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Posted to commits@doris.apache.org by GitBox <gi...@apache.org> on 2020/10/08 12:22:26 UTC
[GitHub] [incubator-doris] HappenLee opened a new issue #4706: [Proposal] Support Limit Clause Push Down For ODBC Table And MySQL Table
HappenLee opened a new issue #4706:
URL: https://github.com/apache/incubator-doris/issues/4706
## Motivation
At present, Doris do not push down **limit operation** to Exteranl Table Engine.It may serious performance problems in some scenarios. For example, this is a Exteranl Table of Mysql:
```
CREATE EXTERNAL TABLE `baseall_mysql` (
`k1` tinyint(4) NULL COMMENT "",
`k2` smallint(6) NULL COMMENT "",
`k3` int(11) NULL COMMENT "",
`k4` bigint(20) NULL COMMENT "",
`k5` decimal(9, 3) NULL COMMENT "",
`k6` char(5) NULL COMMENT "",
`k10` date NULL COMMENT "",
`k11` datetime NULL COMMENT "",
`k7` varchar(20) NULL COMMENT "",
`k8` double NULL COMMENT "",
`k9` float NULL COMMENT ""
) ENGINE=MYSQL
COMMENT "MYSQL"
PROPERTIES (
"host" = "192.168.1.1",
"port" = "8086",
"user" = "root",
"password" = "123456",
"database" = "test",
"table" = "base"
);
```
This table have 60000 row in external table.
We do query like:
```
select * from baseall_mysql limit 10;
```
Now Doris do not push down limit clause of mysql table, so Doris fetch all row in baseall_mysql and get top 10 of the table.**it is cost unnecessary network and mem in MySQL Scan Node / ODBC Scan Node**.
In my test:
this query cost **2.1s** but push down the limit clause, **it only take 0.21s**.
So we need to support limit clause push down for ODBC Table and MySQL Table.
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[GitHub] [incubator-doris] morningman closed issue #4706: [Proposal] Support Limit Clause Push Down For ODBC Table And MySQL Table
Posted by GitBox <gi...@apache.org>.
morningman closed issue #4706:
URL: https://github.com/apache/incubator-doris/issues/4706
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