Neoview Query Guide (R2.2)

can execute in the master executor or ESP processes, and groupbys can execute in the master
executor, ESP, or DAM processes.
Certain scan operators always execute in the same process. For example, the scan operators,
including FILE_SCAN and FILE_SCAN_UNIQUE, always execute in the DAM process. The
ROOT operator always executes in the master executor process.
VQP plans only show the operators that represent the process boundaries and indicate the number
of processes used or accessed. They do not show each individual process involved in executing
the query.
Although the VQP plan appears to show only four processes, many other processes are used to
execute the query plan. The plan shows a ROOT process, an ESP process, and two DAM processes.
The notation 512->1 indicates that 512 ESPs are used to perform the nested join operation. The
first number, 512, refers to the bottom partitioning information (in this case, the nested join
operation across 512 DAM processes), and 1 refers to the root, or master executor process where
the information is rolled up.
The SPLIT_TOP Operator
Although not considered a process boundary operator, the SPLIT_TOP operator indicates that
the process needs to access more than one partition of a table through the PARTITION_ACCESS
operator. The access might be parallel. Additionally, the SPLIT_TOP operator can be present in
the master executor and ESP processes. It facilitates DAM parallelism and consolidates data. In
this figure, the SPLIT_TOP operator accesses 128 DAM processes and feeds the results to the
master executor process.
The query plans shown next demonstrate the significance of access through the
PARTITION_ACCESS operator alone and in combination with the SPLIT_TOP operator. The
first plan shows a matching partitions hybrid hash join with 512 ESPs that are used to do the join
between pairs of partitions from the tables. These joins are completely independent of one another
because each ESP will access one partition directly from both tables. The plan lacks a SPLIT_TOP
operator so the ESP will access the partition directly in a one-to-one correspondence. When only
one partition needs to be accessed, only the PARTITION_ACCESS operator is required.
Understanding the Query Plan in VQP 29