jiaqizho commented on issue #659:
URL: https://github.com/apache/cloudberry/issues/659#issuecomment-2482268565
my test case is
```
create table t1(v1 int, v2 int, v3 int);
insert into t1 values(generate_series(0, 100000), generate_series(100000,
200000), generate_series(200000, 300000));
insert into t1 select * from t1; -- do n times
```
and the ORCA memo is:
```
postgres=# explain analyze WITH UniqueIDs AS (
SELECT DISTINCT v2
FROM t1
)
SELECT COUNT(*)
FROM UniqueIDs;
LOG: statement: explain analyze WITH UniqueIDs AS (
SELECT DISTINCT v2
FROM t1
)
SELECT COUNT(*)
FROM UniqueIDs;
LOG: 2024-11-18 14:15:17:640135 CST,THD000,TRACE,"MEMO after optimization
(stage 0):
",
2024-11-18 14:15:17:642637 CST,THD000,TRACE,"
Group 19 ():
0: CScalarConst (1) [ ]
Group 18 ():
0: CScalarProjectList [ 17 ]
Group 17 ():
0: CScalarProjectElement "count" (22) [ 16 ]
Group 16 ():
0: CScalarAggFunc (count , Distinct: false , Aggregate Stage: Global) [ 15
1 1 1 ]
Group 15 ():
0: CScalarValuesList [ 14 ]
Group 14 ():
0: CScalarIdent "ColRef_0023" (23) [ ]
Group 13 (#GExprs: 3):
0: CLogicalGbAgg( Local ) Grp Cols: [][Local], Minimal Grp Cols: [],
Generates Duplicates :[ 1 ] [ 0 12 ]
1: CPhysicalScalarAgg( Local, multi-stage ) Grp Cols: [], Minimal Grp
Cols:[], Generates Duplicates :[ 1 ] [ 0 12 ]
Cost Ctxts:
main ctxt (stage 0)1.0, child ctxts:[1], rows:1.000000 (group), cost:
1093.902454
main ctxt (stage 0)1.1, child ctxts:[2], rows:1.000000 (group), cost:
1094.007472
2: CPhysicalMotionGather(master) [ 13 ]
Cost Ctxts:
main ctxt (stage 0)0.0, child ctxts:[1], rows:1.000000 (group), cost:
1093.902484
Grp OptCtxts:
0 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [SINGLETON (master) match: satisfy], req rewind: [], req rewind:
[NONE NO-MOTION match: satisfy], req partition propagation: [<empty> match:
satisfy ]) => Best Expr:2
1 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [ANY EOperatorId: 129 match: satisfy], req rewind: [], req
rewind: [NONE NO-MOTION match: satisfy], req partition propagation: [<empty>
match: satisfy ]) => Best Expr:1
Group 12 ():
0: CScalarProjectList [ 11 ]
Group 11 ():
0: CScalarProjectElement "ColRef_0023" (23) [ 10 ]
Group 10 ():
0: CScalarAggFunc (count , Distinct: false , Aggregate Stage: Local) [ 1 1
1 1 ]
Group 9 (#GExprs: 5):
0: CLogicalGbAgg( Local ) Grp Cols: ["v2" (11)][Local], Minimal Grp Cols:
["v2" (11)], Generates Duplicates :[ 1 ] [ 7 8 ]
1: CPhysicalStreamAgg( Local, multi-stage ) Grp Cols: ["v2" (11)], Minimal
Grp Cols:["v2" (11)], Generates Duplicates :[ 1 ] [ 7 8 ]
Cost Ctxts:
main ctxt (stage 0)1.0, child ctxts:[4], rows:100656.000000 (group),
cost: 2719.140939
main ctxt (stage 0)1.1, child ctxts:[3], rows:100656.000000 (group),
cost: 2772.560140
2: CPhysicalHashAgg( Local, multi-stage ) Grp Cols: ["v2" (11)], Minimal
Grp Cols:["v2" (11)], Generates Duplicates :[ 1 ] (High) [ 7 8 ]
Cost Ctxts:
main ctxt (stage 0)1.0, child ctxts:[1], rows:100656.000000 (group),
cost: 1089.433563
main ctxt (stage 0)1.1, child ctxts:[2], rows:100656.000000 (group),
cost: 1142.852763
3: CPhysicalMotionHashDistribute HASHED: [ CScalarIdent "v2" (11), nulls
colocated ], opfamilies: (1977,1.0), [ 9 ]
Cost Ctxts:
main ctxt (stage 0)0.0, child ctxts:[1], rows:100656.000000 (group),
cost: 1089.853634
4: CPhysicalSort ( (97,1.0), "v2" (11), NULLsLast ) [ 9 ]
Cost Ctxts:
main ctxt (stage 0)2.0, child ctxts:[0], rows:100656.000000 (group),
cost: 1101.293981
Grp OptCtxts:
0 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [HASHED: [ CScalarIdent "v2" (11), nulls colocated ], opfamilies:
(1977,1.0), match: satisfy], req rewind: [], req rewind: [NONE NO-MOTION match:
satisfy], req partition propagation: [<empty> match: satisfy ]) => Best Expr:3
1 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [ANY EOperatorId: 131 match: satisfy], req rewind: [], req
rewind: [NONE NO-MOTION match: satisfy], req partition propagation: [<empty>
match: satisfy ]) => Best Expr:2
2 (stage 0): (req CTEs: [0:p(opt) ], req order: [( (97,1.0), "v2" (11),
NULLsLast ) match: satisfy ], req dist: [HASHED: [ CScalarIdent "v2" (11),
nulls colocated ], opfamilies: (1977,1.0), match: satisfy], req rewind: [], req
rewind: [NONE NO-MOTION match: satisfy], req partition propagation: [<empty>
match: satisfy ]) => Best Expr:4
Group 8 ():
0: CScalarProjectList [ ]
Group 7 (#GExprs: 5):
0: CLogicalGet "t1" ("t1"), Columns: ["v1" (12), "v2" (11), "v3" (13),
"ctid" (14), "xmin" (15), "cmin" (16), "xmax" (17), "cmax" (18), "tableoid"
(19), "gp_segment_id" (20), "gp_foreign_server" (21)] Key sets: {[3,9]} [ ]
1: CPhysicalTableScan "t1" ("t1") [ ]
Cost Ctxts:
main ctxt (stage 0)1.0, child ctxts:[], rows:12800128.000000 (group),
cost: 538.947746
2: CPhysicalMotionHashDistribute HASHED: [ CScalarIdent "v2" (11), nulls
colocated ], opfamilies: (1977,1.0), [ 7 ]
Cost Ctxts:
main ctxt (stage 0)0.0, child ctxts:[1], rows:12800128.000000 (group),
cost: 624.111264
3: CPhysicalMotionRandom [ 7 ]
Cost Ctxts:
main ctxt (stage 0)2.0, child ctxts:[1], rows:12800128.000000 (group),
cost: 624.111264
4: CPhysicalSort ( (97,1.0), "v2" (11), NULLsLast ) [ 7 ]
Cost Ctxts:
main ctxt (stage 0)4.0, child ctxts:[1], rows:12800128.000000 (group),
cost: 2701.998811
main ctxt (stage 0)5.0, child ctxts:[0], rows:12800128.000000 (group),
cost: 2755.418012
main ctxt (stage 0)3.0, child ctxts:[2], rows:12800128.000000 (group),
cost: 2755.418012
Grp OptCtxts:
0 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [HASHED: [ CScalarIdent "v2" (11), nulls colocated ], opfamilies:
(1977,1.0), match: satisfy], req rewind: [], req rewind: [NONE NO-MOTION match:
satisfy], req partition propagation: [<empty> match: satisfy ]) => Best Expr:2
1 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [ANY EOperatorId: 131 match: satisfy], req rewind: [], req
rewind: [NONE NO-MOTION match: satisfy], req partition propagation: [<empty>
match: satisfy ]) => Best Expr:1
2 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [RANDOM match: satisfy], req rewind: [], req rewind: [NONE
NO-MOTION match: satisfy], req partition propagation: [<empty> match: satisfy
]) => Best Expr:3
3 (stage 0): (req CTEs: [0:p(opt) ], req order: [( (97,1.0), "v2" (11),
NULLsLast ) match: satisfy ], req dist: [RANDOM match: satisfy], req rewind:
[], req rewind: [NONE NO-MOTION match: satisfy], req partition propagation:
[<empty> match: satisfy ]) => Best Expr:4
4 (stage 0): (req CTEs: [0:p(opt) ], req order: [( (97,1.0), "v2" (11),
NULLsLast ) match: satisfy ], req dist: [ANY EOperatorId: 136 match:
satisfy], req rewind: [], req rewind: [NONE NO-MOTION match: satisfy], req
partition propagation: [<empty> match: satisfy ]) => Best Expr:4
5 (stage 0): (req CTEs: [0:p(opt) ], req order: [( (97,1.0), "v2" (11),
NULLsLast ) match: satisfy ], req dist: [HASHED: [ CScalarIdent "v2" (11),
nulls colocated ], opfamilies: (1977,1.0), match: satisfy], req rewind: [], req
rewind: [NONE NO-MOTION match: satisfy], req partition propagation: [<empty>
match: satisfy ]) => Best Expr:4
ROOT
Group 6 (#GExprs: 3):
0: CLogicalCTEAnchor (0) [ 5 ]
1: CLogicalSelect [ 5 19 ]
2: CPhysicalFilter [ 5 19 ]
Cost Ctxts:
main ctxt (stage 0)0.1, child ctxts:[0], rows:1.000000 (group), cost:
1093.902485 -- group 5 outer
Grp OptCtxts:
0 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [SINGLETON (master) match: satisfy], req rewind: [], req rewind:
[NONE NO-MOTION match: satisfy], req partition propagation: [<empty> match:
satisfy ]) => Best Expr:2
Group 5 (#GExprs: 4):
0: CLogicalGbAgg( Global ) Grp Cols: [][Global], Minimal Grp Cols: [],
Generates Duplicates :[ 0 ] [ 0 4 ]
1: CLogicalGbAgg( Global ) Grp Cols: [][Global], Minimal Grp Cols: [],
Generates Duplicates :[ 1 ] [ 13 18 ]
2: CPhysicalScalarAgg( Global, multi-stage ) Grp Cols: [], Minimal Grp
Cols:[], Generates Duplicates :[ 1 ] [ 13 18 ]
Cost Ctxts:
main ctxt (stage 0)0.1, child ctxts:[0], rows:1.000000 (group), cost:
1093.902485
3: CPhysicalScalarAgg( Global ) Grp Cols: [], Minimal Grp Cols:[],
Generates Duplicates :[ 0 ] [ 0 4 ]
Cost Ctxts:
main ctxt (stage 0)0.1, child ctxts:[0], rows:1.000000 (group), cost:
1094.277565
Grp OptCtxts:
0 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [ANY EOperatorId: 101 match: satisfy], req rewind: [], req
rewind: [NONE NO-MOTION match: satisfy], req partition propagation: [<empty>
match: satisfy ]) => Best Expr:2
Group 4 ():
0: CScalarProjectList [ 3 ]
Group 3 ():
0: CScalarProjectElement "count" (22) [ 2 ]
Group 2 ():
0: CScalarAggFunc (count , Distinct: false , Aggregate Stage: Global) [ 1
1 1 1 ]
Group 1 ():
0: CScalarValuesList [ ]
Group 0 (#GExprs: 10):
0: CLogicalCTEConsumer (0), Columns: ["v2" (11)] [ ]
1: CLogicalGbAgg( Global ) Grp Cols: ["v2" (11)][Global], Minimal Grp
Cols: ["v2" (11)], Generates Duplicates :[ 0 ] [ 7 8 ]
2: CLogicalGbAgg( Global ) Grp Cols: ["v2" (11)][Global], Minimal Grp
Cols: ["v2" (11)], Generates Duplicates :[ 1 ] [ 9 8 ]
3: CPhysicalStreamAgg( Global, multi-stage ) Grp Cols: ["v2" (11)],
Minimal Grp Cols:["v2" (11)], Generates Duplicates :[ 1 ] [ 9 8 ]
Cost Ctxts:
main ctxt (stage 0)1.1, child ctxts:[2], rows:100656.000000 (group),
cost: 1101.447012
4: CPhysicalHashAgg( Global, multi-stage ) Grp Cols: ["v2" (11)], Minimal
Grp Cols:["v2" (11)], Generates Duplicates :[ 1 ] (High) [ 9 8 ]
Cost Ctxts:
main ctxt (stage 0)1.1, child ctxts:[0], rows:100656.000000 (group),
cost: 1093.902454
5: CPhysicalStreamAgg( Global ) Grp Cols: ["v2" (11)], Minimal Grp
Cols:["v2" (11)], Generates Duplicates :[ 0 ] [ 7 8 ]
Cost Ctxts:
main ctxt (stage 0)1.1, child ctxts:[5], rows:100656.000000 (group),
cost: 2772.503672
6: CPhysicalHashAgg( Global ) Grp Cols: ["v2" (11)], Minimal Grp
Cols:["v2" (11)], Generates Duplicates :[ 0 ] (High) [ 7 8 ]
Cost Ctxts:
main ctxt (stage 0)1.1, child ctxts:[0], rows:100656.000000 (group),
cost: 1136.613079
7: CPhysicalCTEConsumer (0), Columns: ["v2" (11)] [ ]
Cost Ctxts:
8: CPhysicalMotionGather(master) [ 0 ]
Cost Ctxts:
main ctxt (stage 0)0.0, child ctxts:[1], rows:100656.000000 (group),
cost: 1094.277565
9: CPhysicalMotionRandom [ 0 ]
Cost Ctxts:
main ctxt (stage 0)2.0, child ctxts:[1], rows:100656.000000 (group),
cost: 1094.007472
Grp OptCtxts:
0 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [SINGLETON (master) match: satisfy], req rewind: [], req rewind:
[NONE NO-MOTION match: satisfy], req partition propagation: [<empty> match:
satisfy ]) => Best Expr:8
1 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [ANY EOperatorId: 129 match: satisfy], req rewind: [], req
rewind: [NONE NO-MOTION match: satisfy], req partition propagation: [<empty>
match: satisfy ]) => Best Expr:4
2 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy
], req dist: [RANDOM match: satisfy], req rewind: [], req rewind: [NONE
NO-MOTION match: satisfy], req partition propagation: [<empty> match: satisfy
]) => Best Expr:9
",
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Finalize Aggregate (cost=0.00..1093.90 rows=1 width=8) (actual
time=3749.832..3749.845 rows=1 loops=1)
-> Gather Motion 3:1 (slice1; segments: 3) (cost=0.00..1093.90 rows=1
width=8) (actual time=3744.143..3749.815 rows=3 loops=1)
-> Partial Aggregate (cost=0.00..1093.90 rows=1 width=8) (actual
time=3748.275..3748.276 rows=1 loops=1)
-> HashAggregate (cost=0.00..1093.90 rows=33552 width=1)
(actual time=3728.835..3738.960 rows=33501 loops=1)
Group Key: v2
-> Redistribute Motion 3:3 (slice2; segments: 3)
(cost=0.00..1089.85 rows=33552 width=4) (actual time=3277.019..3706.719
rows=33501 loops=1)
Hash Key: v2
-> Streaming HashAggregate (cost=0.00..1089.43
rows=33552 width=4) (actual time=3694.054..3706.532 rows=33462 loops=1)
Group Key: v2
-> Seq Scan on t1 (cost=0.00..538.95
rows=4266710 width=4) (actual time=0.175..1717.717 rows=4283136 loops=1)
Planning Time: 60.859 ms
(slice0) Executor memory: 3139K bytes.
(slice1) Executor memory: 2617K bytes avg x 3x(0) workers, 2623K bytes
max (seg2). Work_mem: 3601K bytes max.
(slice2) Executor memory: 2615K bytes avg x 3x(0) workers, 2619K bytes
max (seg0). Work_mem: 3601K bytes max.
Memory used: 128000kB
Optimizer: Pivotal Optimizer (GPORCA)
Execution Time: 3762.223 ms
(17 rows)
```
then the lowest cost path is:
```
ROOT -> 5 9 * [0] (CPhysicalFilter)
-> 5 * 0 (CPhysicalScalarAgg)
-> 13 * 0 (CPhysicalMotionGather)
-> 0 * 1 (CPhysicalHashAgg)
-> 9 * 0 (CPhysicalMotionHashDistribute)
-> 9 * 1 (CPhysicalHashAgg)
-> 7 * 1 (CPhysicalTableScan)
```
let us see the group 7(only one path to do the seq scan):
```
Group 7 (#GExprs: 5):
...
1: CPhysicalTableScan "t1" ("t1") [ ]
Cost Ctxts:
main ctxt (stage 0)1.0, child ctxts:[], rows:12800128.000000 (group),
cost: 538.947746
...
1 (stage 0): (req CTEs: [0:p(opt) ], req order: [<empty> match: satisfy ],
req dist: [ANY EOperatorId: 131 match: satisfy], req rewind: [], req rewind:
[NONE NO-MOTION match: satisfy], req partition propagation: [<empty> match:
satisfy ]) => Best Expr:1
```
then below path can add `group 7, expr 1` as its child:
- group 7,expr 2 - CPhysicalMotionHashDistribute
- group 7,expr 3 - CPhysicalMotionRandom
- group 7,expr 3 - Sort(high cost)
- group 9,expr 1 - CPhysicalHashAgg
The parent path of path abc `group 9,expr 1` the same as `group 7, expr 1`,
and only `CPhysicalMotionHashDistribute/CPhysicalMotionRandom/Sort` path
exists.
So i guess we need add a path in the ORCA...
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