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

slug
/en/operations/system-tables/part_log

part_log

The system.part_log table is created only if the part_log server setting is specified.

This table contains information about events that occurred with data parts in the MergeTree family tables, such as adding or merging data.

The system.part_log table contains the following columns:

• hostname (LowCardinality(String)) — Hostname of the server executing the query.
• query_id (String) — Identifier of the INSERT query that created this data part.
• event_type (Enum8) — Type of the event that occurred with the data part. Can have one of the following values:
  • NewPart — Inserting of a new data part.
  • MergePartsStart — Merging of data parts has started.
  • MergeParts — Merging of data parts has finished.
  • DownloadPart — Downloading a data part.
  • RemovePart — Removing or detaching a data part using DETACH PARTITION.
  • MutatePartStart — Mutating of a data part has started.
  • MutatePart — Mutating of a data part has finished.
  • MovePart — Moving the data part from the one disk to another one.
• merge_reason (Enum8) — The reason for the event with type MERGE_PARTS. Can have one of the following values:
  • NotAMerge — The current event has the type other than MERGE_PARTS.
  • RegularMerge — Some regular merge.
  • TTLDeleteMerge — Cleaning up expired data.
  • TTLRecompressMerge — Recompressing data part with the.
• merge_algorithm (Enum8) — Merge algorithm for the event with type MERGE_PARTS. Can have one of the following values:
  • Undecided
  • Horizontal
  • Vertical
• event_date (Date) — Event date.
• event_time (DateTime) — Event time.
• event_time_microseconds (DateTime64) — Event time with microseconds precision.
• duration_ms (UInt64) — Duration.
• database (String) — Name of the database the data part is in.
• table (String) — Name of the table the data part is in.
• part_name (String) — Name of the data part.
• partition_id (String) — ID of the partition that the data part was inserted to. The column takes the all value if the partitioning is by tuple().
• path_on_disk (String) — Absolute path to the folder with data part files.
• rows (UInt64) — The number of rows in the data part.
• size_in_bytes (UInt64) — Size of the data part in bytes.
• merged_from (Array(String)) — An array of names of the parts which the current part was made up from (after the merge).
• bytes_uncompressed (UInt64) — Size of uncompressed bytes.
• read_rows (UInt64) — The number of rows was read during the merge.
• read_bytes (UInt64) — The number of bytes was read during the merge.
• peak_memory_usage (Int64) — The maximum difference between the amount of allocated and freed memory in context of this thread.
• error (UInt16) — The code number of the occurred error.
• exception (String) — Text message of the occurred error.

The system.part_log table is created after the first inserting data to the MergeTree table.

Example

SELECT * FROM system.part_log LIMIT 1 FORMAT Vertical;

Row 1:
──────
hostname:                      clickhouse.eu-central1.internal
query_id:                      983ad9c7-28d5-4ae1-844e-603116b7de31
event_type:                    NewPart
merge_reason:                  NotAMerge
merge_algorithm:               Undecided
event_date:                    2021-02-02
event_time:                    2021-02-02 11:14:28
event_time_microseconds:       2021-02-02 11:14:28.861919
duration_ms:                   35
database:                      default
table:                         log_mt_2
part_name:                     all_1_1_0
partition_id:                  all
path_on_disk:                  db/data/default/log_mt_2/all_1_1_0/
rows:                          115418
size_in_bytes:                 1074311
merged_from:                   []
bytes_uncompressed:            0
read_rows:                     0
read_bytes:                    0
peak_memory_usage:             0
error:                         0
exception: