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Document a few more system variables #6492

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Sep 30, 2021
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Document a few more system variables #6492

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7fea7a7
Document a few more system variables
dveeden Sep 16, 2021
b02e351
Plugin vars are instance scoped
dveeden Sep 16, 2021
696e734
Update system-variables.md
dveeden Sep 16, 2021
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Apply suggestions from code review
dveeden Sep 29, 2021
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Merge branch 'master' into missing_sysvars_2
TomShawn Sep 30, 2021
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41 changes: 41 additions & 0 deletions system-variables.md
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Expand Up @@ -250,6 +250,12 @@ mysql> SELECT * FROM t1;
- Default value: `Apache License 2.0`
- This variable indicates the license of your TiDB server installation.

### log_bin

- Scope: NONE
- Default value: `OFF`
- This variable indicates whether [TiDB Binlog](/tidb-binlog/tidb-binlog-overview.md) is used.

### max_allowed_packet

- Scope: GLOBAL | SESSION
Expand All @@ -269,6 +275,18 @@ mysql> SELECT * FROM t1;
>
> Unlike in MySQL, the `max_execution_time` system variable currently works on all kinds of statements in TiDB, not only restricted to the `SELECT` statement. The precision of the timeout value is roughly 100ms. This means the statement might not be terminated in accurate milliseconds as you specify.

### plugin_dir
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- Scope: INSTANCE
- Default value: ""
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pingcap/tidb#28084

- Indicates the directory to load plugins as specified by a command-line flag.

### plugin_load

- Scope: INSTANCE
- Default value: ""
- Indicates the plugins to load when TiDB is started. These plugins are specified by a command-line flag and separated by commas.

### port

- Scope: NONE
Expand Down Expand Up @@ -299,6 +317,16 @@ mysql> SELECT * FROM t1;
- Default value: ""
- The local unix socket file that the `tidb-server` is listening on when speaking the MySQL protocol.

### sql_log_bin
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pingcap/tidb#9159


- Scope: SESSION | GLOBAL
- Default value: `ON`
- Indicates whether to write changes to [TiDB Binlog](/tidb-binlog/tidb-binlog-overview.md) or not.

> **Note:**
>
> It is not recommended to set `sql_log_bin` as a global variable because the future versions of TiDB might only allow setting this as a session variable.

### sql_mode

- Scope: SESSION | GLOBAL
Expand Down Expand Up @@ -1480,6 +1508,19 @@ SET tidb_slow_log_threshold = 200;
- This variable returns the current time zone. Values can be specified as either an offset such as '-8:00' or a named zone 'America/Los_Angeles'.
- The value `SYSTEM` means that the time zone should be the same as the system host, which is available via the [`system_time_zone`](#system_time_zone) variable.

### timestamp

- Scope: SESSION
- Default value: ""
- A non-empty value of this variable indicates the UNIX epoch that is used as the timestamp for `CURRENT_TIMESTAMP()`, `NOW()`, and other functions. This variable might be used in data restore or replication.

### tmp_table_size
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This variable is deleted in #6775.


- Scope: SESSION | GLOBAL
- Default value: `16777216`
- Unit: Bytes
- Indicates the maximum size of a temporary table.

### transaction_isolation

- Scope: SESSION | GLOBAL
Expand Down