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Add documentation for insert_quorum_parallel.

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Christoph Wurm 2021-12-07 14:24:57 +00:00
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docs/en/operations/settings/settings.md
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@ -1707,18 +1707,17 @@ Quorum writes
`INSERT` succeeds only when ClickHouse manages to correctly write data to the `insert_quorum` of replicas during the `insert_quorum_timeout`. If for any reason the number of replicas with successful writes does not reach the `insert_quorum`, the write is considered failed and ClickHouse will delete the inserted block from all the replicas where data has already been written. `INSERT` succeeds only when ClickHouse manages to correctly write data to the `insert_quorum` of replicas during the `insert_quorum_timeout`. If for any reason the number of replicas with successful writes does not reach the `insert_quorum`, the write is considered failed and ClickHouse will delete the inserted block from all the replicas where data has already been written.
All the replicas in the quorum are consistent, i.e., they contain data from all previous `INSERT` queries. The `INSERT` sequence is linearized. When `insert_quorum_parallel` is disabled, all replicas in the quorum are consistent, i.e. they contain data from all previous `INSERT` queries (the `INSERT` sequence is linearized). When reading data written using `insert_quorum` and `insert_quorum_parallel` is disabled, you can turn on sequential consistency for `SELECT` queries using [select_sequential_consistency](#settings-select_sequential_consistency).
When reading the data written from the `insert_quorum`, you can use the [select_sequential_consistency](#settings-select_sequential_consistency) option. ClickHouse generates an exception:
ClickHouse generates an exception
- If the number of available replicas at the time of the query is less than the `insert_quorum`. - If the number of available replicas at the time of the query is less than the `insert_quorum`.
- At an attempt to write data when the previous block has not yet been inserted in the `insert_quorum` of replicas. This situation may occur if the user tries to perform an `INSERT` before the previous one with the `insert_quorum` is completed. - When `insert_quorum_parallel` is disabled and an attempt to write data is made when the previous block has not yet been inserted in `insert_quorum` of replicas. This situation may occur if the user tries to perform an `INSERT` before the previous one with `insert_quorum` is completed.
See also: See also:
- [insert_quorum_timeout](#settings-insert_quorum_timeout) - [insert_quorum_timeout](#settings-insert_quorum_timeout)
- [insert_quorum_parallel](#settings-insert_quorum_parallel)
- [select_sequential_consistency](#settings-select_sequential_consistency) - [select_sequential_consistency](#settings-select_sequential_consistency)
## insert_quorum_timeout {#settings-insert_quorum_timeout} ## insert_quorum_timeout {#settings-insert_quorum_timeout}
@ -1730,11 +1729,29 @@ Default value: 600 000 milliseconds (ten minutes).
See also: See also:
- [insert_quorum](#settings-insert_quorum) - [insert_quorum](#settings-insert_quorum)
- [insert_quorum_parallel](#settings-insert_quorum_parallel)
- [select_sequential_consistency](#settings-select_sequential_consistency)
## insert_quorum_parallel {#settings-insert_quorum_parallel}
Enables or disables parallelism for quorum `INSERT` queries. If enabled, additional `INSERT` queries can be sent while previous queries have not yet finished. If disabled, additional queries will be rejected.
Possible values:
- 0 — Disabled.
- 1 — Enabled.
Default value: 1.
See also:
- [insert_quorum](#settings-insert_quorum)
- [insert_quorum_timeout](#settings-insert_quorum_timeout)
- [select_sequential_consistency](#settings-select_sequential_consistency) - [select_sequential_consistency](#settings-select_sequential_consistency)
## select_sequential_consistency {#settings-select_sequential_consistency} ## select_sequential_consistency {#settings-select_sequential_consistency}
Enables or disables sequential consistency for `SELECT` queries: Enables or disables sequential consistency for `SELECT` queries. Requires `insert_quorum_parallel` to be disabled (enabled by default).
Possible values: Possible values:
@ -1747,10 +1764,13 @@ Usage
When sequential consistency is enabled, ClickHouse allows the client to execute the `SELECT` query only for those replicas that contain data from all previous `INSERT` queries executed with `insert_quorum`. If the client refers to a partial replica, ClickHouse will generate an exception. The SELECT query will not include data that has not yet been written to the quorum of replicas. When sequential consistency is enabled, ClickHouse allows the client to execute the `SELECT` query only for those replicas that contain data from all previous `INSERT` queries executed with `insert_quorum`. If the client refers to a partial replica, ClickHouse will generate an exception. The SELECT query will not include data that has not yet been written to the quorum of replicas.
When `insert_quorum_parallel` is enabled (the default), then `select_sequential_consistency` does not work. This is because parallel `INSERT` queries can be written to different sets of quorum replicas so there is no guarantee a single replica will have received all writes.
See also: See also:
- [insert_quorum](#settings-insert_quorum) - [insert_quorum](#settings-insert_quorum)
- [insert_quorum_timeout](#settings-insert_quorum_timeout) - [insert_quorum_timeout](#settings-insert_quorum_timeout)
- [insert_quorum_parallel](#settings-insert_quorum_parallel)
## insert_deduplicate {#settings-insert-deduplicate} ## insert_deduplicate {#settings-insert-deduplicate}