Seagate ST43401N/ND Guía de instalación descargar pdf (Pagina 61)

CHAPTER 5 Implement: Making Required Application Changes

select * from lineitem, part

where ((p_partkey = l_partkey and l_quantity >= 10)

or (p_partkey = l_partkey and l_quantity <= 20) )

becomes

select * from lineitem, part

where ((p_partkey = l_partkey and l_quantity >= 10)

or (p_partkey = l_partkey and l_quantity <= 20) )

and (p_partkey = l_partkey)

and (l_quantity >= 10 or l_quantity <= 20)

The addition of the conjuncts adds usable SARGs for the optimizer. If new

conjuncts (

and clauses) added by predicate transformation and factoring are

found not to be useful as part of index access strategy (that is, for filtering) they

are not used.

Query semantics do not change.The result set is the same. Predicate factoring

cannot be turned off. It is completely transparent to the user. It is implemented

as a new compiler phase, just before the start of the optimizer.

When it happens, trace flag 302 output shows additional costing blocks and

showplan shows additional “Keys are” messages.

50 Tables in a Query

ASE now supports up to 50 user tables and 14 worktables. This is up from 16

user tables and 12 worktables in 11.9.2. Bear in mind, however, the limits on

number of referential integrity checks remain at 192 and the number of

subqueries allowed remains at 16.

Abstract Query Plans

Abstract plans were introduced in release 12.0 as a means for system

administrators and performance tuners to protect the overall performance of a

server from changes to query plans. Changes in query plans may be due to:

• Adaptive Server software upgrades that affect optimizer choices

• New Adaptive Server features that change query plans

• Changing tuning options such as the parallel degree, table partitioning, or

indexing

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Seagate ST43401N/ND Guía de instalación Pagina 61