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Merge pull request #40473 from den-crane/patch-37

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Doc. Some notes about insert deduplication
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Alexey Milovidov 2022-08-22 02:52:36 +03:00 committed by GitHub
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docs/en/operations/settings/merge-tree-settings.md
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@ -135,7 +135,7 @@ Possible values:
Default value: 100.
The `Insert` command creates one or more blocks (parts). For [insert deduplication](../../engines/table-engines/mergetree-family/replication/), when writing into replicated tables, ClickHouse writes the hash sums of the created parts into ClickHouse Keeper. Hash sums are stored only for the most recent `replicated_deduplication_window` blocks. The oldest hash sums are removed from ClickHouse Keeper.
The `Insert` command creates one or more blocks (parts). For [insert deduplication](../../engines/table-engines/mergetree-family/replication.md), when writing into replicated tables, ClickHouse writes the hash sums of the created parts into ClickHouse Keeper. Hash sums are stored only for the most recent `replicated_deduplication_window` blocks. The oldest hash sums are removed from ClickHouse Keeper.
A large number of `replicated_deduplication_window` slows down `Inserts` because it needs to compare more entries.
The hash sum is calculated from the composition of the field names and types and the data of the inserted part (stream of bytes).
@ -164,6 +164,8 @@ Default value: 604800 (1 week).
Similar to [replicated_deduplication_window](#replicated-deduplication-window), `replicated_deduplication_window_seconds` specifies how long to store hash sums of blocks for insert deduplication. Hash sums older than `replicated_deduplication_window_seconds` are removed from ClickHouse Keeper, even if they are less than ` replicated_deduplication_window`.
The time is relative to the time of the most recent record, not to the wall time. If it's the only record it will be stored forever.
## max_replicated_logs_to_keep
How many records may be in the ClickHouse Keeper log if there is inactive replica. An inactive replica becomes lost when when this number exceed.

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docs/en/operations/settings/settings.md
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@ -1253,7 +1253,9 @@ Possible values:
Default value: 1.
By default, blocks inserted into replicated tables by the `INSERT` statement are deduplicated (see [Data Replication](../../engines/table-engines/mergetree-family/replication.md)).
By default, blocks inserted into replicated tables by the `INSERT` statement are deduplicated (see [Data Replication](../../engines/table-engines/mergetree-family/replication.md)).
For the replicated tables by default the only 100 of the most recent blocks for each partition are deduplicated (see [replicated_deduplication_window](merge-tree-settings.md#replicated-deduplication-window), [replicated_deduplication_window_seconds](merge-tree-settings.md/#replicated-deduplication-window-seconds)).
For not replicated tables see [non_replicated_deduplication_window](merge-tree-settings.md/#non-replicated-deduplication-window).
## deduplicate_blocks_in_dependent_materialized_views {#settings-deduplicate-blocks-in-dependent-materialized-views}
@ -1287,6 +1289,9 @@ Default value: empty string (disabled)
`insert_deduplication_token` is used for deduplication _only_ when not empty.
For the replicated tables by default the only 100 of the most recent inserts for each partition are deduplicated (see [replicated_deduplication_window](merge-tree-settings.md#replicated-deduplication-window), [replicated_deduplication_window_seconds](merge-tree-settings.md/#replicated-deduplication-window-seconds)).
For not replicated tables see [non_replicated_deduplication_window](merge-tree-settings.md/#non-replicated-deduplication-window).
Example:
```sql