Add explaination about tidb_allow_batch_cop#3265
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Signed-off-by: JaySon-Huang <tshent@qq.com>
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@JaySon-Huang 这个 PR 是否为 docs-special-week 的 PR 呢？如果是，请将 branch rebase 到 docs-special-week。 |
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@TomShawn 有一个新功能开发完，在4.0GA会带出去，但是之前没有补充相关的文档说明。没有在 special-week 原计划内。 |
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May 22, 2020
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| 2. 开启聚合推过 JOIN / UNION 等 TiDB 算子的优化： | ||
| 2. 开启 Super batch 功能： | ||
| 这个变量用来设置从 TiFlash 读取时，是否把 region 的请求进行合并。当查询中涉及的 region 数量比较大，可以尝试设置该变量为 1：对带 aggregation 的 TiFlash coprocess 请求生效；设置该变量为 2：对全部的 TiFlash coprocessor 请求生效。 |
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这个变量是什么变量呢？请明确写出变量名，最好能附上tidb-specific-system-variables.md里的链接。- region 的首字母为大写。
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| 4. 尝试开启 `Distince` 推过 `Join` / `Union` 等 TiDB 算子的优化： | ||
| 这个变量用来设置优化器是否执行带有 `Distinct` 的聚合函数（比如 `select count(distinct a) from t`）下推到 Coprocessor 的优化操作。 |
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这个变量是什么变量呢？请明确写出变量名，最好能附上 tidb-specific-system-variables.md 里的链接。
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| 4. 尝试开启 `Distince` 推过 `Join` / `Union` 等 TiDB 算子的优化： | ||
| 这个变量用来设置优化器是否执行带有 `Distinct` 的聚合函数（比如 `select count(distinct a) from t`）下推到 Coprocessor 的优化操作。 | ||
| 当查询中带有 `Distinct` 的聚合操作执行很慢时，可以尝试设置该变量为 `1`。 |
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如需换行，请在两行之间插入空行，否则会显示无换行。
Co-authored-by: TomShawn <41534398+TomShawn@users.noreply.github.com>
Signed-off-by: JaySon-Huang <tshent@qq.com>
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@TomShawn, @hanfei1991, PTAL. |
hanfei1991
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May 25, 2020
JaySon-Huang
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May 25, 2020
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LGTM |
yikeke
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May 26, 2020
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/merge |
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/run-all-tests |
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May 27, 2020
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/run-cherry-picker |
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cherry pick to release-4.0 in PR #3403 |
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Signed-off-by: JaySon-Huang tshent@qq.com
What is changed, added or deleted? (Required)
Add explaination about a new system variable
tidb_allow_batch_copto tidb-specific-variables.md and tiflash/tune-tiflash-performance.mdWhich TiDB version(s) do your changes apply to? (Required)
What is the related PR or file link(s)?