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373 lines
12 KiB
Markdown
373 lines
12 KiB
Markdown
---
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toc_priority: 65
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toc_title: Introspection
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---
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# Introspection Functions {#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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!!! warning "Warning"
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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#settings-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 {#addresstoline}
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Converts virtual memory address inside ClickHouse server process to the filename and the line number in ClickHouse source code.
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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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```
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**Arguments**
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- `address_of_binary_instruction` ([UInt64](../../sql-reference/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.
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For example, `/build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.cpp:199`, where `199` is a line number.
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- Name of a binary, if the function couldn’t find the debug information.
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- Empty string, if the address is not valid.
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Type: [String](../../sql-reference/data-types/string.md).
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**Example**
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Enabling introspection functions:
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``` sql
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SET allow_introspection_functions=1
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```
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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:
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──────
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event_date: 2019-11-19
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event_time: 2019-11-19 18:57:23
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revision: 54429
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timer_type: Real
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thread_number: 48
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query_id: 421b6855-1858-45a5-8f37-f383409d6d72
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trace: [140658411141617,94784174532828,94784076370703,94784076372094,94784076361020,94784175007680,140658411116251,140658403895439]
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```
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The `trace` field contains the stack trace at the moment of sampling.
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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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──────
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addressToLine(94784076370703): /build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.cpp:199
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```
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Applying the function to the whole stack trace:
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``` sql
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SELECT
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arrayStringConcat(arrayMap(x -> addressToLine(x), trace), '\n') AS trace_source_code_lines
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FROM system.trace_log
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LIMIT 1
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\G
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```
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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:
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──────
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trace_source_code_lines: /lib/x86_64-linux-gnu/libpthread-2.27.so
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/usr/lib/debug/usr/bin/clickhouse
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/build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.cpp:199
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/build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.h:155
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/usr/include/c++/9/bits/atomic_base.h:551
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/usr/lib/debug/usr/bin/clickhouse
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/lib/x86_64-linux-gnu/libpthread-2.27.so
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/build/glibc-OTsEL5/glibc-2.27/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:97
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```
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## addressToSymbol {#addresstosymbol}
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Converts virtual memory address inside ClickHouse server process to the symbol from ClickHouse object files.
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**Syntax**
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``` sql
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addressToSymbol(address_of_binary_instruction)
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```
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**Arguments**
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- `address_of_binary_instruction` ([UInt64](../../sql-reference/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.
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- Empty string, if the address is not valid.
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Type: [String](../../sql-reference/data-types/string.md).
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**Example**
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Enabling introspection functions:
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``` sql
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SET allow_introspection_functions=1
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```
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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:
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──────
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event_date: 2019-11-20
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event_time: 2019-11-20 16:57:59
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revision: 54429
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timer_type: Real
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thread_number: 48
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query_id: 724028bf-f550-45aa-910d-2af6212b94ac
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trace: [94138803686098,94138815010911,94138815096522,94138815101224,94138815102091,94138814222988,94138806823642,94138814457211,94138806823642,94138814457211,94138806823642,94138806795179,94138806796144,94138753770094,94138753771646,94138753760572,94138852407232,140399185266395,140399178045583]
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```
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The `trace` field contains the stack trace at the moment of sampling.
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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:
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──────
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addressToSymbol(94138803686098): _ZNK2DB24IAggregateFunctionHelperINS_20AggregateFunctionSumImmNS_24AggregateFunctionSumDataImEEEEE19addBatchSinglePlaceEmPcPPKNS_7IColumnEPNS_5ArenaE
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```
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Applying the function to the whole stack trace:
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``` sql
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SELECT
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arrayStringConcat(arrayMap(x -> addressToSymbol(x), trace), '\n') AS trace_symbols
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FROM system.trace_log
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LIMIT 1
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\G
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```
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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:
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──────
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trace_symbols: _ZNK2DB24IAggregateFunctionHelperINS_20AggregateFunctionSumImmNS_24AggregateFunctionSumDataImEEEEE19addBatchSinglePlaceEmPcPPKNS_7IColumnEPNS_5ArenaE
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_ZNK2DB10Aggregator21executeWithoutKeyImplERPcmPNS0_28AggregateFunctionInstructionEPNS_5ArenaE
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_ZN2DB10Aggregator14executeOnBlockESt6vectorIN3COWINS_7IColumnEE13immutable_ptrIS3_EESaIS6_EEmRNS_22AggregatedDataVariantsERS1_IPKS3_SaISC_EERS1_ISE_SaISE_EERb
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_ZN2DB10Aggregator14executeOnBlockERKNS_5BlockERNS_22AggregatedDataVariantsERSt6vectorIPKNS_7IColumnESaIS9_EERS6_ISB_SaISB_EERb
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_ZN2DB10Aggregator7executeERKSt10shared_ptrINS_17IBlockInputStreamEERNS_22AggregatedDataVariantsE
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_ZN2DB27AggregatingBlockInputStream8readImplEv
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_ZN2DB17IBlockInputStream4readEv
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_ZN2DB26ExpressionBlockInputStream8readImplEv
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_ZN2DB17IBlockInputStream4readEv
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_ZN2DB26ExpressionBlockInputStream8readImplEv
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_ZN2DB17IBlockInputStream4readEv
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_ZN2DB28AsynchronousBlockInputStream9calculateEv
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_ZNSt17_Function_handlerIFvvEZN2DB28AsynchronousBlockInputStream4nextEvEUlvE_E9_M_invokeERKSt9_Any_data
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_ZN14ThreadPoolImplI20ThreadFromGlobalPoolE6workerESt14_List_iteratorIS0_E
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_ZZN20ThreadFromGlobalPoolC4IZN14ThreadPoolImplIS_E12scheduleImplIvEET_St8functionIFvvEEiSt8optionalImEEUlvE1_JEEEOS4_DpOT0_ENKUlvE_clEv
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_ZN14ThreadPoolImplISt6threadE6workerESt14_List_iteratorIS0_E
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execute_native_thread_routine
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start_thread
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clone
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```
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## demangle {#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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```
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**Arguments**
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- `symbol` ([String](../../sql-reference/data-types/string.md)) — Symbol from an object file.
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**Returned value**
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- Name of the C++ function.
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- Empty string if a symbol is not valid.
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Type: [String](../../sql-reference/data-types/string.md).
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**Example**
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Enabling introspection functions:
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``` sql
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SET allow_introspection_functions=1
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```
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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:
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──────
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event_date: 2019-11-20
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event_time: 2019-11-20 16:57:59
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revision: 54429
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timer_type: Real
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thread_number: 48
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query_id: 724028bf-f550-45aa-910d-2af6212b94ac
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trace: [94138803686098,94138815010911,94138815096522,94138815101224,94138815102091,94138814222988,94138806823642,94138814457211,94138806823642,94138814457211,94138806823642,94138806795179,94138806796144,94138753770094,94138753771646,94138753760572,94138852407232,140399185266395,140399178045583]
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```
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The `trace` field contains the stack trace at the moment of sampling.
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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:
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──────
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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
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```
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Applying the function to the whole stack trace:
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``` sql
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SELECT
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arrayStringConcat(arrayMap(x -> demangle(addressToSymbol(x)), trace), '\n') AS trace_functions
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FROM system.trace_log
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LIMIT 1
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\G
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```
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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:
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──────
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trace_functions: DB::IAggregateFunctionHelper<DB::AggregateFunctionSum<unsigned long, unsigned long, DB::AggregateFunctionSumData<unsigned long> > >::addBatchSinglePlace(unsigned long, char*, DB::IColumn const**, DB::Arena*) const
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DB::Aggregator::executeWithoutKeyImpl(char*&, unsigned long, DB::Aggregator::AggregateFunctionInstruction*, DB::Arena*) const
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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&)
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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&)
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DB::Aggregator::execute(std::shared_ptr<DB::IBlockInputStream> const&, DB::AggregatedDataVariants&)
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DB::AggregatingBlockInputStream::readImpl()
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DB::IBlockInputStream::read()
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DB::ExpressionBlockInputStream::readImpl()
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DB::IBlockInputStream::read()
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DB::ExpressionBlockInputStream::readImpl()
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DB::IBlockInputStream::read()
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DB::AsynchronousBlockInputStream::calculate()
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std::_Function_handler<void (), DB::AsynchronousBlockInputStream::next()::{lambda()#1}>::_M_invoke(std::_Any_data const&)
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ThreadPoolImpl<ThreadFromGlobalPool>::worker(std::_List_iterator<ThreadFromGlobalPool>)
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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
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ThreadPoolImpl<std::thread>::worker(std::_List_iterator<std::thread>)
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execute_native_thread_routine
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start_thread
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clone
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```
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## tid {#tid}
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Returns id of the thread, in which current [Block](https://clickhouse.tech/docs/en/development/architecture/#block) is processed.
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**Syntax**
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``` sql
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tid()
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```
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**Returned value**
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- Current thread id. [Uint64](../../sql-reference/data-types/int-uint.md#uint-ranges).
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**Example**
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Query:
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``` sql
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SELECT tid();
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```
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Result:
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``` text
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┌─tid()─┐
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│ 3878 │
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└───────┘
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```
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## logTrace {#logtrace}
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Emits trace log message to server log for each [Block](https://clickhouse.tech/docs/en/development/architecture/#block).
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**Syntax**
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``` sql
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logTrace('message')
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```
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**Arguments**
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- `message` — Message that is emitted to server log. [String](../../sql-reference/data-types/string.md#string).
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**Returned value**
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- Always returns 0.
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**Example**
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Query:
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``` sql
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SELECT logTrace('logTrace message');
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```
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Result:
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``` text
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┌─logTrace('logTrace message')─┐
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│ 0 │
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└──────────────────────────────┘
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```
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[Original article](https://clickhouse.tech/docs/en/query_language/functions/introspection/) <!--hide-->
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