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[fix](Export) fix description of data_consitency (apache#482)
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BePPPower authored Mar 29, 2024
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Expand Up @@ -96,7 +96,7 @@ The bottom layer of the `Export` statement actually executes the `select...outfi

- `with_bom`: The default is false. If it is set to true, the exported file is encoded in UTF8 with BOM (valid only for CSV-related file format).

- `data_consisteency`: can be set to` none` / ` partition`, default value is `none`. This parameter indicates the granularity at which the export table is shred, `none` represents tablets level, and` partition` represents partition level.
- `data_consistency`: can be set to` none` / `partition` , default value is `partition`. This parameter indicates the granularity at which the export table is shred, `none` represents tablets level, and` partition` represents partition level.

- `timeout`: This is the timeout parameter of the export job, the default timeout is 2 hours, and the unit is seconds.

Expand Down Expand Up @@ -349,7 +349,7 @@ WITH BROKER "broker_name"

#### Concurrent Export

An Export job can be configured with the `parallelism` parameter to concurrently export data. The `parallelism` parameter specifies the number of threads to execute the `EXPORT Job`. Each thread is responsible for exporting a subset of the total tablets.
An Export job can be configured with the `parallelism` parameter to concurrently export data. The `parallelism` parameter specifies the number of threads to execute the `EXPORT Job`. When you set `"data_consistency" = "none"` , each thread is responsible for exporting a subset of the total tablets.

The underlying execution logic of an `Export Job `is actually the `SELECT INTO OUTFILE` statement. Each thread specified by the `parallelism` parameter executes independent `SELECT INTO OUTFILE` statements.

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Expand Up @@ -92,7 +92,7 @@ EXPORT

- `with_bom`: 默认为false,若指定为true,则导出的文件编码为带有BOM的UTF8编码(只对csv相关的文件格式生效)。

- `data_consistency`: 可以设置为 `none` / `partition` ,默认为 `none` 。指示以何种粒度切分导出表,`none` 代表 Tablets 级别,`partition`代表 Partition 级别。
- `data_consistency`: 可以设置为 `none` / `partition` ,默认为 `partition` 。指示以何种粒度切分导出表,`none` 代表 Tablets 级别,`partition`代表 Partition 级别。

- `timeout`:导出作业的超时时间,默认为2小时,单位是秒。

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#### 并发执行

一个 Export 作业可以设置`parallelism`参数来并发导出数据。`parallelism`参数实际就是指定执行 EXPORT 作业的线程数量。每一个线程会负责导出表的部分Tablets。
一个 Export 作业可以设置`parallelism`参数来并发导出数据。`parallelism`参数实际就是指定执行 EXPORT 作业的线程数量。当设置`"data_consistency" = "none"`时,每一个线程会负责导出表的部分Tablets。

一个 Export 作业的底层执行逻辑实际上是`SELECT INTO OUTFILE`语句,`parallelism`参数设置的每一个线程都会去执行独立的`SELECT INTO OUTFILE`语句。

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