ClickHouse/docs/en/operations/system-tables/processors_profile_log.md

system.processors_profile_log

This table contains profiling on processors level (that you can find in EXPLAIN PIPELINE).

Columns:

• event_date (Date) — The date when the event happened.
• event_time (DateTime64) — The date and time when the event happened.
• query_id (String) — ID of the query
• name (LowCardinality(String)) — Name of the processor.
• elapsed_us (UInt64) — Number of microseconds this processor was executed.
• input_wait_elapsed_us (UInt64) — Number of microseconds this processor was waiting for data (from other processor).
• output_wait_elapsed_us (UInt64) — Number of microseconds this processor was waiting because output port was full.

Example

Query:

EXPLAIN PIPELINE
SELECT sleep(1)

┌─explain─────────────────────────┐
│ (Expression)                    │
│ ExpressionTransform             │
│   (SettingQuotaAndLimits)       │
│     (ReadFromStorage)           │
│     SourceFromSingleChunk 0 → 1 │
└─────────────────────────────────┘

SELECT sleep(1)
SETTINGS log_processors_profiles = 1

Query id: feb5ed16-1c24-4227-aa54-78c02b3b27d4

┌─sleep(1)─┐
│        0 │
└──────────┘

1 rows in set. Elapsed: 1.018 sec.

SELECT
    name,
    elapsed_us,
    input_wait_elapsed_us,
    output_wait_elapsed_us
FROM system.processors_profile_log
WHERE query_id = 'feb5ed16-1c24-4227-aa54-78c02b3b27d4'
ORDER BY name ASC

Result:

┌─name────────────────────┬─elapsed_us─┬─input_wait_elapsed_us─┬─output_wait_elapsed_us─┐
│ ExpressionTransform     │    1000497 │                  2823 │                    197 │
│ LazyOutputFormat        │         36 │               1002188 │                      0 │
│ LimitsCheckingTransform │         10 │               1002994 │                    106 │
│ NullSource              │          5 │               1002074 │                      0 │
│ NullSource              │          1 │               1002084 │                      0 │
│ SourceFromSingleChunk   │         45 │                  4736 │                1000819 │
└─────────────────────────┴────────────┴───────────────────────┴────────────────────────┘

Here you can see:

• ExpressionTransform was executing sleep(1) function, so it work will takes 1e6, and so elapsed_us > 1e6.
• SourceFromSingleChunk need to wait, because ExpressionTransform does not accept any data during execution of sleep(1), so it will be in PortFull state for 1e6 us, and so output_wait_elapsed_us > 1e6.
• LimitsCheckingTransform/NullSource/LazyOutputFormat need to wait until ExpressionTransform will execute sleep(1) to process the result, so input_wait_elapsed_us > 1e6.

See Also

• EXPLAIN PIPELINE