Database Reference
In-Depth Information
needs to grow, while the enqueue TX is used to serialize write access to rows and the interested
transaction list (ITL) at the beginning of a database block.
In Oracle10 g , the fixed view V$ENQUEUE_STATISTICS may be used to generate a list of
208 enqueue types and names along with descriptions and one or more reasons why each enqueue
may be requested. Table 27-2 contains such a list for some of the more common enqueue types.
Table 27-2. Enqueue Types
Enqueue
Type
Name
Description
Reason for
Getting Enqueue
CF
Controlfile
Transaction
Synchronizes accesses to the control file
contention
CI
Cross-Instance
Call Invocation
Coordinates cross-instance
function invocations
contention
DX
Distributed
Transaction
Serializes tightly coupled distributed
transaction branches
contention
HV
Direct Loader
High Water Mark
Lock used to broker the high water mark
during parallel inserts
contention
HW
Segment High
Water Mark
Lock used to broker the high water mark
during parallel inserts
contention
JQ
Job Queue
Lock to prevent multiple instances from
running a single job
contention
JS
Job Scheduler
Lock to prevent job from running elsewhere
job run
lock-synchronize
JS
Job Scheduler
Lock to recover jobs running on crashed
RAC inst
job recov lock
JS
Job Scheduler
Lock on internal scheduler queue
queue lock
JS
Job Scheduler
Scheduler non-global enqueues
sch locl enqs
JS
Job Scheduler
Lock obtained when cleaning up
q memory
q mem clnup lck
JS
Job Scheduler
Lock got when adding subscriber to
event q
evtsub add
JS
Job Scheduler
Lock got when dropping subscriber to
event q
evtsub drop
JS
Job Scheduler
Lock got when doing window open/close
wdw op
JS
Job Scheduler
Lock got during event notification
evt notify
JS
Job Scheduler
Synchronizes accesses to the job cache
contention
SQ
Sequence Cache
Lock to ensure that only one process can
replenish the sequence cache
contention
SS
Sort Segment
Ensures that sort segments created during
parallel DML operations aren't prematurely
cleaned up
contention
ST
Space Transaction
Synchronizes space management activities
in dictionary-managed tablespaces
contention
 
Search WWH ::




Custom Search