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Add docs for predefined_http (#8161)
* Add docs for predefined_http * fix review suggestions Co-authored-by: Ivan Blinkov <github@blinkov.ru>
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@ -278,4 +278,227 @@ You can create a query with parameters and pass values for them from the corresp
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$ curl -sS "<address>?param_id=2¶m_phrase=test" -d "SELECT * FROM table WHERE int_column = {id:UInt8} and string_column = {phrase:String}"
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$ curl -sS "<address>?param_id=2¶m_phrase=test" -d "SELECT * FROM table WHERE int_column = {id:UInt8} and string_column = {phrase:String}"
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```
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```
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[Original article](https://clickhouse.tech/docs/en/interfaces/http_interface/) <!--hide-->
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## Predefined HTTP Interface {#predefined_http_interface}
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ClickHouse supports specific queries through the HTTP interface. For example, you can write data to a table as follows:
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```bash
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$ echo '(4),(5),(6)' | curl 'http://localhost:8123/?query=INSERT%20INTO%20t%20VALUES' --data-binary @-
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```
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ClickHouse also supports Predefined HTTP Interface which can help you more easy integration with third party tools like [Prometheus exporter](https://github.com/percona-lab/clickhouse_exporter).
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Example:
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* First of all, add this section to server configuration file:
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``` xml
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<http_handlers>
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<predefine_query_handler>
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<url>/metrics</url>
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<method>GET</method>
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<queries>
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<query>SELECT * FROM system.metrics LIMIT 5 FORMAT Template SETTINGS format_template_resultset = 'prometheus_template_output_format_resultset', format_template_row = 'prometheus_template_output_format_row', format_template_rows_between_delimiter = '\n'</query>
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</queries>
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</predefine_query_handler>
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</http_handlers>
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```
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* You can now request the url directly for data in the Prometheus format:
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``` bash
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curl -vvv 'http://localhost:8123/metrics'
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* Trying ::1...
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* Connected to localhost (::1) port 8123 (#0)
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> GET /metrics HTTP/1.1
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> Host: localhost:8123
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> User-Agent: curl/7.47.0
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> Accept: */*
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>
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< HTTP/1.1 200 OK
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< Date: Wed, 27 Nov 2019 08:54:25 GMT
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< Connection: Keep-Alive
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< Content-Type: text/plain; charset=UTF-8
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< X-ClickHouse-Server-Display-Name: i-tl62qd0o
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< Transfer-Encoding: chunked
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< X-ClickHouse-Query-Id: f39235f6-6ed7-488c-ae07-c7ceafb960f6
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< Keep-Alive: timeout=3
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< X-ClickHouse-Summary: {"read_rows":"0","read_bytes":"0","written_rows":"0","written_bytes":"0","total_rows_to_read":"0"}
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<
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# HELP "Query" "Number of executing queries"
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# TYPE "Query" counter
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"Query" 1
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# HELP "Merge" "Number of executing background merges"
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# TYPE "Merge" counter
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"Merge" 0
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# HELP "PartMutation" "Number of mutations (ALTER DELETE/UPDATE)"
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# TYPE "PartMutation" counter
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"PartMutation" 0
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# HELP "ReplicatedFetch" "Number of data parts being fetched from replica"
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# TYPE "ReplicatedFetch" counter
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"ReplicatedFetch" 0
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# HELP "ReplicatedSend" "Number of data parts being sent to replicas"
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# TYPE "ReplicatedSend" counter
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"ReplicatedSend" 0
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* Connection #0 to host localhost left intact
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```
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As you can see from the example, if `<http_handlers>` is configured in the config.xml file, ClickHouse will match the HTTP requests received to the predefined type in `<http_handlers>`, then ClickHouse will execute the corresponding predefined query if the match is successful.
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Now `<http_handlers>` can configure `<root_handler>`, `<ping_handler>`, `<replicas_status_handler>`, `<dynamic_query_handler>` and `<no_handler_description>` .
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## root_handler
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`<root_handler>` returns the specified content for the root path request. The specific return content is configured by `http_server_default_response` in config.xml. if not specified, return **Ok.**
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`http_server_default_response` is not defined and an HTTP request is sent to ClickHouse. The result is as follows:
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```xml
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<http_handlers>
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<root_handler/>
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</http_handlers>
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```
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```
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$ curl 'http://localhost:8123'
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Ok.
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```
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`http_server_default_response` is defined and an HTTP request is sent to ClickHouse. The result is as follows:
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```xml
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<http_server_default_response><![CDATA[<html ng-app="SMI2"><head><base href="http://ui.tabix.io/"></head><body><div ui-view="" class="content-ui"></div><script src="http://loader.tabix.io/master.js"></script></body></html>]]></http_server_default_response>
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<http_handlers>
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<root_handler/>
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</http_handlers>
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```
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```
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$ curl 'http://localhost:8123'
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<html ng-app="SMI2"><head><base href="http://ui.tabix.io/"></head><body><div ui-view="" class="content-ui"></div><script src="http://loader.tabix.io/master.js"></script></body></html>%
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```
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## ping_handler
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`<ping_handler>` can be used to probe the health of the current ClickHouse Server. When the ClickHouse HTTP Server is normal, accessing ClickHouse through `<ping_handler>` will return **Ok.**.
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Example:
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```xml
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<http_handlers>
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<ping_handler>/ping</ping_handler>
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</http_handlers>
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```
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```bash
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$ curl 'http://localhost:8123/ping'
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Ok.
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```
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## replicas_status_handler
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`<replicas_status_handler>` is used to detect the state of the replica node and return **Ok.** if the replica node has no delay. If there is a delay, return the specific delay. The value of `<replicas_status_handler>` supports customization. If you do not specify `<replicas_status_handler>`, ClickHouse default setting `<replicas_status_handler>` is **/replicas_status**.
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Example:
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```xml
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<http_handlers>
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<replicas_status_handler>/replicas_status</replicas_status_handler>
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</http_handlers>
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```
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No delay case:
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```bash
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$ curl 'http://localhost:8123/replicas_status'
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Ok.
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```
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Delayed case:
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```bash
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$ curl 'http://localhost:8123/replicas_status'
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db.stats: Absolute delay: 22. Relative delay: 22.
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```
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## predefined_query_handler
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You can configure `<method>`, `<headers>`, `<url>` and `<queries>` in `<predefined_query_handler>`.
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`<method>` is responsible for matching the method part of the HTTP request. `<method>` fully conforms to the definition of [method](https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods) in the HTTP protocol. It is an optional configuration. If it is not defined in the configuration file, it does not match the method portion of the HTTP request
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`<url>` is responsible for matching the url part of the HTTP request. It is compatible with [RE2](https://github.com/google/re2)'s regular expressions. It is an optional configuration. If it is not defined in the configuration file, it does not match the url portion of the HTTP request
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`<headers>` is responsible for matching the header part of the HTTP request. It is compatible with RE2's regular expressions. It is an optional configuration. If it is not defined in the configuration file, it does not match the header portion of the HTTP request
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`<queries>` value is a predefined query of `<predefined_query_handler>`, which is executed by ClickHouse when an HTTP request is matched and the result of the query is returned. It is a must configuration.
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`<predefined_query_handler>` supports setting Settings and query_params values.
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The following example defines the values of `max_threads` and `max_alter_threads` settings, then queries the system table to check whether these settings were set successfully.
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Example:
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```xml
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<root_handlers>
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<predefined_query_handler>
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<method>GET</method>
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<headers>
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<XXX>TEST_HEADER_VALUE</XXX>
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<PARAMS_XXX><![CDATA[(?P<name_1>[^/]+)(/(?P<name_2>[^/]+))?]]></PARAMS_XXX>
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</headers>
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<url><![CDATA[/query_param_with_url/\w+/(?P<name_1>[^/]+)(/(?P<name_2>[^/]+))?]]></url>
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<queries>
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<query>SELECT value FROM system.settings WHERE name = {name_1:String}</query>
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<query>SELECT name, value FROM system.settings WHERE name = {name_2:String}</query>
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</queries>
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</predefined_query_handler>
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</root_handlers>
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```
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```bash
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$ curl -H 'XXX:TEST_HEADER_VALUE' -H 'PARAMS_XXX:max_threads' 'http://localhost:8123/query_param_with_url/1/max_threads/max_alter_threads?max_threads=1&max_alter_threads=2'
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1
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max_alter_threads 2
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```
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!!! note "Note"
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In one `<predefined_query_handler>`, one `<queries>` only supports one `<query>` of an insert type.
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## dynamic_query_handler
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`<dynamic_query_handler>` than `<predefined_query_handler>` increased `<query_param_name>` .
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ClickHouse extracts and executes the value corresponding to the `<query_param_name>` value in the url of the HTTP request.
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ClickHouse default setting `<query_param_name>` is `/query` . It is an optional configuration. If there is no definition in the configuration file, the param is not passed in.
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To experiment with this functionality, the example defines the values of max_threads and max_alter_threads and queries whether the Settings were set successfully.
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The difference is that in `<predefined_query_handler>`, query is wrote in the configuration file. But in `<dynamic_query_handler>`, query is written in the form of param of the HTTP request.
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Example:
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```xml
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<root_handlers>
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<dynamic_query_handler>
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<headers>
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<XXX>TEST_HEADER_VALUE_DYNAMIC</XXX>
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<PARAMS_XXX><![CDATA[(?P<param_name_1>[^/]+)(/(?P<param_name_2>[^/]+))?]]></PARAMS_XXX>
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</headers>
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<query_param_name>query_param</query_param_name>
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</dynamic_query_handler>
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</root_handlers>
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```
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```bash
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$ curl -H 'XXX:TEST_HEADER_VALUE_DYNAMIC' -H 'PARAMS_XXX:max_threads' 'http://localhost:8123/?query_param=SELECT%20value%20FROM%20system.settings%20where%20name%20=%20%7Bname_1:String%7D%20OR%20name%20=%20%7Bname_2:String%7D&max_threads=1&max_alter_threads=2¶m_name_2=max_alter_threads'
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1
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2
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```
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[Original article](https://clickhouse.tech/docs/en/interfaces/http_interface/) <!--hide-->
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