RAC Background Processes
Lock
Monitor Processes (LMON)
Lock
Monitor Services (LMS)
Lock
Monitor Daemon Process ( LMD)
LCKn
( Lock Process)
DIAG
(Diagnostic Daemon)
1. Lock Monitor Processes (LMON)
LMON Maintains GCS memory structures.
LMON handles the abnormal termination of
processes and instances.
LMON deals with Reconfiguration of locks
& resources when an instance joins or leaves the cluster (During
reconfiguration LMON generate the trace files)
LMON is responsible for executing dynamic
lock remastering every 10 mins ( Only in 10g R2 & later versions).
LMON Processes manages the global locks
& resources.
It monitors all instances in cluster,
primary for dictionary cache locks, library cache locks & deadlocks on
deadlock sensitive on enqueue & resources.
LMON also provides cluster group
services.
It is also called as GES [Global
Enqueue Service] monitor.
2. Lock Monitor Services (LMS)
Of all Background processes, LMS is
the most active
It consumes significant amount of CPU
time. (10g R2: Ensure that LMS process does not encounter the CPU starvation).
Its primary job is to transport
blocks across the nodes for cache-fusion requests.
When there is a consistent-read
request, the LMS process rolls back the block, makes a Consistent-Read image of
the block and then ships this block across the HSI (High Speed Interconnect) to
the process requesting from a remote node.
LMS also constantly checks with the
LMD background process (or our GES process) to get the lock requests placed by
the LMD process.
Each node will have 2 or more LMS
processes.
GCS_SERVER_PROCESSES parameter
denotes the number of LMS processes specified in init. ora file.
The above parameter value is set
based on number of cpu’s (MIN(CPU_COUNT/2,2))
In10gR2, for a single CPU instance,
only one LMS processes started.
It is advised to Increase the
parameter value, if global cache activity is very high.
Also called the GCS (Global Cache
Services) processes.
Internal View: X$KJMSDP
3. Lock Monitor Daemon Process (
LMDn)
LMD process performs lock and
deadlock detection globally.
It also monitors for lock conversion
timeouts.
Sometimes, it is also referred to as
the GES (Global Enqueue Service) daemon since its job is to manage the global
enqueue and global resource access.
LMD process also handles deadlock
detection and remote enqueue requests.
Remote resource requests are the
requests originating from another instance.
Internal View: X$KJMDDP
4. LCKn (Lock Process)
It manages instance resource requests
& cross instance calls for shared resources.
During instance recovery, it builds a
list of invalid lock elements and validates lock elements.
5. DIAG (Diagnostic Daemon)
A new background process introduced in
Oracle 10g featuring new enhanced diagnosability framework
Regularly monitors the health of the
instance.
Also checks instance hangs &
deadlocks.
It captures the vital diagnostics data
for instance & process failures.
QUICK REFERENCE:
RAC – Real Application Cluster
GCS – Global Cache Services
GES - Global Enqueue Service
LMD – Lock Monitor Deamon
LMON – Lock Monitor Processes
LMS – Lock Monitor Services
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