Arbitrary Query Parameter?

[jcdang]

We are load balancing queries on clickhouse with affinity based on a query string parameter. It would be useful if there was some arbitrary parameter we could use to route the queries. We're using temp tables and a group of queries need to go to the same box.

[blinkov]

Why can't you just keep separate jdbc connections to all instances and choose the appropriate one depending on that query parameter?

[jcdang]

We can, although it's more of an architectural design reason to keep this kind of logic out of the application. You don't generally don't want to manage load balancing as a concern at an app level.

[meshpaul]

Sounds like you need a single instance of CH DB for temp work. Or it should be replicated.

[jcdang]

Correct. It's a bit of both since the primary tables are replicated. The temp tables are used for short term filtering and processing.

[zhicwu]

Starting from 0.3.2, both request headers and query parameters can be customized. Of course this is limited to http protocol.

• Java Client - use CUSTOM_HEADERS and CUSTOM_PARAMS options:

  request.option(ClickHouseHttpOption.CUSTOM_HEADERS, "Header 1=value1,Header 2=value2")
    .option(ClickHouseHttpOption.CUSTOM_PARAMS, "parameter1=value1,parameter2=value2")

• JDBC - use custom_http_headers and custom_http_params two properties.