I hava below two statement sql:

0. not in subquery

select a.schemaname, pg_size_pretty(pg_total_relation_size(a.schemaname||'.'||a.tablename)) from pg_tables a where a.tablename not in (select b.tablename from t b);

1. in subquery

select a.schemaname, pg_size_pretty(pg_total_relation_size(a.schemaname||'.'||a.tablename)) from pg_tables a where a.tablename in (select b.tablename from t b);



The [0. not in subquery] can't work well, it's occur error:

ERROR: query plan with multiple segworker groups is not supported (cdbdisp.c:500)

HINT: likely caused by a function that reads or modifies data in a distributed table

CONTEXT: SQL statement "select sum(pg_total_relation_size('information_schema.sql_languages'))::int8 from gp_dist_random('gp_id');"



The [1. in subquery] work well.



Detailed below test:

gtlions=# select version();

version

------------------------------------------------------------------------------------------------------------------------------------------------------

PostgreSQL 8.2.15 (Greenplum Database 4.2.7.3 build 1) on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC) 4.4.2 compiled on May 7 2014 14:31:08

(1 row)

gtlions=# select a.schemaname, pg_size_pretty(pg_total_relation_size(a.schemaname||'.'||a.tablename)) from pg_tables a where a.tablename not in (select b.tablename from t b);

ERROR: query plan with multiple segworker groups is not supported (cdbdisp.c:500)

HINT: likely caused by a function that reads or modifies data in a distributed table

CONTEXT: SQL statement "select sum(pg_total_relation_size('information_schema.sql_languages'))::int8 from gp_dist_random('gp_id');"

gtlions=# explain select a.schemaname, pg_size_pretty(pg_total_relation_size(a.schemaname||'.'||a.tablename)) from pg_tables a where a.tablename not in (select b.tablename from t b);

QUERY PLAN

-----------------------------------------------------------------------------------------------

Hash Left Anti Semi Join (cost=568.98..235912.69 rows=676396 width=128)

Hash Cond: c.relname = "NotIn_SUBQUERY".tablename::name

-> Hash Left Join (cost=395.97..223194.68 rows=676419 width=128)

Hash Cond: c.relnamespace = n.oid

-> Hash Left Join (cost=2.62..112777.67 rows=676419 width=68)

Hash Cond: c.reltablespace = t.oid

-> Seq Scan on pg_class c (cost=0.00..2751.39 rows=676419 width=72)

Filter: relkind = 'r'::"char" AND relname IS NOT NULL

-> Hash (cost=1.02..1.02 rows=2 width=4)

-> Seq Scan on pg_tablespace t (cost=0.00..1.02 rows=128 width=4)

-> Hash (cost=365.35..365.35 rows=35 width=68)

-> Seq Scan on pg_namespace n (cost=0.00..365.35 rows=2240 width=68)

-> Hash (cost=106.61..106.61 rows=83 width=274)

-> Gather Motion 64:1 (slice1; segments: 64) (cost=0.00..106.61 rows=83 width=274)

-> Subquery Scan "NotIn_SUBQUERY" (cost=0.00..52.66 rows=2 width=274)

-> Seq Scan on t b (cost=0.00..51.83 rows=2 width=24)

(16 rows)

gtlions=# select a.schemaname, pg_size_pretty(pg_total_relation_size(a.schemaname||'.'||a.tablename)) from pg_tables a where a.tablename in (select b.tablename from t b);

schemaname | size-1

-------------+---------

public | 32 kB

public | 32 kB

......

......

public | 96 kB

gtlions=# explain select a.schemaname, pg_size_pretty(pg_total_relation_size(a.schemaname||'.'||a.tablename)) from pg_tables a where a.tablename in (select b.tablename from t b);

QUERY PLAN

---------------------------------------------------------------------------------------------------------------------------------

Gather Motion 64:1 (slice7; segments: 64) (cost=445.41..10096.03 rows=1 width=128)

-> Hash Left Join (cost=445.41..10096.03 rows=1 width=128)

Hash Cond: c.reltablespace = t.oid

-> Redistribute Motion 64:64 (slice5; segments: 64) (cost=443.06..10092.81 rows=1 width=132)

Hash Key: c.reltablespace

-> Hash Left Join (cost=443.06..10092.22 rows=1 width=132)

Hash Cond: c.relnamespace = n.oid

-> Redistribute Motion 64:64 (slice3; segments: 64) (cost=54.53..9703.24 rows=1 width=72)

Hash Key: c.relnamespace

-> Hash EXISTS Join (cost=54.53..9702.65 rows=1 width=72)

Hash Cond: c.relname = b.tablename::name

-> Redistribute Motion 1:64 (slice1) (cost=0.00..9621.26 rows=10570 width=72)

Hash Key: c.relname

-> Seq Scan on pg_class c (cost=0.00..2751.39 rows=676419 width=72)

Filter: relkind = 'r'::"char"

-> Hash (cost=53.49..53.49 rows=2 width=24)

-> Redistribute Motion 64:64 (slice2; segments: 64) (cost=0.00..53.49 rows=2 width=24)

Hash Key: b.tablename::name

-> Seq Scan on t b (cost=0.00..51.83 rows=2 width=24)

-> Hash (cost=388.10..388.10 rows=1 width=68)

-> Redistribute Motion 1:64 (slice4) (cost=0.00..388.10 rows=35 width=68)

Hash Key: n.oid

-> Seq Scan on pg_namespace n (cost=0.00..365.35 rows=2240 width=68)

-> Hash (cost=2.32..2.32 rows=1 width=4)

-> Redistribute Motion 1:64 (slice6) (cost=0.00..2.32 rows=2 width=4)

Hash Key: t.oid

-> Seq Scan on pg_tablespace t (cost=0.00..1.02 rows=128 width=4)

(27 rows) 

该问题应该是个Bug,等一下TSE鉴于Fix或不Fix而只是等待，直到下一个版本升级.

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