Database Reference
In-Depth Information
CHAPTER 34
■ ■ ■
Removing the RAC Option
Without Reinstalling
O
racle Real Application Clusters (RAC) can only operate if an instance of Oracle's own cluster
software, which is mandatory starting from Oracle10
g
, or a so-called vendor cluster software is
available on the same node as the Oracle DBMS instance. This chapter explores the impact of
cluster software failure, which in turn prevents RAC instances from opening a database.
Oracle's cluster software uses a so-called Cluster Registry to save configuration information. It
also writes special messages to voting disks to orchestrate cluster actions after an interconnect
network failure. In cases of an emergency, such as the loss of all voting disks or the failure of all
devices holding copies of the Cluster Registry, Oracle Clusterware cannot be started. In such a
severe fault scenario, it might take hours or even days to attach new SAN (Storage Area Network)
storage to the system, create logical units (LUNs) in the SAN disk array, and configure zoning
to make the LUNs visible to the database server. Oracle Clusterware may cause unjustified
node reboots and thus unplanned downtime, although it has matured tremendously since the
early days. This might be another reason for disabling RAC. This chapter explains how to use
an undocumented
make
command to remove the RAC option from the
oracle
executable. Since
ASM cannot run at all without Oracle Clusterware infrastructure, a procedure that converts an
Oracle Clusterware installation for RAC to a local-only Oracle Clusterware installation for use
with single-instance ASM is shown. Thus, a system running RAC can quickly be converted to a
system running single instance ORACLE without reinstalling any software with Oracle Universal
Installer (OUI) and patching an ORACLE_HOME with OPatch, greatly reducing the downtime
incurred by such a severe outage.
Linking ORACLE Software
When ORACLE Server software is installed on a UNIX system by OUI, many programs, including
$ORACLE_HOME/bin/oracle
, which implements the database kernel, are linked with static and
shared libraries on the system. OUI calls the utility
make
and passes it the makefile
$ORACLE_HOME/
rdbms/lib/ ins_rdbms.mk
as an argument. Other makefiles such as
$ORACLE_HOME/network/lib/
ins_net_server.mk
are used to link Oracle Net components and still others to link SQL*Plus,
and so on.
Similar steps occur when a patch set (OUI) or interim patch (OPatch) is applied. Most
patches modify a static library in
$ORACLE_HOME/lib
by replacing an object module with a newer
version that includes a bug fix. The executable
oracle
must be relinked to pick up a changed
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