Introspection Functions

Documentation for Introspection Functions

You can use functions described in this chapter to introspect ELF and DWARF for query profiling.

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 setting to 1.

  For security reasons introspection functions are disabled by default.

ClickHouse saves profiler reports to the trace_log system table. Make sure the table and profiler are configured properly.

addressToLine

Introduced in: v20.1.0

Converts a virtual memory address inside the ClickHouse server process to a filename and line number in ClickHouse’s source code.

This function is slow and may impose security considerations.

To enable this introspection function:

• Install the clickhouse-common-static-dbg package.
• Set setting allow_introspection_functions to 1.

Syntax

addressToLine(address_of_binary_instruction)

Arguments

• address_of_binary_instruction — Address of instruction in a running process. UInt64

Returned value

Returns a source code filename and line number delimited by a colon, for example, /build/obj-x86_64-linux-gnu/../src/Common/ThreadPool.cpp:199. Returns the name of a binary, if no debug information could be found, otherwise an empty string, if the address is not valid. String

Examples

Selecting the first string from the trace_log system table

Query

SET allow_introspection_functions=1;
SELECT * FROM system.trace_log LIMIT 1 \G;

Response

-- The `trace` field contains the stack trace at the moment of sampling.
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]

Getting the source code filename and the line number for a single address

Query

SET allow_introspection_functions=1;
SELECT addressToLine(94784076370703) \G;

Response

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

Applying the function to the whole stack trace

Query

-- The arrayMap function in this example processing each individual element of the trace array by the addressToLine function.
-- The result of this processing is seen in the trace_source_code_lines column of output.

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

Response

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

Introduced in: v22.2.0

Similar to addressToLine, but returns an Array with all inline functions. As a result of this, it is slower than addressToLine.

To enable this introspection function:

• Install the clickhouse-common-static-dbg package.
• Set setting allow_introspection_functions to 1.

Syntax

addressToLineWithInlines(address_of_binary_instruction)

Arguments

• address_of_binary_instruction — The address of an instruction in a running process. UInt64

Returned value

Returns an array whose first element is the source code filename and line number delimited by a colon. The second, third, etc. element list inline functions’ source code filenames, line numbers and function names. If no debug information could be found, 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)

Examples

Applying the function to an address

Query

SET allow_introspection_functions=1;
SELECT addressToLineWithInlines(531055181::UInt64);

Response

┌─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

Query

SET allow_introspection_functions=1;

-- The arrayJoin function will split array to rows

SELECT
    ta, addressToLineWithInlines(arrayJoin(trace) AS ta)
FROM system.trace_log
WHERE
    query_id = '5e173544-2020-45de-b645-5deebe2aae54';

Response

┌────────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

Introduced in: v20.1.0

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

Syntax

addressToSymbol(address_of_binary_instruction)

Arguments

• address_of_binary_instruction — Address of instruction in a running process. UInt64

Returned value

Returns the symbol from ClickHouse object files or an empty string, if the address is not valid. String

Examples

Selecting the first string from the trace_log system table

Query

SET allow_introspection_functions=1;
SELECT * FROM system.trace_log LIMIT 1 \G;

Response

-- The `trace` field contains the stack trace at the moment of sampling.
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]

Getting a symbol for a single address

Query

SET allow_introspection_functions=1;
SELECT addressToSymbol(94138803686098) \G;

Response

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

Applying the function to the whole stack trace

Query

SET allow_introspection_functions=1;

-- The arrayMap function allows to process each individual element of the trace array by the addressToSymbols function.
-- The result of this processing is shown in the trace_symbols column of output.

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

Response

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

Introduced in: v20.1.0

Converts a symbol to a C++ function name. The symbol is usually returned by function addressToSymbol.

Syntax

demangle(symbol)

Arguments

• symbol — Symbol from an object file. String

Returned value

Returns the name of the C++ function, or an empty string if the symbol is not valid. String

Examples

Selecting the first string from the trace_log system table

Query

SELECT * FROM system.trace_log LIMIT 1 \G;

Response

-- The `trace` field contains the stack trace at the moment of sampling.
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]

Getting a function name for a single address

Query

SET allow_introspection_functions=1;
SELECT demangle(addressToSymbol(94138803686098)) \G;

Response

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

Query

SET allow_introspection_functions=1;

-- The arrayMap function allows to process each individual element of the trace array by the demangle function.
-- The result of this processing is shown in the trace_functions column of output.

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

Response

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(...)
DB::Aggregator::executeOnBlock(DB::Block const&, ...)
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

isMergeTreePartCoveredBy

Introduced in: v25.6.0

Function which checks if the part of the first argument is covered by the part of the second argument.

Syntax

isMergeTreePartCoveredBy(nested_part, covering_part)

Arguments

• nested_part — Name of expected nested part. String
• covering_part — Name of expected covering part. String

Returned value

Returns 1 if it covers, 0 otherwise. UInt8

Examples

Basic example

Query

WITH 'all_12_25_7_4' AS lhs, 'all_7_100_10_20' AS rhs
SELECT isMergeTreePartCoveredBy(rhs, lhs), isMergeTreePartCoveredBy(lhs, rhs);

Response

┌─isMergeTreePartCoveredBy(rhs, lhs)─┬─isMergeTreePartCoveredBy(lhs, rhs)─┐
│                                  0 │                                  1 │
└────────────────────────────────────┴────────────────────────────────────┘

logTrace

Introduced in: v20.12.0

Emits a trace log message to the server log.

The function accepts a constant argument only, so the call is evaluated during query analysis and replaced by its result. The message is therefore emitted once while the query is analyzed, and not once per processed Block: the number of rows and the setting max_block_size have no effect on how many messages appear in the log.

Syntax

logTrace(message)

Arguments

• message — Message that is emitted to the server log. const String

Returned value

Returns 0 always. UInt8

Examples

Basic example

Query

SELECT logTrace('logTrace message');

Response

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

mergeTreePartInfo

Introduced in: v25.6.0

Function that helps to cut the useful values out of the MergeTree part name.

Syntax

mergeTreePartInfo(part_name)

Arguments

• part_name — Name of part to unpack. String

Returned value

Returns a Tuple with subcolumns: partition_id, min_block, max_block, level, mutation. Tuple

Examples

Basic example

Query

WITH mergeTreePartInfo('all_12_25_7_4') AS info
SELECT info.partition_id, info.min_block, info.max_block, info.level, info.mutation;

Response

┌─info.partition_id─┬─info.min_block─┬─info.max_block─┬─info.level─┬─info.mutation─┐
│ all               │             12 │             25 │          7 │             4 │
└───────────────────┴────────────────┴────────────────┴────────────┴───────────────┘

tid

Introduced in: v20.12.0

Returns id of the thread, in which the current Block is processed.

Syntax

tid()

Arguments

• None.

Returned value

Returns the current thread id. UInt64

Examples

Usage example

Query

SELECT tid();

Response

┌─tid()─┐
│  3878 │
└───────┘