Friday, March 25, 2011

- Oracle 11g Automatic Memory Management (AMM) --

Let's start with a brief introduction to basic concepts.

PROGRAM GLOBAL AREA (PGA): is a region that contains data and control information for a server process, this is non shared memory created by the database when a server process is started and access is exclusive to the particular server process.SH
SHARED_GLOBAL_AREA (SGA) :  Is a group of memory structures that contain data and control information for the Oracle instance, it is shared by all background processes.

Oracle has made great progress to simplify memory management through the last versions of the RDBMS. In 9i they introduced PGA management, in 10g they automated the SGA management and in 11g you can manage both (PGA and SGA) with a single configuration using "Automatic Memory Management (AMM)". AMM allows you to allocate a chunk of memory which Oracle uses to manage both SGA and PGA, AMM uses 2 parameters:

MEMORY_TARGET: Amount of memory available to Oracle to use dynamically to control SGA and PGA, this is the amount of memory Oracle will allocate when you start the database to manage PGA and SGA.

MEMORY_MAX_TARGET: Maximum amount of memory that Oracle can use, when no specified the max is equal to MEMORY_TARGET.

When  AMM is in use, SGA_TARGET (Introduced in 10g) and PGA_AGGREGATE_TARGET (Introduced in 9i)  act as the minimum size setting for their respective areas. It is recommend to set this to 0 when using AMM so Oracle can take full control of it.

Thursday, March 3, 2011

-- How to map disk devices to physical devices in Solaris --

You can map between the two device naming conventions using a script like the one below.

Instance Names: Instance names refer to the nth device in the system (for example, sd20).

Instance names are occasionally reported in driver error messages. You can determine the binding of an instance name to a physical name by looking at dmesg(1M) output, as in the following example.

sd9 at esp2: target 1 lun 1 sd9 is /sbus@1,f8000000/esp@0,800000/sd@1,0

Once the instance name has been assigned to a device, it remains bound to that device.

Instance numbers are encoded in a device's minor number. To keep instance numbers consistent across reboots, the system records them in the /etc/path_to_inst file.

!/usr/bin/env perl

use strict;

my @path_to_inst = qx#cat /etc/path_to_inst#;
map {s/"//g} @path_to_inst;
my ($device, $path, @instances);

for my $line (qx#ls -l /dev/dsk/*s2#) {
    ($device, $path) = (split(/\s+/, $line))[-3, -1];
    $path =~ s#.*/devices(.*):c#$1#;

    @instances =
        map {join("", (split /\s+/)[-1, -2])}
            grep {/$path/} @path_to_inst;
*emphasized text*
    for my $instance (@instances) {
        print "$device $instance\n";

Tuesday, February 15, 2011

-- Oracle TAF server side not properly configured using srvctl due to bug 6886239 --

Oracle alerted us recently of a non public bug #6886239 "DBMS_SERVICE parameters are not added using srvctl add service. It affects 10g and 11gR1 databases, this is fixed in release 11.2 onwards. In Oracle RAC after setting up TAF although it does not fails and everything looks good, it does not configure correctly.

When you check the service configuration you find no values for failover method, type and retries, those values are needed for TAF to happen.

Creating a service

srvctl add service -d rac -s server_taf -r "rac1,rac2" -P BASIC

Start the service

srvctl start service -d rac -s server_taf

Checking that the services are running.

srvctl config service -d rac

ractest PREF: rac1 rac2 AVAIL:
server_taf PREF: rac1 rac2 AVAIL:

Getting the service ID value

sqlplus /nolog
Connect / as sysdba
SQL> select name,service_id from dba_services where name = 'server_taf';
---------------------------------------------------------------- ----------
server_taf 6

Checking the setup

SQL>col name format a15
col failover_method format a11 heading 'METHOD'
col failover_type format a10 heading 'TYPE'
col failover_retries format 9999999 heading 'RETRIES'
col goal format a10
col clb_goal format a8
col AQ_HA_NOTIFICATIONS format a5 heading 'AQNOT'
SQL>select name, failover_method, failover_type, failover_retries,goal, clb_goal,aq_ha_notifications
from dba_services where service_id = 6
--------------- ----------- ---------- -------- ---------- -------- -----
server_taf LONG NO

Adding the server side failover parameter to the service

Server side TAF method is BASIC. BASIC is the only value currently supported. This means that a new connection is established at failure time. It is not possible to pre-establish a backup connection. (which is to say, PRECONNECT is not supported)

SQL> execute dbms_service.modify_service (service_name => 'server_taf' -
, aq_ha_notifications => true -
, failover_method => dbms_service.failover_method_basic -
, failover_type => dbms_service.failover_type_select -
, failover_retries => 180 -
, failover_delay => 5 -
, clb_goal => dbms_service.clb_goal_long);
PL/SQL procedure successfully completed.

Check that the service can now see the values for methods, types and retries

SQL>select name, failover_method, failover_type, failover_retries,goal, clb_goal,aq_ha_notifications
from dba_services where service_id = 6
--------------- ----------- ---------- -------- ---------- -------- -----

Check that the listener has the service registered

lsnrctl services

Create a net service name. Here we have client load balancing between the two nodes.

(ADDRESS = (PROTOCOL = TCP)(HOST = dell01)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = dell02)(PORT = 1521))

You are all set now :-