Which two statements are true about Active Session History (ASH)?(Choose two.)
A.
The Data Sample size available in an ASH report is dynamic and, at any given moment,
is directly related to the amount of work being performed.
B.
ASH contains sampled data from all sessions that are connected to a database instance at
any given moment.
C.
ASH samples data from V$SESSION every second.
D.
An ASH report can be used to identify the service that may be the cause of a transient
performance problem.
A,D
A,D
C is correct too:
https://books.google.it/books?id=xxx0KAwY_ZMC&pg=PA845&lpg=PA845&dq=samples+data+from+V$SESSION+every+second&source=bl&ots=4FrjANs-0x&sig=MzP2SCpCEi57sXY1iGX2AlIJZiU&hl=it&sa=X&ved=0ahUKEwiUsvLK8vvSAhWD8RQKHQePB4wQ6AEIRjAF#v=onepage&q=samples%20data%20from%20V%24SESSION%20every%20second&f=false
so ..? what between A,C,D ?
I don’t think that ASH samples v$session EVERY SECOND.
So C is not correct.
CD
Performance Management Tuning 12c – Student Guide (7-32):
It would be very expensive to record all activities of all sessions. The ASH extracts only samples of information from V$SESSION. One sample is extracted every second.
indeed duong
Yes I swear : every second in V$ACTIVE_SESSION_HISTORY and then sampled to 1/10 to DBA_HIST8ACTIVE_SESS_HISTORY
A may deal with the ASH buffer wich is circular and “fixed size”. So when it is full, it is sampled to DBA_HIST_ACTIVE_SESS_HISTORY.
So A would be typically wrong : sample size does not depend on workload
So CD
C,D
https://docs.oracle.com/cloud/latest/db112/REFRN/dynviews_1007.htm#REFRN30299
” It contains snapshots of active database sessions taken once a second. ”
“SERVICE_HASH NUMBER Hash that identifies the Service; maps to V$ACTIVE_SERVICES.NAME_HASH”