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84 lines
5.2 KiB
Markdown
84 lines
5.2 KiB
Markdown
---
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slug: /en/operations/system-tables/part_log
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---
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# part_log
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The `system.part_log` table is created only if the [part_log](../../operations/server-configuration-parameters/settings.md#part-log) server setting is specified.
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This table contains information about events that occurred with [data parts](../../engines/table-engines/mergetree-family/custom-partitioning-key.md) in the [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) family tables, such as adding or merging data.
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The `system.part_log` table contains the following columns:
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- `hostname` ([LowCardinality(String)](../../sql-reference/data-types/string.md)) — Hostname of the server executing the query.
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- `query_id` ([String](../../sql-reference/data-types/string.md)) — Identifier of the `INSERT` query that created this data part.
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- `event_type` ([Enum8](../../sql-reference/data-types/enum.md)) — Type of the event that occurred with the data part. Can have one of the following values:
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- `NewPart` — Inserting of a new data part.
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- `MergeParts` — Merging of data parts.
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- `DownloadPart` — Downloading a data part.
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- `RemovePart` — Removing or detaching a data part using [DETACH PARTITION](../../sql-reference/statements/alter/partition.md#alter_detach-partition).
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- `MutatePart` — Mutating of a data part.
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- `MovePart` — Moving the data part from the one disk to another one.
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- `merge_reason` ([Enum8](../../sql-reference/data-types/enum.md)) — The reason for the event with type `MERGE_PARTS`. Can have one of the following values:
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- `NotAMerge` — The current event has the type other than `MERGE_PARTS`.
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- `RegularMerge` — Some regular merge.
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- `TTLDeleteMerge` — Cleaning up expired data.
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- `TTLRecompressMerge` — Recompressing data part with the.
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- `merge_algorithm` ([Enum8](../../sql-reference/data-types/enum.md)) — Merge algorithm for the event with type `MERGE_PARTS`. Can have one of the following values:
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- `Undecided`
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- `Horizontal`
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- `Vertical`
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- `event_date` ([Date](../../sql-reference/data-types/date.md)) — Event date.
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- `event_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — Event time.
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- `event_time_microseconds` ([DateTime64](../../sql-reference/data-types/datetime64.md)) — Event time with microseconds precision.
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- `duration_ms` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Duration.
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- `database` ([String](../../sql-reference/data-types/string.md)) — Name of the database the data part is in.
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- `table` ([String](../../sql-reference/data-types/string.md)) — Name of the table the data part is in.
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- `part_name` ([String](../../sql-reference/data-types/string.md)) — Name of the data part.
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- `partition_id` ([String](../../sql-reference/data-types/string.md)) — ID of the partition that the data part was inserted to. The column takes the `all` value if the partitioning is by `tuple()`.
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- `path_on_disk` ([String](../../sql-reference/data-types/string.md)) — Absolute path to the folder with data part files.
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- `rows` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The number of rows in the data part.
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- `size_in_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Size of the data part in bytes.
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- `merged_from` ([Array(String)](../../sql-reference/data-types/array.md)) — An array of names of the parts which the current part was made up from (after the merge).
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- `bytes_uncompressed` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Size of uncompressed bytes.
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- `read_rows` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The number of rows was read during the merge.
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- `read_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The number of bytes was read during the merge.
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- `peak_memory_usage` ([Int64](../../sql-reference/data-types/int-uint.md)) — The maximum difference between the amount of allocated and freed memory in context of this thread.
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- `error` ([UInt16](../../sql-reference/data-types/int-uint.md)) — The code number of the occurred error.
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- `exception` ([String](../../sql-reference/data-types/string.md)) — Text message of the occurred error.
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The `system.part_log` table is created after the first inserting data to the `MergeTree` table.
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**Example**
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``` sql
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SELECT * FROM system.part_log LIMIT 1 FORMAT Vertical;
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```
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``` text
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Row 1:
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──────
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hostname: clickhouse.eu-central1.internal
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query_id: 983ad9c7-28d5-4ae1-844e-603116b7de31
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event_type: NewPart
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merge_reason: NotAMerge
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merge_algorithm: Undecided
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event_date: 2021-02-02
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event_time: 2021-02-02 11:14:28
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event_time_microseconds: 2021-02-02 11:14:28.861919
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duration_ms: 35
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database: default
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table: log_mt_2
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part_name: all_1_1_0
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partition_id: all
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path_on_disk: db/data/default/log_mt_2/all_1_1_0/
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rows: 115418
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size_in_bytes: 1074311
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merged_from: []
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bytes_uncompressed: 0
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read_rows: 0
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read_bytes: 0
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peak_memory_usage: 0
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error: 0
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exception:
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```
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