Waits, Enqueues, and Latches - Expert Oracle RAC Performance Diagnostics and Tuning - page 591

Script: MVRACPDnTap_dlmrowcache.sql
SELECT inst_id INT,
parameter,
dlm_requests,
dlm_conflicts,
dlm_releases
FROM gv$rowcache
WHERE dlm_requests > 1000
ORDER BY inst_id,
dlm_requests desc,
dlm_conflicts desc;
In PARAMETER DLM_REQUESTS DLM_CONFLICTS DLM_RELEASES
---- -------------------------- ------------ ------------- ------------
1 dc_histogram_defs 8429505 61653 1917642
dc_objects 1507367 14260 511584
dc_segments 1246299 10924 377148
outstanding_alerts 851238 413316 5270
dc_tablespace_quotas 520598 27608 215
dc_sequences 46137 5052 410
dc_constraints 14669 89 1017
dc_users 4713 12 4512
2 dc_histogram_defs 3349862 69089 1284916
dc_objects 1083807 13353 706857
dc_segments 1016777 10883 556050
outstanding_alerts 848524 416058 1172
dc_tablespace_quotas 332066 24337 134
dc_sequences 31688 3808 325
dc_constraints 12665 118 821
dc_users 4000 21 3764
CF—Control File Transaction
The CF enqueue is placed by Oracle during any operation that requires reading or making changes to the control file.
CF enqueues are used to serialize control file transactions and read write operations on shared operations of the
control file. This is more prominently visible in a RAC environment when multiple instances share one control file
and need to update/write to the control file when there are structure changes to the database such as adding
tablespace and or datafile, during redo log switch or checkpoint, and during startup and shutdown of the database.
The SCN information for all transactions required for data recovery and the master SCN number is also managed
and maintained in the control file.
Waits
A wait event in Oracle is a situation when a session puts itself to sleep to wait for some external event to happen.
Wait events are classified based on what resource level the wait has occurred at: system, service, CPU, and so forth.
Wait events can also be classified based on what type of resource it's waiting for; idle waits occur when a session
is waiting for a work request to be issued. Non-idle or Service wait events are waits for the system to perform
asynchronous operations such as I/O or process creation.