mirror of
https://github.com/postgres/postgres.git
synced 2025-08-25 20:23:07 +03:00
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
This commit is contained in:
@@ -1014,6 +1014,32 @@ IsInParallelMode(void)
|
||||
return CurrentTransactionState->parallelModeLevel != 0;
|
||||
}
|
||||
|
||||
/*
|
||||
* PrepareParallelModePlanExec
|
||||
*
|
||||
* Prepare for entering parallel mode plan execution, based on command-type.
|
||||
*/
|
||||
void
|
||||
PrepareParallelModePlanExec(CmdType commandType)
|
||||
{
|
||||
if (IsModifySupportedInParallelMode(commandType))
|
||||
{
|
||||
Assert(!IsInParallelMode());
|
||||
|
||||
/*
|
||||
* Prepare for entering parallel mode by assigning a TransactionId.
|
||||
* Failure to do this now would result in heap_insert() subsequently
|
||||
* attempting to assign a 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.
|
||||
*/
|
||||
(void) GetCurrentTransactionId();
|
||||
}
|
||||
}
|
||||
|
||||
/*
|
||||
* CommandCounterIncrement
|
||||
*/
|
||||
|
Reference in New Issue
Block a user