Executing an SQL statement in parallel (using either intrapartition or interpartition parallelism) requires some special access plan operations.
Process Using n Subagents
Distribute Subsection #n
Directed by Hash
| #Columns = n
| Partition Map ID = n, Nodegroup = ngname, #Nodes = n
Directed by Node Number
Directed by Partition Number
| Partition Map ID = n, Nodegroup = ngname, #Nodes = n
Directed by Position
Directed to Single Node
| Node Number = n
Directed to Application Coordinator Node
Directed to Local Coordinator Node
Broadcast to Node List
| Nodes = n1, n2, n3, ...
Directed to Any Node
Insert Into Synchronous Table Queue ID = qn
Insert Into Asynchronous Table Queue ID = qn
Insert Into Synchronous Local Table Queue ID = qn
Insert Into Asynchronous Local Table Queue ID = qn
Broadcast to Coordinator Node
Each
row is sent to every database partition on which the given subsection
is running: Broadcast to All Nodes of Subsection n
Each
row is sent to a database partition that is based on the values in
the row: Hash to Specific Node
Each row is
sent to a database partition that is determined while the statement
is executing: Send to Specific Node
Each
row is sent to a randomly determined database partition: Send to Random Node
Rows Can Overflow to Temporary Table
Insert Into Synchronous Table Queue Completion ID = qn
Insert Into Asynchronous Table Queue Completion ID = qn
Insert Into Synchronous Local Table Queue Completion ID = qn
Insert Into Asynchronous Local Table Queue Completion ID = qn
Access Table Queue ID = qn
Access Local Table Queue ID = qn
These statements are
always followed by the number of columns being retrieved. #Columns = n
Output Sorted
Output Sorted and Unique
These statements are followed
by the number of keys being used for the sort operation. #Key Columns = n
For
each column in the sort key, one of the following statements is displayed: Key n: (Ascending)
Key n: (Descending)
Residual Predicate(s)
| #Predicates = n
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