liutang123 opened a new issue #4481:
URL: https://github.com/apache/incubator-doris/issues/4481
issue Reason
--
Now, Doris will create two fragments for aggretion.
Sometime, **Exchange for aggregation is unnecessary.**
Think about follow cases:
1. aggregate an unpartitioned table.
a. create table SQL:
```
CREATE TABLE `llj_test_1` (
`dt` int(11) NOT NULL COMMENT "",
`dis_key` varchar(20) NOT NULL COMMENT ""
) ENGINE=OLAP
DUPLICATE KEY(`dt`, `dis_key`)
COMMENT "OLAP"
DISTRIBUTED BY HASH(`dt`, `dis_key`) BUCKETS 3
PROPERTIES (
"replication_num" = "3",
"in_memory" = "false",
"storage_format" = "DEFAULT"
);
```
b. query SQL:`select dt, dis_key,count(1) from llj_test_1 group by dt,
dis_key;`
2. aggregate a partitioned table:
a. create table SQL:
```
CREATE TABLE `llj_test` (
`dt` int(11) NOT NULL COMMENT "",
`dis_key` varchar(20) NOT NULL COMMENT ""
) ENGINE=OLAP
DUPLICATE KEY(`dt`, `dis_key`)
COMMENT "OLAP"
PARTITION BY RANGE(`dt`)
(PARTITION p20180822 VALUES [("19000101"), ("20181021")),
PARTITION p20181207 VALUES [("20181021"), ("20181022")))
DISTRIBUTED BY HASH(`dt`, `dis_key`) BUCKETS 3
PROPERTIES (
"replication_num" = "1",
"in_memory" = "false",
"storage_format" = "DEFAULT"
);
```
b. query SQL:`select dt, dis_key,count(1) from llj_test group by dt,
dis_key;`
Suggestion
--
In `DistributedPlanner`, do not add the unnecessary `Exchange`s.
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