_max_block_size`
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- `rabbitmq_flush_interval_ms`
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Also format settings can be added along with rabbitmq-related settings.
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Example:
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``` sql
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CREATE TABLE queue (
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key UInt64,
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value UInt64,
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date DateTime
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) ENGINE = RabbitMQ SETTINGS rabbitmq_host_port = 'localhost:5672',
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rabbitmq_exchange_name = 'exchange1',
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rabbitmq_format = 'JSONEachRow',
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rabbitmq_num_consumers = 5,
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date_time_input_format = 'best_effort';
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```
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The RabbitMQ server configuration should be added using the ClickHouse config file.
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Required configuration:
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``` xml
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<rabbitmq>
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<username>root</username>
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<password>clickhouse</password>
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</rabbitmq>
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```
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Additional configuration:
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``` xml
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<rabbitmq>
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<vhost>clickhouse</vhost>
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</rabbitmq>
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```
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## Description {#description}
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`SELECT` is not particularly useful for reading messages (except for debugging), because each message can be read only once. It is more practical to create real-time threads using [materialized views](../../../sql-reference/statements/create/view.md). To do this:
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1. Use the engine to create a RabbitMQ consumer and consider it a data stream.
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2. Create a table with the desired structure.
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3. Create a materialized view that converts data from the engine and puts it into a previously created table.
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When the `MATERIALIZED VIEW` joins the engine, it starts collecting data in the background. This allows you to continually receive messages from RabbitMQ and convert them to the required format using `SELECT`.
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One RabbitMQ table can have as many materialized views as you like.
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Data can be channeled based on `rabbitmq_exchange_type` and the specified `rabbitmq_routing_key_list`.
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There can be no more than one exchange per table. One exchange can be shared between multiple tables - it enables routing into multiple tables at the same time.
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Exchange type options:
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- `direct` - Routing is based on the exact matching of keys. Example table key list: `key1,key2,key3,key4,key5`, message key can equal any of them.
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- `fanout` - Routing to all tables (where exchange name is the same) regardless of the keys.
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- `topic` - Routing is based on patterns with dot-separated keys. Examples: `*.logs`, `records.*.*.2020`, `*.2018,*.2019,*.2020`.
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- `headers` - Routing is based on `key=value` matches with a setting `x-match=all` or `x-match=any`. Example table key list: `x-match=all,format=logs,type=report,year=2020`.
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- `consistent_hash` - Data is evenly distributed between all bound tables (where the exchange name is the same). Note that this exchange type must be enabled with RabbitMQ plugin: `rabbitmq-plugins enable rabbitmq_consistent_hash_exchange`.
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Setting `rabbitmq_queue_base` may be used for the following cases:
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- to let different tables share queues, so that multiple consumers could be registered for the same queues, which makes a better performance. If using `rabbitmq_num_consumers` and/or `rabbitmq_num_queues` settings, the exact match of queues is achieved in case these parameters are the same.
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- to be able to restore reading from certain durable queues when not all messages were successfully consumed. To resume consumption from one specific queue - set its name in `rabbitmq_queue_base` setting and do not specify `rabbitmq_num_consumers` and `rabbitmq_num_queues` (defaults to 1). To resume consumption from all queues, which were declared for a specific table - just specify the same settings: `rabbitmq_queue_base`, `rabbitmq_num_consumers`, `rabbitmq_num_queues`. By default, queue names will be unique to tables.
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- to reuse queues as they are declared durable and not auto-deleted. (Can be deleted via any of RabbitMQ CLI tools.)
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To improve performance, received messages are grouped into blocks the size of [max_insert_block_size](../../../operations/server-configuration-parameters/settings.md#settings-max_insert_block_size). If the block wasn’t formed within [stream_flush_interval_ms](../../../operations/server-configuration-parameters/settings.md) milliseconds, the data will be flushed to the table regardless of the completeness of the block.
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If `rabbitmq_num_consumers` and/or `rabbitmq_num_queues` settings are specified along with `rabbitmq_exchange_type`, then:
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- `rabbitmq-consistent-hash-exchange` plugin must be enabled.
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- `message_id` property of the published messages must be specified (unique for each message/batch).
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For insert query there is message metadata, which is added for each published message: `messageID` and `republished` flag (true, if published more than once) - can be accessed via message headers.
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Do not use the same table for inserts and materialized views.
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Example:
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``` sql
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CREATE TABLE queue (
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key UInt64,
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value UInt64
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) ENGINE = RabbitMQ SETTINGS rabbitmq_host_port = 'localhost:5672',
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rabbitmq_exchange_name = 'exchange1',
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rabbitmq_exchange_type = 'headers',
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rabbitmq_routing_key_list = 'format=logs,type=report,year=2020',
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rabbitmq_format = 'JSONEachRow',
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rabbitmq_num_consumers = 5;
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CREATE TABLE daily (key UInt64, value UInt64)
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ENGINE = MergeTree() ORDER BY key;
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CREATE MATERIALIZED VIEW consumer TO daily
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AS SELECT key, value FROM queue;
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SELECT key, value FROM daily ORDER BY key;
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```
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## Virtual Columns {#virtual-columns}
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- `_exchange_name` - RabbitMQ exchange name.
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- `_channel_id` - ChannelID, on which consumer, who received the message, was declared.
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- `_delivery_tag` - DeliveryTag of the received message. Scoped per channel.
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- `_redelivered` - `redelivered` flag of the message.
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- `_message_id` - messageID of the received message; non-empty if was set, when message was published.
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- `_timestamp` - timestamp of the received message; non-empty if was set, when message was published.
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[Original article](https://clickhouse.tech/docs/en/engines/table-engines/integrations/rabbitmq/) <!--hide-->
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