99 lines
3.2 KiB
Markdown
99 lines
3.2 KiB
Markdown
---
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{
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"title": "Colocate Join",
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"language": "en"
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}
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---
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<!--
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Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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# Colocate Join
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## Description
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Colocate/Local Join means that when multiple nodes are Join, there is no data movement and network transmission, and each node is only Join locally.
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The premise of Join locally is to import data from the same Join Key into a fixed node according to the same rules.
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1 How To Use:
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Simply add the property colocate_with when building a table. The value of colocate_with can be set to any one of the same set of colocate tables.
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However, you need to ensure that tables in the colocate_with attribute are created first.
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If you need to Colocate Join table t1 and t2, you can build tables according to the following statements:
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CREATE TABLE `t1` (
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`id` int(11) COMMENT "",
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'value ` varchar (8) COMMENT ""
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) ENGINE=OLAP
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DUPLICATE KEY(`id`)
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DISTRIBUTED BY HASH(`id`) BUCKETS 10
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PROPERTIES (
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"colocate_with" = "t1"
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);
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CREATE TABLE `t2` (
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`id` int(11) COMMENT "",
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'value ` varchar (8) COMMENT ""
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) ENGINE=OLAP
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DUPLICATE KEY(`id`)
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DISTRIBUTED BY HASH(`id`) BUCKETS 10
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PROPERTIES (
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"colocate_with" = "t1"
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);
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2 Colocate Join 目前的限制:
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1. Colcoate Table must be an OLAP-type table
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2. The BUCKET number of tables with the same colocate_with attribute must be the same
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3. The number of copies of tables with the same colocate_with attribute must be the same
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4. Data types of DISTRIBUTTED Columns for tables with the same colocate_with attribute must be the same
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3 Colocate Join's applicable scenario:
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Colocate Join is well suited for scenarios where tables are bucketed according to the same field and high frequency according to the same field Join.
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4 FAQ:
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Q: 支持多张表进行Colocate Join 吗?
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A: 25903;. 25345
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Q: Do you support Colocate table and normal table Join?
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A: 25903;. 25345
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Q: Does the Colocate table support Join with non-bucket Key?
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A: Support: Join that does not meet Colocate Join criteria will use Shuffle Join or Broadcast Join
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Q: How do you determine that Join is executed according to Colocate Join?
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A: The child node of Hash Join in the result of explain is Colocate Join if it is OlapScanNode directly without Exchange Node.
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Q: How to modify the colocate_with attribute?
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A: ALTER TABLE example_db.my_table set ("colocate_with"="target_table");
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Q: 229144; colcoate join?
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A: set disable_colocate_join = true; 就可以禁用Colocate Join，查询时就会使用Shuffle Join 和Broadcast Join
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## keyword
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COLOCATE, JOIN, CREATE TABLE
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