Friday 20 March 2015

RAC BG PROCESS

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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