ClickHouse/docs/en/sql-reference/functions/introspection.md

---
slug: /en/sql-reference/functions/introspection
sidebar_position: 65
sidebar_label: Introspection
---

# Introspection Functions

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.

:::note    
These functions are slow and may impose security considerations.
:::

For proper operation of introspection functions:

-   Install the `clickhouse-common-static-dbg` package.

-   Set the [allow_introspection_functions](../../operations/settings/settings.md#settings-allow_introspection_functions) setting to 1.

        For security reasons introspection functions are disabled by default.

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.

## addressToLine

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.

**Syntax**

``` sql
addressToLine(address_of_binary_instruction)
```

**Arguments**

-   `address_of_binary_instruction` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Address of instruction in a running process.

**Returned value**

-   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).

**Example**

Enabling introspection functions:

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

Selecting the first string from the `trace_log` system table:

``` sql
SELECT * FROM system.trace_log LIMIT 1 \G;
```

``` text
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:

``` sql
SELECT addressToLine(94784076370703) \G;
```

``` text
Row 1:
──────
addressToLine(94784076370703): /build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.cpp:199
```

Applying the function to the whole stack trace:

``` sql
SELECT
    arrayStringConcat(arrayMap(x -> addressToLine(x), trace), '\n') AS trace_source_code_lines
FROM system.trace_log
LIMIT 1
\G
```

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.

``` text
Row 1:
──────
trace_source_code_lines: /lib/x86_64-linux-gnu/libpthread-2.27.so
/usr/lib/debug/usr/bin/clickhouse
/build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.cpp:199
/build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.h:155
/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
```

## addressToLineWithInlines

Similar to `addressToLine`, but it will return an Array with all inline functions, and will be much slower as a price.

If you use official ClickHouse packages, you need to install the `clickhouse-common-static-dbg` package.

**Syntax**

``` sql
addressToLineWithInlines(address_of_binary_instruction)
```

**Arguments**

-   `address_of_binary_instruction` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Address of instruction in a running process.

**Returned value**

-   Array which first element is source code filename and the line number in this file delimited by colon. And from second element, inline functions' source code filename and line number and function name are listed.

-   Array with single element which is name of a binary, if the function couldn’t find the debug information.

-   Empty array, if the address is not valid.

Type: [Array(String)](../../sql-reference/data-types/array.md).

**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']                                                                                                                                                             │
└───────────┴──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

```


## addressToSymbol

Converts virtual memory address inside ClickHouse server process to the symbol from ClickHouse object files.

**Syntax**

``` sql
addressToSymbol(address_of_binary_instruction)
```

**Arguments**

-   `address_of_binary_instruction` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Address of instruction in a running process.

**Returned value**

-   Symbol from ClickHouse object files.
-   Empty string, if the address is not valid.

Type: [String](../../sql-reference/data-types/string.md).

**Example**

Enabling introspection functions:

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

Selecting the first string from the `trace_log` system table:

``` sql
SELECT * FROM system.trace_log LIMIT 1 \G;
```

``` text
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:

``` sql
SELECT addressToSymbol(94138803686098) \G;
```

``` text
Row 1:
──────
addressToSymbol(94138803686098): _ZNK2DB24IAggregateFunctionHelperINS_20AggregateFunctionSumImmNS_24AggregateFunctionSumDataImEEEEE19addBatchSinglePlaceEmPcPPKNS_7IColumnEPNS_5ArenaE
```

Applying the function to the whole stack trace:

``` sql
SELECT
    arrayStringConcat(arrayMap(x -> addressToSymbol(x), trace), '\n') AS trace_symbols
FROM system.trace_log
LIMIT 1
\G
```

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.

``` text
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
```

## demangle

Converts a symbol that you can get using the [addressToSymbol](#addresstosymbol) function to the C++ function name.

**Syntax**

``` sql
demangle(symbol)
```

**Arguments**

-   `symbol` ([String](../../sql-reference/data-types/string.md)) — Symbol from an object file.

**Returned value**

-   Name of the C++ function.
-   Empty string if a symbol is not valid.

Type: [String](../../sql-reference/data-types/string.md).

**Example**

Enabling introspection functions:

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

Selecting the first string from the `trace_log` system table:

``` sql
SELECT * FROM system.trace_log LIMIT 1 \G;
```

``` text
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:

``` sql
SELECT demangle(addressToSymbol(94138803686098)) \G;
```

``` text
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:

``` sql
SELECT
    arrayStringConcat(arrayMap(x -> demangle(addressToSymbol(x)), trace), '\n') AS trace_functions
FROM system.trace_log
LIMIT 1
\G
```

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.

``` text
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
```
## tid

Returns id of the thread, in which current [Block](https://clickhouse.com/docs/en/development/architecture/#block) is processed.

**Syntax**

``` sql
tid()
```

**Returned value**

-   Current thread id. [Uint64](../../sql-reference/data-types/int-uint.md#uint-ranges).

**Example**

Query:

``` sql
SELECT tid();
```

Result:

``` text
┌─tid()─┐
│  3878 │
└───────┘
```

## logTrace

Emits trace log message to server log for each [Block](https://clickhouse.com/docs/en/development/architecture/#block).

**Syntax**

``` sql
logTrace('message')
```

**Arguments**

-   `message` — Message that is emitted to server log. [String](../../sql-reference/data-types/string.md#string).

**Returned value**

-   Always returns 0.

**Example**

Query:

``` sql
SELECT logTrace('logTrace message');
```

Result:

``` text
┌─logTrace('logTrace message')─┐
│                            0 │
└──────────────────────────────┘
```