||Oracle Tips by Burleson
Oracle10g Grid Computing
Chapter 12 - RAC Design Considerations
Setting dml_locks to Zero
checks the flag to ensure that there is not a non-parallel direct load
running against the same table. The use of direct load forces Oracle
to create new extents for each session.
If dml_locks are set to
zero on one instance, then it must be set it to zero on all instances.
If non-zero values are used with the dml_locks parameter, the values
need not be identical on all instances.
Performance for Object Creation in Real Application Clusters
Oracle database, DDL statements should be used for maintenance tasks,
not during normal system operations. For example, use global temporary
tables or PL/SQL tables rather than permanent tables for reports. If
this guideline is followed, in most systems, the frequency of DDL
statements should be low.
application has to create objects frequently, performance degradation
to the RAC environment will occur. This is due to the fact that object
creation requires inter-instance coordination. A large ratio of
the dc_object_idsrow cache in
v$rowcache (the same
select as was used for sequences will work here as well), along with
excessive wait times for the row cache lock event in v$system_event, is
indicative that multiple instances in the cluster are issuing
excessive amounts of concurrent DDL statements.
only method to improve object creation performance in these situations
is to set event 10297 so that it caches OBJECT_ID values. This will
improve concurrent object creation by eliminating the recursive DDL
and some of the intra-instance pinging. To set event 10297, add the
following line to the initialization parameter file:
trace name context forever, level 1"
additional level argument is set to 1, then the caching behavior is
automatically adjustable internally. Otherwise, the level can be set
to the desired cache size.
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