--- toc_priority: 65 toc_title: Introspection --- # Introspection Functions {#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 "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 {#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) ``` **Parameters** - `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 ``` ## addressToSymbol {#addresstosymbol} Converts virtual memory address inside ClickHouse server process to the symbol from ClickHouse object files. **Syntax** ``` sql addressToSymbol(address_of_binary_instruction) ``` **Parameters** - `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 {#demangle} Converts a symbol that you can get using the [addressToSymbol](#addresstosymbol) function to the C++ function name. **Syntax** ``` sql demangle(symbol) ``` **Parameters** - `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 {#tid} Returns id of the thread, in which current [Block](https://clickhouse.tech/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 {#logtrace} Emits trace log message to server log for each [Block](https://clickhouse.tech/docs/en/development/architecture/#block). **Syntax** ``` sql logTrace('message') ``` **Parameters** - `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 │ └──────────────────────────────┘ ``` [Original article](https://clickhouse.tech/docs/en/query_language/functions/introspection/)