ClickHouse/docs/en/operations/system-tables/stack_trace.md

# system.stack_trace {#system-tables_stack_trace}

Contains stack traces of all server threads. Allows developers to introspect the server state.

To analyze stack frames, use the `addressToLine`, `addressToLineWithInlines`, `addressToSymbol` and `demangle` [introspection functions](../../sql-reference/functions/introspection.md).

Columns:

-   `thread_name` ([String](../../sql-reference/data-types/string.md)) — Thread name.
-   `thread_id` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Thread identifier.
-   `query_id` ([String](../../sql-reference/data-types/string.md)) — Query identifier that can be used to get details about a query that was running from the [query_log](../system-tables/query_log.md) system table.
-   `trace` ([Array(UInt64)](../../sql-reference/data-types/array.md)) — A [stack trace](https://en.wikipedia.org/wiki/Stack_trace) which represents a list of physical addresses where the called methods are stored.

**Example**

Enabling introspection functions:

``` sql
SET allow_introspection_functions = 1;
```

Getting symbols from ClickHouse object files:

``` sql
WITH arrayMap(x -> demangle(addressToSymbol(x)), trace) AS all SELECT thread_name, thread_id, query_id, arrayStringConcat(all, '\n') AS res FROM system.stack_trace LIMIT 1 \G;
```

``` text
Row 1:
──────
thread_name: clickhouse-serv

thread_id: 686
query_id:  1a11f70b-626d-47c1-b948-f9c7b206395d
res:       sigqueue
DB::StorageSystemStackTrace::fillData(std::__1::vector<COW<DB::IColumn>::mutable_ptr<DB::IColumn>, std::__1::allocator<COW<DB::IColumn>::mutable_ptr<DB::IColumn> > >&, DB::Context const&, DB::SelectQueryInfo const&) const
DB::IStorageSystemOneBlock<DB::StorageSystemStackTrace>::read(std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&, DB::SelectQueryInfo const&, DB::Context const&, DB::QueryProcessingStage::Enum, unsigned long, unsigned int)
DB::InterpreterSelectQuery::executeFetchColumns(DB::QueryProcessingStage::Enum, DB::QueryPipeline&, std::__1::shared_ptr<DB::PrewhereInfo> const&, std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&)
DB::InterpreterSelectQuery::executeImpl(DB::QueryPipeline&, std::__1::shared_ptr<DB::IBlockInputStream> const&, std::__1::optional<DB::Pipe>)
DB::InterpreterSelectQuery::execute()
DB::InterpreterSelectWithUnionQuery::execute()
DB::executeQueryImpl(char const*, char const*, DB::Context&, bool, DB::QueryProcessingStage::Enum, bool, DB::ReadBuffer*)
DB::executeQuery(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, DB::Context&, bool, DB::QueryProcessingStage::Enum, bool)
DB::TCPHandler::runImpl()
DB::TCPHandler::run()
Poco::Net::TCPServerConnection::start()
Poco::Net::TCPServerDispatcher::run()
Poco::PooledThread::run()
Poco::ThreadImpl::runnableEntry(void*)
start_thread
__clone
```

Getting filenames and line numbers in ClickHouse source code:

``` sql
WITH arrayMap(x -> addressToLine(x), trace) AS all, arrayFilter(x -> x LIKE '%/dbms/%', all) AS dbms SELECT thread_name, thread_id, query_id, arrayStringConcat(notEmpty(dbms) ? dbms : all, '\n') AS res FROM system.stack_trace LIMIT 1 \G;
```

``` text
Row 1:
──────
thread_name: clickhouse-serv

thread_id: 686
query_id:  cad353e7-1c29-4b2e-949f-93e597ab7a54
res:       /lib/x86_64-linux-gnu/libc-2.27.so
/build/obj-x86_64-linux-gnu/../src/Storages/System/StorageSystemStackTrace.cpp:182
/build/obj-x86_64-linux-gnu/../contrib/libcxx/include/vector:656
/build/obj-x86_64-linux-gnu/../src/Interpreters/InterpreterSelectQuery.cpp:1338
/build/obj-x86_64-linux-gnu/../src/Interpreters/InterpreterSelectQuery.cpp:751
/build/obj-x86_64-linux-gnu/../contrib/libcxx/include/optional:224
/build/obj-x86_64-linux-gnu/../src/Interpreters/InterpreterSelectWithUnionQuery.cpp:192
/build/obj-x86_64-linux-gnu/../src/Interpreters/executeQuery.cpp:384
/build/obj-x86_64-linux-gnu/../src/Interpreters/executeQuery.cpp:643
/build/obj-x86_64-linux-gnu/../src/Server/TCPHandler.cpp:251
/build/obj-x86_64-linux-gnu/../src/Server/TCPHandler.cpp:1197
/build/obj-x86_64-linux-gnu/../contrib/poco/Net/src/TCPServerConnection.cpp:57
/build/obj-x86_64-linux-gnu/../contrib/libcxx/include/atomic:856
/build/obj-x86_64-linux-gnu/../contrib/poco/Foundation/include/Poco/Mutex_POSIX.h:59
/build/obj-x86_64-linux-gnu/../contrib/poco/Foundation/include/Poco/AutoPtr.h:223
/lib/x86_64-linux-gnu/libpthread-2.27.so
/lib/x86_64-linux-gnu/libc-2.27.so
```

**See Also**

-   [Introspection Functions](../../sql-reference/functions/introspection.md) — Which introspection functions are available and how to use them.
-   [system.trace_log](../system-tables/trace_log.md) — Contains stack traces collected by the sampling query profiler.
-   [arrayMap](../../sql-reference/functions/array-functions.md#array-map) — Description and usage example of the `arrayMap` function.
-   [arrayFilter](../../sql-reference/functions/array-functions.md#array-filter) — Description and usage example of the `arrayFilter` function.