Node name: TQ
Represents: A table queue that is used to pass table data from one database agent to another when there are multiple database agents processing a query. Multiple database agents are used to process a query when parallelism is involved.
Based on the origin type, TQ nodes are of two types:
The XTQ node is a table queue that constructs a XML sequence from XML documents stored on database partitions.
Xquery let $all_orders := db2-fn:xmlcolumn('US_ORDERS.DETAILS')
where sum($all_orders//product/qty) > 100
return $all_orders
For
the XQuery statement, the db2exfmt command produces
the following access plan output that contains an XTQ node. In the
plan output, references to all the XML documents stored in US_ORDERS.DETAILS
column are routed (DTQ: Directed TQ) to the coordinator partition
and aggregated into a global sequence, later each item in the global
sequence is routed back to its original partition for navigation and
the results are aggregated together into a new output global sequence
(XTQ: XSCAN related TQ). Rows
RETURN
( 1)
Cost
I/O
|
1
NLJOIN
( 2)
98.171
8
/-+-\
1 2000
FILTER XTQ
( 3) ( 7)
37.4289 60.7421
1 7
| |
1 0.5
GRPBY XSCAN
( 4) ( 8)
37.3755 57.2
1 7
|
360
DTQ
( 5)
33.7655
1
|
180
TBSCAN
( 6)
22.051
1
|
180
TABLE: USER1
US_ORDERS