--- 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. :::warning 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 > >::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 > >::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::immutable_ptr, std::allocator::immutable_ptr > >, unsigned long, DB::AggregatedDataVariants&, std::vector >&, std::vector >, std::allocator > > >&, bool&) DB::Aggregator::executeOnBlock(DB::Block const&, DB::AggregatedDataVariants&, std::vector >&, std::vector >, std::allocator > > >&, bool&) DB::Aggregator::execute(std::shared_ptr 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::_M_invoke(std::_Any_data const&) ThreadPoolImpl::worker(std::_List_iterator) ThreadFromGlobalPool::ThreadFromGlobalPool::scheduleImpl(std::function, int, std::optional)::{lambda()#3}>(ThreadPoolImpl::scheduleImpl(std::function, int, std::optional)::{lambda()#3}&&)::{lambda()#1}::operator()() const ThreadPoolImpl::worker(std::_List_iterator) 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 │ └──────────────────────────────┘ ```