releases: add release notes for v8.4.0

[Oreoxmt]

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releases: add release notes for v8.4.0

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For details, see tips for choosing the affected versions (in Chinese).

• master (the latest development version)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.2 (TiDB 8.2 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions))

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• This PR is translated from: releases: add release notes for v8.4.0 docs-cn#18556
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• Delete files
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[ti-chi-bot]

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[hfxsd]

Suggested change

	| tidb_enable_table_partition | Deprecated | Always set to `ON`. Table partitioning has been GA since v5.1 and this experimental flag, if set to `OFF`, would cause create table with partitioning, just parse and ignore the partitioning clause. |
	| tidb_enable_list_partition | Deprecated | Always set to ON. List partitioning has been GA since v6.1 |
	| tidb_enable_global_index | Deprecated | Always set to `ON`. Global Index for partitioned tables is GA since v8.4.0, and needs explicit `GLOBAL` IndexOption to be used, so this system variable is no longer needed. |
	| [`tidb_enable_global_index`](/system-variables.md#tidb_enable_global_index-new-in-v760) | Deprecated | In v8.4.0, this variable is deprecated. Its value will be fixed to the default value `ON`, that is, [global index] is enabled by default (/partitioned-table.md#global-indexes). You only need to add the keyword `GLOBAL` to the corresponding column when executing `CREATE TABLE` or `ALTER TABLE` to create a global index. |
	| [`tidb_enable_list_partition`](/system-variables.md#tidb_enable_list_partition-new-in-v50) | Deprecated | In v8.4.0, this variable is deprecated. Its value will be fixed to the default value `ON`, that is, [list partitioning] is enabled by default (/partitioned-table.md#list-partitioning). |
	| [`tidb_enable_table_partition`](/system-variables.md#tidb_enable_table_partition) | Deprecated | In v8.4.0, this variable is deprecated. Its value will be fixed to the default value `ON`, that is, [table partitioning] is enabled by default (/partitioned-table.md). |
	| [`tidb_scatter_region`](/system-variables.md#tidb_scatter_region) | Modified | Originally it was boolean, only supports `ON` and `OFF`, and the Region of the newly created table only supports table level scattering after it is enabled. Starting from v8.4.0, the `SESSION` scope is added, the type is changed from boolean to enumeration, the default value is changed from `OFF` to null, and the optional values `TABLE` and `GLOBAL` are added. Supports cluster-level scattering policy to avoid the TiKV OOM issues caused by uneven distribution of regions during fast batch table creation.|
	| [`tidb_schema_cache_size`](/system-variables.md#tidb_schema_cache_size-new-in-v800) | Modified | Changes the default value from `0` to `536870912` (512 MiB) to indicate that the feature is enabled by default and the minimum value allowed is set to `67108864` (64 MiB). |
	| [`tidb_opt_prefer_range_scan`](/system-variables.md#tidb_opt_prefer_range_scan-new-in-v50) | Modified | Starting from v8.4.0, the default value of this variable is changed from `OFF` to `ON`. For tables with no statistics (pseudo-statistics) or empty tables (zero statistics), the optimiser prefers interval scans over full table scans.|

[hfxsd]

Suggested change

	| -------- | -------- | -------- | -------- |
	| -------- | -------- | -------- | -------- |
	| TiDB | [`grpc-keepalive-time`](/tidb-configuration-file.md#grpc-keepalive-time) | Modified | Adds the minimum value of `1'. |
	| TiDB | [`grpc-keepalive-timeout`](/tidb-configuration-file.md#grpc-keepalive-timeout) | Modified | This configuration file parameter was originally of INT type, and the minimum value was only supported to be set to `1`. Starting from v8.4.0, the data type is changed to FLOAT64 and the minimum value is set to `0.05`. You can decrease the value to reduce the performance impact of network jitter by reducing the retry interval in scenarios where network jitter is more frequent. |
	| TiKV | [`region-split-keys`](/tikv-configuration-file.md#region-split-keys) | Modified | Starting from v8.4.0, the default value is changed to `"2560000"`. Before v8.4.0, the default value is `"960000"`. |
	| TiKV | [`region-split-size`](/tikv-configuration-file.md#region-split-size) | Modified | Starting from v8.4.0, the default value is changed to `"256MiB"`. Before v8.4.0, the default value is `"96MiB"`. |
	| TiKV | [`sst-max-size`](/tikv-configuration-file.md#sst-max-size) | Modified | Starting from v8.4.0, the default value is changed to `"384MiB"`. Before v8.4.0, the default value is `"144MiB"`. |

[hfxsd]

Suggested change

	* Starting from v6.3.0, partitioned tables use [dynamic pruning mode](/partitioned-table.md#dynamic-pruning-mode) by default. Compared with static pruning mode, dynamic pruning mode supports features such as IndexJoin and plan cache with better performance. Therefore, static pruning mode will be deprecated.

[Frank945946]

LGTM

[qiancai]

Suggested change

	<td>In high-concurrency scenarios, you can use this feature to reduce the wait time for obtaining TSO and improve the cluster throughput.</td>
	<td>In high-concurrency scenarios, retr to reduce the wait time for obtaining TSO and improve the cluster throughput.</td>

[ti-chi-bot]

@Oreoxmt: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-verify	a751e1a	link	true	/test pull-verify

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[Frank945946]

LGTM

[ti-chi-bot]

@Frank945946: adding LGTM is restricted to approvers and reviewers in OWNERS files.

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