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https://issues.apache.org/jira/browse/HAWQ-1183?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15711343#comment-15711343
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Paul Guo commented on HAWQ-1183:
--------------------------------

With the previous patch, the planner and run time is as expected now. 

postgres=# explain analyze INSERT INTO ext_tbl1 SELECT * from tbl1;
QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------------------------------
Insert (cost=0.00..444.03 rows=167 width=8)
Rows out: Avg 351833.3 rows x 6 workers. Max/Last(seg5:host67/seg0:host67) 
351916/351849 rows with 89/171 ms to first row, 4074/4209 ms to end, start 
offset by 46/45 ms.
Executor memory: 1K bytes avg, 1K bytes max (seg5:host67).
-> Result (cost=0.00..431.01 rows=167 width=20)
Rows out: Avg 351833.3 rows x 6 workers. Max/Last(seg5:host67/seg0:host67) 
351916/351849 rows with 77/148 ms to first row, 292/392 ms to end, start offset 
by 46/45 ms.
-> Table Scan on tbl1 (cost=0.00..431.00 rows=167 width=8)
Rows out: Avg 351833.3 rows x 6 workers. Max/Last(seg5:host67/seg2:host67) 
351916/351855 rows with 77/152 ms to first row, 158/257 ms to end, start offset 
by 46/42
ms.
Slice statistics:
(slice0) Executor memory: 280K bytes avg x 6 workers, 280K bytes max 
(seg5:host67).
Statement statistics:
Memory used: 262144K bytes
Optimizer status: PQO version 1.684
Dispatcher statistics:
executors used(total/cached/new connection): (6/0/6); dispatcher 
time(total/connection/dispatch data): (38.288 ms/37.708 ms/0.078 ms).
dispatch data time(max/min/avg): (0.028 ms/0.004 ms/0.012 ms); consume executor 
data time(max/min/avg): (0.067 ms/0.014 ms/0.029 ms); free executor 
time(max/min/avg): (0.000 ms/0
.000 ms/0.000 ms).
Data locality statistics:
data locality ratio: 1.000; virtual segment number: 6; different host number: 
1; virtual segment number per host(avg/min/max): (6/6/6); segment 
size(avg/min/max): (7670609.333 B/
7668464 B/7672344 B); segment size with penalty(avg/min/max): (0.000 B/0 B/0 
B); continuity(avg/min/max): (1.000/1.000/1.000); DFS metadatacache: 28.855 ms; 
resource allocation: 12.
933 ms; datalocality calculation: 0.190 ms.
Total runtime: 4333.663 ms
(18 rows)


> Writable external table with Hash distribution shows slow performance
> ---------------------------------------------------------------------
>
>                 Key: HAWQ-1183
>                 URL: https://issues.apache.org/jira/browse/HAWQ-1183
>             Project: Apache HAWQ
>          Issue Type: Bug
>            Reporter: Paul Guo
>            Assignee: Paul Guo
>
> Steps:
> 1. Create tables and populate them.
> drop table tbl1;
> drop external table ext_tbl1;
> drop external table ext_tbl1_random;
> CREATE TABLE tbl1 (a int, b text) DISTRIBUTED BY (a);
> INSERT INTO tbl1 VALUES (generate_series(1,1000),'aaa');
> INSERT INTO tbl1 VALUES (generate_series(1,10000),'bbb');
> INSERT INTO tbl1 VALUES (generate_series(1,100000),'bbc');
> INSERT INTO tbl1 VALUES (generate_series(1,1000000),'bdbc');
> INSERT INTO tbl1 VALUES (generate_series(1,1000000),'bdddbc');
> CREATE WRITABLE EXTERNAL TABLE ext_tbl1
> ( LIKE tbl1 )
> LOCATION ('gpfdist://127.0.0.1/tbl1.csv')
> FORMAT 'CSV' (DELIMITER ',')
> DISTRIBUTED BY (a);
> CREATE WRITABLE EXTERNAL TABLE ext_tbl1_random
> ( LIKE tbl1 )
> LOCATION ('gpfdist://127.0.0.1/tbl1.random.csv')
> FORMAT 'CSV' (DELIMITER ',')
> DISTRIBUTED RANDOMLY;
> 2. Write the two external tables. We can find that the external table with 
> hash distribution is slow with inserting, and plan shows that it has 1 
> workers only.
> postgres=# explain analyze INSERT INTO ext_tbl1 SELECT * from tbl1;
>                              QUERY PLAN
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> --------------------------------------------------------------------
>  Insert  (cost=0.00..509.20 rows=1000 width=8)
>    Rows out:  Avg 2111000.0 rows x 1 workers.  
> Max/Last(seg0:host67/seg0:host67) 2111000/2111000 rows with 17/17 ms to first 
> row, 20145/20145 ms to end, start offset by 18/18 ms.
>    Executor memory:  1K bytes.
>    ->  Result  (cost=0.00..431.07 rows=1000 width=20)
>          Rows out:  Avg 2111000.0 rows x 1 workers.  
> Max/Last(seg0:host67/seg0:host67) 2111000/2111000 rows with 14/14 ms to first 
> row, 1919/1919 ms to end, start offset by 18/18 ms
> .
>          ->  Redistribute Motion 1:1  (slice1; segments: 1)  
> (cost=0.00..431.05 rows=1000 width=8)
>                Hash Key: tbl1.a
>                Rows out:  Avg 2111000.0 rows x 1 workers at destination.  
> Max/Last(seg0:host67/seg0:host67) 2111000/2111000 rows with 14/14 ms to first 
> row, 1273/1273 ms to end, sta
> rt offset by 18/18 ms.
>                ->  Table Scan on tbl1  (cost=0.00..431.01 rows=1000 width=8)
>                      Rows out:  Avg 2111000.0 rows x 1 workers.  
> Max/Last(seg0:host67/seg0:host67) 2111000/2111000 rows with 13/13 ms to first 
> row, 447/447 ms to end, start offset b
> y 18/18 ms.
>  Slice statistics:
>    (slice0)    Executor memory: 293K bytes (seg0:host67).
>    (slice1)    Executor memory: 303K bytes (seg0:host67).
>  Statement statistics:
>    Memory used: 262144K bytes
>  Optimizer status: PQO version 1.684
>  Dispatcher statistics:
>    executors used(total/cached/new connection): (2/0/2); dispatcher 
> time(total/connection/dispatch data): (13.138 ms/12.628 ms/0.061 ms).
>    dispatch data time(max/min/avg): (0.034 ms/0.025 ms/0.029 ms); consume 
> executor data time(max/min/avg): (0.098 ms/0.036 ms/0.067 ms); free executor 
> time(max/min/avg): (0.000 ms/0
> .000 ms/0.000 ms).
>  Data locality statistics:
>    data locality ratio: 1.000; virtual segment number: 1; different host 
> number: 1; virtual segment number per host(avg/min/max): (1/1/1); segment 
> size(avg/min/max): (46023656.000 B
> /46023656 B/46023656 B); segment size with penalty(avg/min/max): 
> (46023656.000 B/46023656 B/46023656 B); continuity(avg/min/max): 
> (1.000/1.000/1.000); DFS metadatacache: 27.930 ms;
> resource allocation: 11.879 ms; datalocality calculation: 0.207 ms.
>  Total runtime: 20356.994 ms
> (22 rows)
> postgres=#
> postgres=# explain analyze INSERT INTO ext_tbl1_random SELECT * from tbl1;
>                 QUERY PLAN
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> ------------------------------------------
>  Insert  (cost=0.00..444.03 rows=167 width=8)
>    Rows out:  Avg 351833.3 rows x 6 workers.  
> Max/Last(seg2:host67/seg5:host67) 351984/351854 rows with 61/51 ms to first 
> row, 4731/4767 ms to end, start offset by 67/75 ms.
>    Executor memory:  1K bytes avg, 1K bytes max (seg5:host67).
>    ->  Result  (cost=0.00..431.01 rows=167 width=20)
>          Rows out:  Avg 351833.3 rows x 6 workers.  
> Max/Last(seg2:host67/seg1:host67) 351984/351734 rows with 35/29 ms to first 
> row, 616/705 ms to end, start offset by 67/77 ms.
>          ->  Redistribute Motion 6:6  (slice1; segments: 6)  
> (cost=0.00..431.01 rows=167 width=8)
>                Rows out:  Avg 351833.3 rows x 6 workers at destination.  
> Max/Last(seg2:host67/seg1:host67) 351984/351734 rows with 35/29 ms to first 
> row, 439/485 ms to end, start of
> fset by 67/77 ms.
>                ->  Table Scan on tbl1  (cost=0.00..431.00 rows=167 width=8)
>                      Rows out:  Avg 351833.3 rows x 6 workers.  
> Max/Last(seg5:host67/seg4:host67) 351916/351801 rows with 45/34 ms to first 
> row, 134/146 ms to end, start offset by 7
> 4/82 ms.
>  Slice statistics:
>    (slice0)    Executor memory: 293K bytes avg x 6 workers, 293K bytes max 
> (seg5:host67).
>    (slice1)    Executor memory: 384K bytes avg x 6 workers, 384K bytes max 
> (seg5:host67).
>  Statement statistics:
>    Memory used: 262144K bytes
>  Optimizer status: PQO version 1.684
>  Dispatcher statistics:
>    executors used(total/cached/new connection): (12/2/10); dispatcher 
> time(total/connection/dispatch data): (68.122 ms/1480579527424.677 ms/3.747 
> ms).
>    dispatch data time(max/min/avg): (0.203 ms/0.004 ms/0.029 ms); consume 
> executor data time(max/min/avg): (0.052 ms/0.007 ms/0.017 ms); free executor 
> time(max/min/avg): (0.000 ms/0
> .000 ms/0.000 ms).
>  Data locality statistics:
>    data locality ratio: 1.000; virtual segment number: 6; different host 
> number: 1; virtual segment number per host(avg/min/max): (6/6/6); segment 
> size(avg/min/max): (7670609.333 B/
> 7668464 B/7672344 B); segment size with penalty(avg/min/max): (0.000 B/0 B/0 
> B); continuity(avg/min/max): (1.000/1.000/1.000); DFS metadatacache: 0.104 
> ms; resource allocation: 0.67
> 1 ms; datalocality calculation: 0.109 ms.
>  Total runtime: 4884.780 ms
> (21 rows)



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