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---
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slug: /en/sql-reference/functions/introspection
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sidebar_position: 100
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sidebar_label: Introspection
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---
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# Introspection Functions
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You can use functions described in this chapter to introspect [ELF ](https://en.wikipedia.org/wiki/Executable_and_Linkable_Format ) and [DWARF ](https://en.wikipedia.org/wiki/DWARF ) for query profiling.
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:::note
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These functions are slow and may impose security considerations.
:::
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For proper operation of introspection functions:
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- Install the `clickhouse-common-static-dbg` package.
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- Set the [allow_introspection_functions ](../../operations/settings/settings.md#allow_introspection_functions ) setting to 1.
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For security reasons introspection functions are disabled by default.
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ClickHouse saves profiler reports to the [trace_log ](../../operations/system-tables/trace_log.md#system_tables-trace_log ) system table. Make sure the table and profiler are configured properly.
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## addressToLine
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Converts virtual memory address inside ClickHouse server process to the filename and the line number in ClickHouse source code.
If you use official ClickHouse packages, you need to install the `clickhouse-common-static-dbg` package.
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**Syntax**
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``` sql
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addressToLine(address_of_binary_instruction)
```
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**Arguments**
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- `address_of_binary_instruction` ([UInt64](../data-types/int-uint.md)) — Address of instruction in a running process.
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**Returned value**
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- Source code filename and the line number in this file delimited by colon.
For example, `/build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.cpp:199` , where `199` is a line number.
- Name of a binary, if the function couldn’ t find the debug information.
- Empty string, if the address is not valid.
Type: [String ](../../sql-reference/data-types/string.md ).
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**Example**
Enabling introspection functions:
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``` sql
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SET allow_introspection_functions=1;
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```
Selecting the first string from the `trace_log` system table:
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``` sql
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SELECT * FROM system.trace_log LIMIT 1 \G;
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```
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``` text
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Row 1:
──────
event_date: 2019-11-19
event_time: 2019-11-19 18:57:23
revision: 54429
timer_type: Real
thread_number: 48
query_id: 421b6855-1858-45a5-8f37-f383409d6d72
trace: [140658411141617,94784174532828,94784076370703,94784076372094,94784076361020,94784175007680,140658411116251,140658403895439]
```
The `trace` field contains the stack trace at the moment of sampling.
Getting the source code filename and the line number for a single address:
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``` sql
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SELECT addressToLine(94784076370703) \G;
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```
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``` text
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Row 1:
──────
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addressToLine(94784076370703): /build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.cpp:199
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```
Applying the function to the whole stack trace:
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``` sql
SELECT
arrayStringConcat(arrayMap(x -> addressToLine(x), trace), '\n') AS trace_source_code_lines
FROM system.trace_log
LIMIT 1
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\G
```
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The [arrayMap ](../../sql-reference/functions/array-functions.md#array-map ) function allows to process each individual element of the `trace` array by the `addressToLine` function. The result of this processing you see in the `trace_source_code_lines` column of output.
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``` text
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Row 1:
──────
trace_source_code_lines: /lib/x86_64-linux-gnu/libpthread-2.27.so
/usr/lib/debug/usr/bin/clickhouse
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/build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.cpp:199
/build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.h:155
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/usr/include/c++/9/bits/atomic_base.h:551
/usr/lib/debug/usr/bin/clickhouse
/lib/x86_64-linux-gnu/libpthread-2.27.so
/build/glibc-OTsEL5/glibc-2.27/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:97
```
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## addressToLineWithInlines
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Similar to `addressToLine` , but returns an Array with all inline functions. As a result of this, it is slower than `addressToLine` .
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:::note
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If you use official ClickHouse packages, you need to install the `clickhouse-common-static-dbg` package.
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:::
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**Syntax**
``` sql
addressToLineWithInlines(address_of_binary_instruction)
```
**Arguments**
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- `address_of_binary_instruction` ([UInt64](../data-types/int-uint.md)) — Address of instruction in a running process.
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**Returned value**
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- An array whose first element is the source code filename and line number in the file delimited by a colon. From the second element onwards, inline functions' source code filenames, line numbers and function names are listed. If the function couldn’ t find the debug information, then an array with a single element equal to the name of the binary is returned, otherwise an empty array is returned if the address is not valid. [Array(String) ](../data-types/array.md ).
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**Example**
Enabling introspection functions:
``` sql
SET allow_introspection_functions=1;
```
Applying the function to address.
```sql
SELECT addressToLineWithInlines(531055181::UInt64);
```
``` text
┌─addressToLineWithInlines(CAST('531055181', 'UInt64'))────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ ['./src/Functions/addressToLineWithInlines.cpp:98','./build_normal_debug/./src/Functions/addressToLineWithInlines.cpp:176:DB::(anonymous namespace)::FunctionAddressToLineWithInlines::implCached(unsigned long) const'] │
└──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
```
Applying the function to the whole stack trace:
``` sql
SELECT
ta, addressToLineWithInlines(arrayJoin(trace) as ta)
FROM system.trace_log
WHERE
query_id = '5e173544-2020-45de-b645-5deebe2aae54';
```
The [arrayJoin ](../../sql-reference/functions/array-functions.md#array-functions-join ) functions will split array to rows.
``` text
┌────────ta─┬─addressToLineWithInlines(arrayJoin(trace))───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ 365497529 │ ['./build_normal_debug/./contrib/libcxx/include/string_view:252'] │
│ 365593602 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:191'] │
│ 365593866 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:0'] │
│ 365592528 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:0'] │
│ 365591003 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:477'] │
│ 365590479 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:442'] │
│ 365590600 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:457'] │
│ 365598941 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:0'] │
│ 365607098 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:0'] │
│ 365590571 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:451'] │
│ 365598941 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:0'] │
│ 365607098 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:0'] │
│ 365590571 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:451'] │
│ 365598941 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:0'] │
│ 365607098 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:0'] │
│ 365590571 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:451'] │
│ 365598941 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:0'] │
│ 365597289 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:807'] │
│ 365599840 │ ['./build_normal_debug/./src/Common/Dwarf.cpp:1118'] │
│ 531058145 │ ['./build_normal_debug/./src/Functions/addressToLineWithInlines.cpp:152'] │
│ 531055181 │ ['./src/Functions/addressToLineWithInlines.cpp:98','./build_normal_debug/./src/Functions/addressToLineWithInlines.cpp:176:DB::(anonymous namespace)::FunctionAddressToLineWithInlines::implCached(unsigned long) const'] │
│ 422333613 │ ['./build_normal_debug/./src/Functions/IFunctionAdaptors.h:21'] │
│ 586866022 │ ['./build_normal_debug/./src/Functions/IFunction.cpp:216'] │
│ 586869053 │ ['./build_normal_debug/./src/Functions/IFunction.cpp:264'] │
│ 586873237 │ ['./build_normal_debug/./src/Functions/IFunction.cpp:334'] │
│ 597901620 │ ['./build_normal_debug/./src/Interpreters/ExpressionActions.cpp:601'] │
│ 597898534 │ ['./build_normal_debug/./src/Interpreters/ExpressionActions.cpp:718'] │
│ 630442912 │ ['./build_normal_debug/./src/Processors/Transforms/ExpressionTransform.cpp:23'] │
│ 546354050 │ ['./build_normal_debug/./src/Processors/ISimpleTransform.h:38'] │
│ 626026993 │ ['./build_normal_debug/./src/Processors/ISimpleTransform.cpp:89'] │
│ 626294022 │ ['./build_normal_debug/./src/Processors/Executors/ExecutionThreadContext.cpp:45'] │
│ 626293730 │ ['./build_normal_debug/./src/Processors/Executors/ExecutionThreadContext.cpp:63'] │
│ 626169525 │ ['./build_normal_debug/./src/Processors/Executors/PipelineExecutor.cpp:213'] │
│ 626170308 │ ['./build_normal_debug/./src/Processors/Executors/PipelineExecutor.cpp:178'] │
│ 626166348 │ ['./build_normal_debug/./src/Processors/Executors/PipelineExecutor.cpp:329'] │
│ 626163461 │ ['./build_normal_debug/./src/Processors/Executors/PipelineExecutor.cpp:84'] │
│ 626323536 │ ['./build_normal_debug/./src/Processors/Executors/PullingAsyncPipelineExecutor.cpp:85'] │
│ 626323277 │ ['./build_normal_debug/./src/Processors/Executors/PullingAsyncPipelineExecutor.cpp:112'] │
│ 626323133 │ ['./build_normal_debug/./contrib/libcxx/include/type_traits:3682'] │
│ 626323041 │ ['./build_normal_debug/./contrib/libcxx/include/tuple:1415'] │
└───────────┴──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
```
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## addressToSymbol
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Converts virtual memory address inside ClickHouse server process to the symbol from ClickHouse object files.
**Syntax**
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``` sql
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addressToSymbol(address_of_binary_instruction)
```
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**Arguments**
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- `address_of_binary_instruction` ([UInt64](../data-types/int-uint.md)) — Address of instruction in a running process.
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**Returned value**
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- Symbol from ClickHouse object files. [String ](../data-types/string.md ).
- Empty string, if the address is not valid. [String ](../data-types/string.md ).
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**Example**
Enabling introspection functions:
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``` sql
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SET allow_introspection_functions=1;
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```
Selecting the first string from the `trace_log` system table:
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``` sql
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SELECT * FROM system.trace_log LIMIT 1 \G;
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```
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``` text
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Row 1:
──────
event_date: 2019-11-20
event_time: 2019-11-20 16:57:59
revision: 54429
timer_type: Real
thread_number: 48
query_id: 724028bf-f550-45aa-910d-2af6212b94ac
trace: [94138803686098,94138815010911,94138815096522,94138815101224,94138815102091,94138814222988,94138806823642,94138814457211,94138806823642,94138814457211,94138806823642,94138806795179,94138806796144,94138753770094,94138753771646,94138753760572,94138852407232,140399185266395,140399178045583]
```
The `trace` field contains the stack trace at the moment of sampling.
Getting a symbol for a single address:
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``` sql
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SELECT addressToSymbol(94138803686098) \G;
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```
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``` text
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Row 1:
──────
addressToSymbol(94138803686098): _ZNK2DB24IAggregateFunctionHelperINS_20AggregateFunctionSumImmNS_24AggregateFunctionSumDataImEEEEE19addBatchSinglePlaceEmPcPPKNS_7IColumnEPNS_5ArenaE
```
Applying the function to the whole stack trace:
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``` sql
SELECT
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arrayStringConcat(arrayMap(x -> addressToSymbol(x), trace), '\n') AS trace_symbols
FROM system.trace_log
LIMIT 1
\G
```
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The [arrayMap ](../../sql-reference/functions/array-functions.md#array-map ) function allows to process each individual element of the `trace` array by the `addressToSymbols` function. The result of this processing you see in the `trace_symbols` column of output.
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``` text
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Row 1:
──────
trace_symbols: _ZNK2DB24IAggregateFunctionHelperINS_20AggregateFunctionSumImmNS_24AggregateFunctionSumDataImEEEEE19addBatchSinglePlaceEmPcPPKNS_7IColumnEPNS_5ArenaE
_ZNK2DB10Aggregator21executeWithoutKeyImplERPcmPNS0_28AggregateFunctionInstructionEPNS_5ArenaE
_ZN2DB10Aggregator14executeOnBlockESt6vectorIN3COWINS_7IColumnEE13immutable_ptrIS3_EESaIS6_EEmRNS_22AggregatedDataVariantsERS1_IPKS3_SaISC_EERS1_ISE_SaISE_EERb
_ZN2DB10Aggregator14executeOnBlockERKNS_5BlockERNS_22AggregatedDataVariantsERSt6vectorIPKNS_7IColumnESaIS9_EERS6_ISB_SaISB_EERb
_ZN2DB10Aggregator7executeERKSt10shared_ptrINS_17IBlockInputStreamEERNS_22AggregatedDataVariantsE
_ZN2DB27AggregatingBlockInputStream8readImplEv
_ZN2DB17IBlockInputStream4readEv
_ZN2DB26ExpressionBlockInputStream8readImplEv
_ZN2DB17IBlockInputStream4readEv
_ZN2DB26ExpressionBlockInputStream8readImplEv
_ZN2DB17IBlockInputStream4readEv
_ZN2DB28AsynchronousBlockInputStream9calculateEv
_ZNSt17_Function_handlerIFvvEZN2DB28AsynchronousBlockInputStream4nextEvEUlvE_E9_M_invokeERKSt9_Any_data
_ZN14ThreadPoolImplI20ThreadFromGlobalPoolE6workerESt14_List_iteratorIS0_E
_ZZN20ThreadFromGlobalPoolC4IZN14ThreadPoolImplIS_E12scheduleImplIvEET_St8functionIFvvEEiSt8optionalImEEUlvE1_JEEEOS4_DpOT0_ENKUlvE_clEv
_ZN14ThreadPoolImplISt6threadE6workerESt14_List_iteratorIS0_E
execute_native_thread_routine
start_thread
clone
```
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## demangle
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Converts a symbol that you can get using the [addressToSymbol ](#addresstosymbol ) function to the C++ function name.
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**Syntax**
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``` sql
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demangle(symbol)
```
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**Arguments**
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- `symbol` ([String](../data-types/string.md)) — Symbol from an object file.
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**Returned value**
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- Name of the C++ function, or an empty string if the symbol is not valid. [String ](../data-types/string.md ).
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**Example**
Enabling introspection functions:
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``` sql
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SET allow_introspection_functions=1;
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```
Selecting the first string from the `trace_log` system table:
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``` sql
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SELECT * FROM system.trace_log LIMIT 1 \G;
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```
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``` text
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Row 1:
──────
event_date: 2019-11-20
event_time: 2019-11-20 16:57:59
revision: 54429
timer_type: Real
thread_number: 48
query_id: 724028bf-f550-45aa-910d-2af6212b94ac
trace: [94138803686098,94138815010911,94138815096522,94138815101224,94138815102091,94138814222988,94138806823642,94138814457211,94138806823642,94138814457211,94138806823642,94138806795179,94138806796144,94138753770094,94138753771646,94138753760572,94138852407232,140399185266395,140399178045583]
```
The `trace` field contains the stack trace at the moment of sampling.
Getting a function name for a single address:
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``` sql
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SELECT demangle(addressToSymbol(94138803686098)) \G;
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```
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``` text
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Row 1:
──────
demangle(addressToSymbol(94138803686098)): DB::IAggregateFunctionHelper< DB::AggregateFunctionSum < unsigned long , unsigned long , DB::AggregateFunctionSumData < unsigned long > > >::addBatchSinglePlace(unsigned long, char*, DB::IColumn const**, DB::Arena*) const
```
Applying the function to the whole stack trace:
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``` sql
SELECT
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arrayStringConcat(arrayMap(x -> demangle(addressToSymbol(x)), trace), '\n') AS trace_functions
FROM system.trace_log
LIMIT 1
\G
```
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The [arrayMap ](../../sql-reference/functions/array-functions.md#array-map ) function allows to process each individual element of the `trace` array by the `demangle` function. The result of this processing you see in the `trace_functions` column of output.
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``` text
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Row 1:
──────
trace_functions: DB::IAggregateFunctionHelper< DB::AggregateFunctionSum < unsigned long , unsigned long , DB::AggregateFunctionSumData < unsigned long > > >::addBatchSinglePlace(unsigned long, char*, DB::IColumn const**, DB::Arena*) const
DB::Aggregator::executeWithoutKeyImpl(char*& , unsigned long, DB::Aggregator::AggregateFunctionInstruction*, DB::Arena*) const
DB::Aggregator::executeOnBlock(std::vector< COW < DB::IColumn > ::immutable_ptr< DB::IColumn > , std::allocator< COW < DB::IColumn > ::immutable_ptr< DB::IColumn > > >, unsigned long, DB::AggregatedDataVariants& , std::vector< DB::IColumn const * , std::allocator < DB::IColumn const * > >& , std::vector< std::vector < DB::IColumn const * , std::allocator < DB::IColumn const * > >, std::allocator< std::vector < DB::IColumn const * , std::allocator < DB::IColumn const * > > > >& , bool& )
DB::Aggregator::executeOnBlock(DB::Block const& , DB::AggregatedDataVariants& , std::vector< DB::IColumn const * , std::allocator < DB::IColumn const * > >& , std::vector< std::vector < DB::IColumn const * , std::allocator < DB::IColumn const * > >, std::allocator< std::vector < DB::IColumn const * , std::allocator < DB::IColumn const * > > > >& , bool& )
DB::Aggregator::execute(std::shared_ptr< DB::IBlockInputStream > const& , DB::AggregatedDataVariants& )
DB::AggregatingBlockInputStream::readImpl()
DB::IBlockInputStream::read()
DB::ExpressionBlockInputStream::readImpl()
DB::IBlockInputStream::read()
DB::ExpressionBlockInputStream::readImpl()
DB::IBlockInputStream::read()
DB::AsynchronousBlockInputStream::calculate()
std::_Function_handler< void ( ) , DB::AsynchronousBlockInputStream::next ( ) :: { lambda ( ) # 1 } > ::_M_invoke(std::_Any_data const& )
ThreadPoolImpl< ThreadFromGlobalPool > ::worker(std::_List_iterator< ThreadFromGlobalPool > )
ThreadFromGlobalPool::ThreadFromGlobalPool< ThreadPoolImpl < ThreadFromGlobalPool > ::scheduleImpl< void > (std::function< void ( ) > , int, std::optional< unsigned long > )::{lambda()#3}>(ThreadPoolImpl< ThreadFromGlobalPool > ::scheduleImpl< void > (std::function< void ( ) > , int, std::optional< unsigned long > )::{lambda()#3}& & )::{lambda()#1}::operator()() const
ThreadPoolImpl< std::thread > ::worker(std::_List_iterator< std::thread > )
execute_native_thread_routine
start_thread
clone
```
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## tid
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Returns id of the thread, in which current [Block ](https://clickhouse.com/docs/en/development/architecture/#block ) is processed.
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**Syntax**
``` sql
tid()
```
**Returned value**
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- Current thread id. [Uint64 ](../data-types/int-uint.md#uint-ranges ).
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**Example**
Query:
``` sql
SELECT tid();
```
Result:
``` text
┌─tid()─┐
│ 3878 │
└───────┘
```
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## logTrace
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Emits trace log message to server log for each [Block ](https://clickhouse.com/docs/en/development/architecture/#block ).
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**Syntax**
``` sql
logTrace('message')
```
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**Arguments**
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- `message` — Message that is emitted to server log. [String ](../data-types/string.md#string ).
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**Returned value**
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- Always returns 0.
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**Example**
Query:
``` sql
SELECT logTrace('logTrace message');
```
Result:
``` text
┌─logTrace('logTrace message')─┐
│ 0 │
└──────────────────────────────┘
```