perf-tuning: add column-prune.md (#3246)#3316
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toutdesuite merged 4 commits intoJul 20, 2020
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@toutdesuite please accept the invitation then you can push to the cherry-pick pull requests. |
TomShawn
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| - [TiDB Troubleshooting Map](/tidb-troubleshooting-map.md) | ||
| - [Troubleshoot Cluster Setup](/troubleshoot-tidb-cluster.md) | ||
| - [Troubleshoot TiDB Lightning](/troubleshoot-tidb-lightning.md) | ||
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@toutdesuite Please resolve the conflict. Be careful about the version difference.
TomShawn
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Jul 20, 2020
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| In this query, only column a and column b are used, and column c and column d are redundant. Regarding the query plan of this statement, the `Selection` operator uses column b. Then the `DataSource` operator uses columns a and column b. Columns c and column d can be pruned because the `DataSource` operator does not read them. | ||
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| Therefore, when TiDB performs a top-down scanning during the logic optimization phase, redundant columns are pruned to reduce waste of resources. This scanning process is called "Column Pruning", corresponding to the `columnPruner` rule. If you want to disable this rule, refer to [The Blocklist of Optimization Rules and Expression Pushdown](/blocklist-control-plan.md). |
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| Therefore, when TiDB performs a top-down scanning during the logic optimization phase, redundant columns are pruned to reduce waste of resources. This scanning process is called "Column Pruning", corresponding to the `columnPruner` rule. If you want to disable this rule, refer to [The Blocklist of Optimization Rules and Expression Pushdown](/blocklist-control-plan.md). | |
| Therefore, when TiDB performs a top-down scanning during the logic optimization phase, redundant columns are pruned to reduce waste of resources. This scanning process is called "Column Pruning", corresponding to the `columnPruner` rule. If you want to disable this rule, refer to [The Blocklist of Optimization Rules and Expression Pushdown](https://docs.pingcap.com/tidb/dev/blocklist-control-plan). |
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Shall we delete this sentence? Refer to https://github.com/pingcap/docs-cn/blob/release-2.1/column-pruning.md
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But users might wonder how to disable this rule.
toutdesuite
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Jul 20, 2020
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cherry-pick #3246 to release-2.1
What is changed, added or deleted? (Required)
add column-prune.md
Merge #3043 to fix CI failure
Which TiDB version(s) do your changes apply to? (Required)
What is the related PR or file link(s)?