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Posted to commits@doris.apache.org by GitBox <gi...@apache.org> on 2022/10/31 14:05:09 UTC
[GitHub] [doris] spaces-X opened a new pull request, #13842: [doc](prefix-index): add the limit rule on the num of key columns in prefix index
spaces-X opened a new pull request, #13842:
URL: https://github.com/apache/doris/pull/13842
# Proposed changes
fix doc of prefix index
## Problem summary
Describe your changes.
## Checklist(Required)
1. Does it affect the original behavior:
- [ ] Yes
- [ ] No
- [ ] I don't know
2. Has unit tests been added:
- [ ] Yes
- [ ] No
- [ ] No Need
3. Has document been added or modified:
- [ ] Yes
- [ ] No
- [ ] No Need
4. Does it need to update dependencies:
- [ ] Yes
- [ ] No
5. Are there any changes that cannot be rolled back:
- [ ] Yes (If Yes, please explain WHY)
- [ ] No
## Further comments
If this is a relatively large or complex change, kick off the discussion at [dev@doris.apache.org](mailto:dev@doris.apache.org) by explaining why you chose the solution you did and what alternatives you considered, etc...
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[GitHub] [doris] yiguolei commented on a diff in pull request #13842: [doc](prefix-index): add the limit rule on the num of key columns in prefix index
Posted by GitBox <gi...@apache.org>.
yiguolei commented on code in PR #13842:
URL: https://github.com/apache/doris/pull/13842#discussion_r1012790878
##########
docs/zh-CN/docs/data-table/index/prefix-index.md:
##########
@@ -41,6 +41,23 @@ under the License.
而前缀索引，即在排序的基础上，实现的一种根据给定前缀列，快速查询数据的索引方式。
+需要注意的是为了防止索引膨胀，**在36字节限制和varchar截断限制的基础上，增加了列数限制（默认：3列）**，默认为**前三个KEY列**参与索引的构建，如果用户期望将更多的key列纳入到前缀索引中，需要在建表时修改PROPERTIES如下：
+
+```sql
+CREATE TABLE xxx
+(
+ ...
+)
+...
+PROPERTIES(
+ "shortkey_max_column_count" = "n" -- 其中 n 为用户设定的参与前缀索引构建的列数
Review Comment:
why do we need this limit? I think if user could set column count here, he could just set it to 100 and then he or she could use as many as columns in his alter sql.
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[GitHub] [doris] spaces-X commented on a diff in pull request #13842: [doc](prefix-index): add the limit rule on the num of key columns in prefix index
Posted by GitBox <gi...@apache.org>.
spaces-X commented on code in PR #13842:
URL: https://github.com/apache/doris/pull/13842#discussion_r1018759762
##########
docs/zh-CN/docs/data-table/index/prefix-index.md:
##########
@@ -41,6 +41,23 @@ under the License.
而前缀索引，即在排序的基础上，实现的一种根据给定前缀列，快速查询数据的索引方式。
+需要注意的是为了防止索引膨胀，**在36字节限制和varchar截断限制的基础上，增加了列数限制（默认：3列）**，默认为**前三个KEY列**参与索引的构建，如果用户期望将更多的key列纳入到前缀索引中，需要在建表时修改PROPERTIES如下：
+
+```sql
+CREATE TABLE xxx
+(
+ ...
+)
+...
+PROPERTIES(
+ "shortkey_max_column_count" = "n" -- 其中 n 为用户设定的参与前缀索引构建的列数
Review Comment:
From the last discussion in the wechat group, the conclusion is that the default value of this parameter is to prevent the short index from being too large if so the index filtering does not work well. But the default value is goot at all scenarios, so we make this parameter configurable.
The key point is that there is a difference between the description in the document and the implementation in the engine, which will cause confusion to users
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[GitHub] [doris] github-actions[bot] closed pull request #13842: [doc](prefix-index): add the limit rule on the num of key columns in prefix index
Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.
github-actions[bot] closed pull request #13842: [doc](prefix-index): add the limit rule on the num of key columns in prefix index
URL: https://github.com/apache/doris/pull/13842
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[GitHub] [doris] github-actions[bot] commented on pull request #13842: [doc](prefix-index): add the limit rule on the num of key columns in prefix index
Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.
github-actions[bot] commented on PR #13842:
URL: https://github.com/apache/doris/pull/13842#issuecomment-1541042404
We're closing this PR because it hasn't been updated in a while.
This isn't a judgement on the merit of the PR in any way. It's just a way of keeping the PR queue manageable.
If you'd like to revive this PR, please reopen it and feel free a maintainer to remove the Stale tag!
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[GitHub] [doris] hf200012 commented on pull request #13842: [doc](prefix-index): add the limit rule on the num of key columns in prefix index
Posted by GitBox <gi...@apache.org>.
hf200012 commented on PR #13842:
URL: https://github.com/apache/doris/pull/13842#issuecomment-1298666297
Create table syntax adds a description
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