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In an Oracle RAC instance, several additional processes are started to
manage the RAC locks and provide for the intra-node communications. In
addition, a lock area is added to the SGA. These processes and structures
are:
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LMON -- The background Global Enqueue Service Monitor (LMON) monitors
the entire cluster to manage global resources. LMON manages instance and
process failures and the associated recovery for the Global Cache Service
(GCS) and Global Enqueue Service (GES). In particular, LMON handles the part
of recovery associated with global resources. LMON-provided services are
also known as cluster group services (CGS)
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LCKx -- The LCK process manages instance global enqueue requests and
cross-instance call operations. Workload is automatically shared and
balanced when there are multiple Global Cache Service Processes (LMSx).
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LMSx -- The Global Cache Service Processes (LMSx) are the processes
that handle remote Global Cache Service (GCS) messages. Current Real
Application Clusters software provides for up to 10 Global Cache Service
Processes. The number of LMSx varies depending on the amount of messaging
traffic among nodes in the cluster. The LMSx handles the acquisition
interrupt and blocking interrupt requests from the remote instances for
Global Cache Service resources. For cross-instance consistent read requests,
the LMSx will create a consistent read version of the block and send it to
the requesting instance. The LMSx also controls the flow of messages to
remote instances.
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LMDx --The Global Enqueue Service Daemon (LMD) is the resource agent
process that manages Global Enqueue Service (GES) resource requests. The LMD
process also handles deadlock detection Global Enqueue Service (GES)
requests. Remote resource requests are requests originating from another
instance.
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ORACM -- Oracle Cluster Manager process -- Cluster Manager is an
Operating System-Dependent component that discovers and tracks the
membership state of nodes by providing a common view of cluster membership
across the cluster. CM monitors process health. The LMON process, a
background process that monitors the health of the Global Cache Service
(GCS), registers and de-registers from the CM. The CM also manages recovery
from any network card or cable failures.
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GSD -- The Global Services Daemon (GSD) is a component that receives
requests from SRVCTL to execute administrative job tasks such as startup or
shutdown. The command is executed locally on each node and the results are
sent back to SRVCTL. The daemon is installed on the nodes by default and
should not be deleted. You may wonder why this precaution is necessary. In
versions prior to 9.2.0.1, the letters "GSD" appeared nowhere in the
UNIX/LINUX process name shown by a ps -ef command so unwitting system
administrators and DBAs could unknowingly delete this critical process. Even
in the latest release, some versions of UNIX/LINUX only show a
length-restricted version of the process name string and may not allow a ps
-ef|grep gsd command to identify the daemon process. Since multiple versions
of some of the Oracle support processes (such as the dbsnmp process) may
appear due to bugs in early releases, take great care when deleting Oracle
related processes. Be sure to leave any starting with your ORACLE_BASE and
containing jre in the path, as one of these is your GSD daemon.
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DIAG -- The diagnose daemon is a Real Application Clusters background
process that captures diagnostic data on instance process failures. No user
control is required for this demo.
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GCS -- This is the main controlling process for cache fusion. It
tracks the location and status (mode and role) of the data blocks, as well
as the access privileges of the various instances. GCS guarantees data
integrity by employing global access levels. It maintains block modes for
data blocks in the global role. It is also responsible for block transfers
between instances. As shown in Fig. 7.2, upon a request from an instance,
GCS organizes the block shipping and the appropriate lock mode conversions.
Various background processes, such as global cache service processes (LMSn)
and the global enqueues service daemon (LMD), implement the global cache
service.
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