Daylight saving time support in Oracle CRS

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In this post, I want to share my experience of how I solved the daylight saving time problem with Oracle CRS. With the default setup, in case timezone changes on your system, the client/application who connects to the database remotely(local/BEQ connections have correct timezone) will still have old timezone information and will enter wrong data.

Some countries,  that are not affected by daylight saving time are lucky and does not have to worry about it. But if your servers are not located in lucky countries then you must make CRS DTS aware.

During the GI installation, Oracle saves Timezone information in $CRS_HOME/crs/install/s_crsconfig_hostname_env.txt file, that makes TZ not to change for CRS even it is changed on OS level.

Please note that timezone can be changed for the database using srvctl:

srvctl setenv database -env 'TZ=time zone'

But I do not recommend to do that, because you must do the same everytime you create a new database.
Better to change TZ globally at CRS level.

In simple words just commenting out the TZ variable in $CRS_HOME/crs/install/s_crsconfig_hostname_env.txt and restarting the CRS on each node just one time is enough to do that, but let’s check it.

1.  List the current timezone settings:

[root@rac1 ~]# timedatectl status|grep zone
Time zone: UTC (UTC, +0000)
[root@rac2 ~]#  timedatectl status|grep zone
Time zone: UTC (UTC, +0000)

2. Change timezone at OS level:

[root@rac1 ~]# timedatectl set-timezone Europe/Bratislava
[root@rac2 ~]# timedatectl set-timezone Europe/Bratislava

3. Check local and scan connections:

[oracle@rac1 ~]$ sqlplus / as sysdba

SQL> select to_char(sysdate,'HH24:MI:SS AM')  dbtime from dual;

DBTIME
-----------
18:50:05 PM     <<<<<<<<<<<<Correct , same as OS

[oracle@rac1 ~]$ sqlplus marik/123@ORCL

SQL> select to_char(sysdate,'HH24:MI:SS AM') dbtime from dual;

DBTIME
-----------
16:50:10 PM     <<<<<<<<<<<<Incorrect

4. Comment TZ in the config file:

[root@rac1 ~]# cat /u01/app/18.3.0/grid/crs/install/s_crsconfig_rac1_env.txt|grep TZ=
#   the appropriate time zone name. For example, TZ=America/New_York
#TZ=UTC

[root@rac2 ~]# cat /u01/app/18.3.0/grid/crs/install/s_crsconfig_rac2_env.txt|grep TZ=
#   the appropriate time zone name. For example, TZ=America/New_York
#TZ=UTC

5. Restart CRS on both nodes:

[root@rac1 ~]#  crsctl stop crs
[root@rac1 ~]#  crsctl start crs -wait
[root@rac2 ~]#  crsctl stop crs
[root@rac2 ~]#  crsctl start crs -wait

6. Change timezone on OS level several times and check local & scan connections:

[root@rac1 ~]# timedatectl set-timezone Africa/Conakry
[root@rac2 ~]# timedatectl set-timezone Africa/Conakry

Important: You need to reconnect to the database(so consider that sessions must be disconnected and reconnected again, old connections have old settings)

[oracle@rac1 ~]$ sqlplus / as sysdba

SQL> Select to_char(sysdate,'HH24:MI:SS AM') dbtime from dual;

DBTIME
-----------
17:15:56 PM <<<<<<<<<<<<Correct


[oracle@rac1 ~]$ sqlplus marik/123@ORCL

SQL> Select to_char(sysdate,'HH24:MI:SS AM') dbtime from dual;

DBTIME
-----------
17:15:27 PM <<<<<<<<<<<<Correct

Change one more time:

[root@rac1 ~]# timedatectl set-timezone America/Aruba
[root@rac2 ~]# timedatectl set-timezone America/Aruba

Exit connections and reconnect:

[oracle@rac1 ~]$ sqlplus / as sysdba

SQL> Select to_char(sysdate,'HH24:MI:SS AM') dbtime from dual;

DBTIME
-----------
13:17:47 PM <<<<<<<<<<<<Correct

[oracle@rac1 ~]$ sqlplus marik/123@ORCL

SQL> Select to_char(sysdate,'HH24:MI:SS AM') dbtime from dual;

DBTIME
-----------
13:17:31 PM <<<<<<<<<<<<Correct