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How does the ClickHouse distributed query run on every shard?

asked 2021-09-20 11:00:00 +0000

bukephalos gravatar image

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answered 2023-02-08 16:00:00 +0000

lakamha gravatar image

The ClickHouse distributed query runs on every shard in the following steps:

  1. The client sends a distributed query to the ClickHouse server.
  2. The query is parsed and optimized at the server level.
  3. The server identifies the list of shards that the query needs to be executed on.
  4. The query is then sent to each shard for execution.
  5. The shards execute the query in parallel on their respective data sets.
  6. The intermediate results are collected by the server and combined together.
  7. Final results are returned to the client.

During the execution of the distributed query, the server coordinates with each shard to ensure that the query is executed consistently and correctly across all shards. This coordination is done using the ClickHouse distributed engine, which is responsible for managing the distributed query execution. The engine handles node discovery, data distribution, and fault-tolerance during the query execution.

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Asked: 2021-09-20 11:00:00 +0000

Seen: 1 times

Last updated: Feb 08 '23