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CHAPTER 5 Implement: Making Required Application Changes

• Bulk copy into data-only-locked tables requires the version of

bcp and the

bulk copy libraries shipped with Adaptive Server version 11.9.2. Older

versions of

bcp and the bulk-copy libraries can still be used to copy into

allpages-locked tables. See the Release Bulletin for the required version

number.

• When using parallel sort for data-only-locked tables, the number of

worker processes must be configured to equal or exceed the number of

partitions, even for empty tables. The database option

select

into/bulkcopy/pllsort

must also be enabled.

Clustered indexes on data-only-locked tables may not return rows in clustered

key order if there is no order by clause. Bulk copy is not guaranteed to copy out

a table in clustered key order.

Queries on unpartitioned allpages-locked tables with clustered indexes return

rows in the clustered key order if the query does not include a sort (that is, if

there are no clauses such as order by or distinct). Bulk copy also copies the

rows out of allpages-locked tables in clustered key order for both partitioned

and unpartitioned tables.

Changes to Table-Level Locking

Performing an update or delete via a table scan does not acquire a table-level

exclusive lock as it did in earlier versions. In version 11.9.2, the scan acquires

an exclusive intent table lock when the transaction starts. When the scan locates

a row that must be updated, it acquires an exclusive page or row lock,

depending on the locking scheme. The only exception is an unindexed update

or delete to a data-only-locked table at transaction isolation level 3; these

updates acquire an exclusive table lock. In previous versions, any update or

delete that does not use an index acquires a table-level exclusive lock at the

start of the transaction.

In most cases, performing the scan without using a table level lock increases

concurrency. However, some applications may experience one of these

problems:

• Applications that did not deadlock in earlier versions may experience

deadlocks in 11.9.2.

• Tasks that update a large number of rows may use a large number of locks

if they cannot perform lock promotion due to conflicting locks.

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Seagate ST43401N/ND Guida di Installazione Pagina 49