Query Distributed Table Return UNEXPECTED_PACKET_FROM_SERVER

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Introduction

ClickHouse is a column-store database management system that provides high-performance analytics and data processing capabilities. However, users may encounter errors when querying distributed tables, such as the UNEXPECTED_PACKET_FROM_SERVER error. In this article, we will investigate the cause of this error and provide a solution.

Error Message

The error message is as follows:

Received exception from server (version 25.5.1):
Code: 102. DB::Exception: Received from localhost:9000. DB::Exception: Unexpected packet from server a8test-211:9000 (expected TablesStatusResponse, got Data): While executing Delayed. (UNEXPECTED_PACKET_FROM_SERVER)

Observations

The error occurs only when max_parallel_replicas is not set, i.e., when using the default value 1000 in version 25.5.1.2782. When running the same query with max_parallel_replicas = 1, it works fine and does not trigger the error.

System Configuration

The system configuration is as follows:

  • ClickHouse version: 25.5.1.2782
  • Cluster name: cluster_2S_2R
  • max_parallel_replicas setting: not set (default value 1000)

Query

The query that triggers the error is as follows:

SELECT
    remote_addr
FROM
    ops_hxlb_all
WHERE
    http_host = 'blog.hhg.com'
ORDER BY
    http_host DESC
LIMIT 5

Stacktrace

The stacktrace is as follows:

0. DB::Exception::Exception(DB::Exception::MessageMasked&&, int, bool) @ 0x000000000fccc51b
1. DB::Connection::throwUnexpectedPacket(DB::TimeoutSetter&, unsigned long, char const*) @ 0x00000000152cd849
2. DB::Connection::getTablesStatus(DB::ConnectionTimeouts const&, DB::TablesStatusRequest const&) @ 0x00000000152cf6a6
3. DB::ConnectionEstablisher::run(PoolWithFailoverBase<DB::IConnectionPool>::TryResult&, String&, bool) @ 0x00000000152e265c
4. DB::ConnectionPoolWithFailover::tryGetEntry(std::shared_ptr<DB::IConnectionPool> const&, DB::ConnectionTimeouts const&, String&, DB::Settings const&, DB::QualifiedTableName const*, std::function<void (int, Poco::Timespan, DB::AsyncEventTimeoutType, String const&, unsigned int)>) @ 0x00000000152f0e6e
5. PoolWithFailoverBase<DB::IConnectionPool>::TryResult std::__function::__policy_invoker<PoolWithFailoverBase<DB::IConnectionPool>::TryResult (std::shared_ptr<DB::IConnectionPool> const&, String&)>::__call_impl[abi:ne190107]<std::__function::__default_alloc_func<DB::ConnectionPoolWithFailover::getManyChecked(DB::ConnectionTimeouts const&, DB::Settings const&, DB::PoolMode, DB::QualifiedTableName const&, std::function<void (int, Poco::Timespan, DB::AsyncEventTimeoutType, String const&, unsigned int)>, std::optional<bool>, std::function<Priority (unsigned long)>)::$_0, PoolWithFailoverBase<DB::IConnectionPool>::TryResult (std::shared_ptr<DB::IConnectionPool> const&, String&)>>(std::__function::__policy_storage const*, std::shared_ptr<DB::IConnectionPool> const&, String&) (.llvm.2136841370659154313) @ 0x00000000152f1c8e
6. PoolWithFailoverBase<DB::IConnectionPool>::getMany(unsigned long, unsigned long, unsigned long, unsigned long, bool, bool, std::function<PoolWithFailoverBase<DB::IConnectionPool>::TryResult (std::shared_ptr<DB::IConnectionPool> const&, String&)> const&, std::function<Priority (unsigned long)> const&) @ 0x00000000152ef5d9
7. DB::ConnectionPoolWithFailover::getManyImpl(DB::Settings const&, DB::PoolMode, std::function<PoolWithFailoverBase<DB::IConnectionPool>::TryResult (std::shared_ptr<DB::IConnectionPool> const&, String&)> const&, std::optional<bool>, std::function<Priority (unsigned long)>, bool) @ 0x00000000152eeeb0
8. DB::ConnectionPoolWithFailover::getManyChecked(DB::ConnectionTimeouts const&, DB::Settings const&, DB::PoolMode, DB::QualifiedTableName const&, std::function<void (int, Poco::Timespan, DB::AsyncEventTimeoutType, String const&, unsigned int)>, std::optional<bool>, std::function<Priority (unsigned long)>) @ 0x00000000152ef17b
9. DB::QueryPipelineBuilder std::__function::__policy_invoker<DB::QueryPipelineBuilder ()>::__call_impl[abi:ne190107]<std::__function::__default_alloc_func<DB::ReadFromRemote::addLazyPipe(std::vector<DB::Pipe, std::allocator<DB::Pipe>>&, DB::ClusterProxy::SelectStreamFactory::Shard const&, DB::Block const&)::$_0, DB::QueryPipelineBuilder ()>>(std::__function::__policy_storage const*) @ 0x0000000015a55b77
10. DB::DelayedSource::work() @ 0x0000000015849549
11. DB::ExecutionThreadContext::executeTask() @ 0x00000000154cb6c9
12. DB::PipelineExecutor::executeStepImpl(unsigned long, std::atomic<bool>*) @ 0x00000000154bf178
13. void std::__function::__policy_invoker<void ()>::__call_impl[abi:ne190107]<std::__function::__default_alloc_func<DB::PipelineExecutor::spawnThreadsImpl(std::shared_ptr<DB::IAcquiredSlot>)::$_0, void ()>>(std::__function::__policy_storage const*) @ 0x00000000154c199f
14. ThreadPoolImpl<ThreadFromGlobalPoolImpl<false, true>>::ThreadFromThreadPool::worker() @ 0x000000000fe1146b
15. void std::__function::__policy_invoker<void ()>::__call_impl[abi:ne190107]<std::__function::__default_alloc_func<ThreadFromGlobalPoolImpl<false, true>::ThreadFromGlobalPoolImpl<void (Impl<ThreadFromGlobalPoolImpl<false, true>>::ThreadFromThreadPool::*)(), ThreadPoolImpl<ThreadFromGlobalPoolImpl<false, true>>::ThreadFromThreadPool*>(void (ThreadPoolImpl<ThreadFromGlobalPoolImpl<false, true>>::ThreadFromThreadPool::*&&)(), ThreadPoolImpl<ThreadFromGlobalPoolImpl<false, true>>::ThreadFromThreadPool*&&)::'lambda'(), void ()>>(std::__function::__policy_storage const*) @ 0x000000000fe18083
16. ThreadPoolImpl<std::thread>::ThreadFromThreadPool::worker() @ 0x000000000fe0e692
17. void* std::__thread_proxy[abi:ne190107]<std::tuple<std::unique_ptr<std::__thread_struct, std::default_delete<std::__thread_struct>>, void (ThreadPoolImpl<std::thread>::ThreadFromThreadPool::*)(), ThreadPoolImpl<std::thread>::ThreadFromThreadPool*>>(void*) @ 0x000000000fe15b5a
18. start_thread @ 0x00000000000081ca
19. __GI___clone @ 0x00000000000398d3

Cause of the Error

The cause of the error is due to the fact that the max_parallel_replicas setting is not set, which causes the system to use the default value of 1000. This setting controls the number of parallel replicas that can be used for a query. When this setting is not set, the system may try to use more replicas than available, leading to the UNEXPECTED_PACKET_FROM_SERVER error.

Solution

To solve this issue, you can set the max_parallel_replicas setting to a value that is less than or equal to the number of available replicas. For example, you can set it to 1, which will allow the system to use only one replica for the query.

You can set the max_parallel_replicas setting using the following SQL command:

SET max_parallel_replicas = 1;

Alternatively, you can set the max_parallel_replicas setting in the ClickHouse configuration file (clickhouse-server.conf) by adding the following line:

max_parallel_replicas = 1

Conclusion

Q: What is the UNEXPECTED_PACKET_FROM_SERVER error in ClickHouse?

A: The UNEXPECTED_PACKET_FROM_SERVER error is a type of error that occurs in ClickHouse when the system receives an unexpected packet from a server. This error can occur due to various reasons, including network issues, configuration problems, or bugs in the ClickHouse code.

Q: What causes the UNEXPECTED_PACKET_FROM_SERVER error in ClickHouse?

A: The UNEXPECTED_PACKET_FROM_SERVER error in ClickHouse can be caused by various factors, including:

  • Network issues: Problems with the network connection between the client and the server can cause the UNEXPECTED_PACKET_FROM_SERVER error.
  • Configuration problems: Incorrect configuration settings, such as setting the max_parallel_replicas setting to a value that is too high, can cause the UNEXPECTED_PACKET_FROM_SERVER error.
  • Bugs in the ClickHouse code: Bugs in the ClickHouse code can cause the UNEXPECTED_PACKET_FROM_SERVER error.

Q: How can I troubleshoot the UNEXPECTED_PACKET_FROM_SERVER error in ClickHouse?

A: To troubleshoot the UNEXPECTED_PACKET_FROM_SERVER error in ClickHouse, you can try the following steps:

  • Check the network connection: Make sure that the network connection between the client and the server is stable and working correctly.
  • Check the configuration settings: Verify that the configuration settings, such as the max_parallel_replicas setting, are correct and not causing the error.
  • Check the ClickHouse logs: Check the ClickHouse logs for any error messages that may indicate the cause of the UNEXPECTED_PACKET_FROM_SERVER error.
  • Contact ClickHouse support: If none of the above steps resolve the issue, contact ClickHouse support for further assistance.

Q: How can I prevent the UNEXPECTED_PACKET_FROM_SERVER error in ClickHouse?

A: To prevent the UNEXPECTED_PACKET_FROM_SERVER error in ClickHouse, you can try the following steps:

  • Set the max_parallel_replicas setting to a value that is less than or equal to the number of available replicas.
  • Verify that the network connection between the client and the server is stable and working correctly.
  • Regularly check and update the ClickHouse code to ensure that it is up-to-date and free of bugs.
  • Use ClickHouse's built-in features, such as the query_log setting, to monitor and troubleshoot queries.

Q: What are some common mistakes that can cause the UNEXPECTED_PACKET_FROM_SERVER error in ClickHouse?

A: Some common mistakes that can cause the UNEXPECTED_PACKET_FROM_SERVER error in ClickHouse include:

  • Setting the max_parallel_replicas setting to a value that is too high.
  • Not verifying the network connection between the client and the server.
  • Not regularly checking and updating the ClickHouse code.
  • Not using ClickHouse's built-in features to monitor and troubleshoot queries.

Q: How can I contact ClickHouse support for further assistance?

A: To contact ClickHouse support for further assistance, you can:

  • Visit the ClickHouse website and submit a support request.
  • Email the ClickHouse support team directly.
  • Join the ClickHouse community forum and ask for help from other users.
  • Contact your ClickHouse sales representative for assistance.