For the TBSCAN operator, the following input
arguments are shown:
- Scan source
- The source over which the scan occurs (either base tables or input
plans).
- Scanned table
- The quantifier of the table to be scanned.
- Columns retrieved
- The set of columns to be accessed.
- Sargable predicates
- The set of predicates to be applied as
sargable (that is, that can be resolved by the database manager by simple
comparisons rather than by subqueries).
- Scan direction
- The direction of the scan (either forward or reverse).
- Residual predicates
- The set of additional predicates to be applied as residuals.
- Prefetch
- A flag indicating the type of prefetching. Possible values
are:
- Sequential detection is enabled
- A positive number indicating the number of row identifiers (RIDs) for list
prefetch
- Prefetching is not enabled.
- Maximum pages
- The maximum number of pages of the table expected to be read from
disk. Possible values are:
- None - Prefetching is not enabled.
Note: This is different from the prefetch argument, which
indicates whether or not the optimizer expects a prefetch to be done.
Run time is not influenced by the prefetch argument.
- All - All pages of the index or table are expected to be
read. The decision about whether to do a prefetch is made at run
time.
- A positive number - Indicates how many pages are expected to be
read. The closer this number is to zero, the more the prefetch quantity
will be reduced, or prefetch will not be done at all.
- Lock intents
- The lock modes that DB2 uses to access the data for the table, and
optionally to access individual rows. Lock modes include share,
exclusive, update, or next_key_share. They determine the level of
concurrency that is possible. (Displayed if the scan is over the base
table.)
For more information, see the section on locking in the Administration
Guide.
- Intra-partition scan type
- Indicates if the index scan is performed in parallel by each subagent or
if each subagent performs a private index scan.
- None - A private index scan.
- Local parallel - The index scan is performed in parallel by
each subagent.
(This item is displayed only for intra-partition parallelism or full
parallelism (intra-partition and inter-partition)).
- Intra-partition scan unit
- The scan granularity unit. That is, when the value of
Intra-partition scan type is set to Local parallel, the
assigned range is scan granularity number of scan
units.
- Page - Each subagent gets scan granularity pages at a
time.
- Row - Each subagent gets scan granularity rows at a
time.
(This item is displayed only for intra-partition parallelism or full
parallelism (intra-partition and inter-partition)).
(This item is available in Full details mode only.)
- Intra-partition scan granularity
- The number of scan units that a subagent is assigned when the value of
Intra-partition scan type is set to Local
parallel. (This item is displayed only for intra-partition
parallelism or full parallelism (intra-partition and inter-partition)).
(This item is available in Full details mode only.)
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