Which two recommendations may reduce this problem?

You notice that there is a very high percentage of wait time for the enq:HW-contention event in
your RAC database that has frequent insert operations.
Which two recommendations may reduce this problem?

A.
shorter transactions

B.
increasing sequence cache sizes

C.
using reverse key indexes

D.
uniform and large extent sizes

E.
automatic segment space management

F.
smaller extent sizes

Explanation:
Segments have High Water Mark (HWM) indicating that blocks below that HWM
have been formatted. New tables or truncated tables [that is truncated without reuse storage
clause], have HWM value set to segment header block. Meaning, there are zero blocks below

HWM. As new rows inserted or existing rows updated (increasing row length), more blocks are
added to the free lists and HWM bumped up to reflect these new blocks. HW enqueues are
acquired in Exclusive mode before updating HWM and essentially HW enqueues operate as a
serializing mechanism for HWM updates. Allocating additional extent with instance keyword
seems to help in non-ASSM tablespace
Serialization of data blocks in the buffer cache due to lack of free lists, free list groups, transaction
slots (INITRANS), or shortage of rollback segments.
This is particularly common on INSERT-heavy applications, in applications that have raised the
block size above 8K, or in applications with large numbers of active users and few rollback
segments. Use automatic segment-space management (ASSM) and automatic undo management
to solve this problem.
HW enqueue The HW enqueue is used to serialize the allocation of space beyond the high water
mark of a segment.
If this is a point of contention for an object, then manual allocation of extents solves the problem.