Enable parallel SELECT for "INSERT INTO ... SELECT ...".

Parallel SELECT can't be utilized for INSERT in the following cases:
- INSERT statement uses the ON CONFLICT DO UPDATE clause
- Target table has a parallel-unsafe: trigger, index expression or
  predicate, column default expression or check constraint
- Target table has a parallel-unsafe domain constraint on any column
- Target table is a partitioned table with a parallel-unsafe partition key
  expression or support function

The planner is updated to perform additional parallel-safety checks for
the cases listed above, for determining whether it is safe to run INSERT
in parallel-mode with an underlying parallel SELECT. The planner will
consider using parallel SELECT for "INSERT INTO ... SELECT ...", provided
nothing unsafe is found from the additional parallel-safety checks, or
from the existing parallel-safety checks for SELECT.

While checking parallel-safety, we need to check it for all the partitions
on the table which can be costly especially when we decide not to use a
parallel plan. So, in a separate patch, we will introduce a GUC and or a
reloption to enable/disable parallelism for Insert statements.

Prior to entering parallel-mode for the execution of INSERT with parallel
SELECT, a TransactionId is acquired and assigned to the current
transaction state. This is necessary to prevent the INSERT from attempting
to assign the TransactionId whilst in parallel-mode, which is not allowed.
This approach has a disadvantage in that if the underlying SELECT does not
return any rows, then the TransactionId is not used, however that
shouldn't happen in practice in many cases.

Author: Greg Nancarrow, Amit Langote, Amit Kapila
Reviewed-by: Amit Langote, Hou Zhijie, Takayuki Tsunakawa, Antonin Houska, Bharath Rupireddy, Dilip Kumar, Vignesh C, Zhihong Yu, Amit Kapila
Tested-by: Tang, Haiying
Discussion: https://postgr.es/m/CAJcOf-cXnB5cnMKqWEp2E2z7Mvcd04iLVmV=qpFJrR3AcrTS3g@mail.gmail.com
Discussion: https://postgr.es/m/CAJcOf-fAdj=nDKMsRhQzndm-O13NY4dL6xGcEvdX5Xvbbi0V7g@mail.gmail.com

1 files changed, 2 insertions, 1 deletions

diff --git a/src/include/optimizer/clauses.h b/src/include/optimizer/clauses.h
index 0673887a85..8d85b02514 100644
--- a/src/include/optimizer/clauses.h
+++ b/src/include/optimizer/clauses.h
@@ -32,7 +32,7 @@ extern double expression_returns_set_rows(PlannerInfo *root, Node *clause);
 
 extern bool contain_subplans(Node *clause);
 
-extern char max_parallel_hazard(Query *parse);
+extern char max_parallel_hazard(Query *parse, PlannerGlobal *glob);
 extern bool is_parallel_safe(PlannerInfo *root, Node *node);
 extern bool contain_nonstrict_functions(Node *clause);
 extern bool contain_exec_param(Node *clause, List *param_ids);
@@ -52,5 +52,6 @@ extern void CommuteOpExpr(OpExpr *clause);
 
 extern Query *inline_set_returning_function(PlannerInfo *root,
 											RangeTblEntry *rte);
+extern bool is_parallel_allowed_for_modify(Query *parse);
 
 #endif							/* CLAUSES_H */