Oracle9i RAC Additional Processes

August 28,  2003
Don Burleson
 

In an Oracle9i 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:

• 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)

• 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).

• 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.

• 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.

• 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.

• 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 Oracle9i 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.

• 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.

• 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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