Install Fedora 21

This article presents how to install Fedora 21 – Live Workstation version.

I assume you have already downloaded Fedora 21 64 bit Live Workstation(about 1,37 G) and you know how to use VirtualBox 64 bit(100M). Create virtual machine with default settings for Linux Fedora 64 bit. 2GB ram and 64G(includes extra space for Oracle installations) for disk is enough plus increase video memory to 128M. Rest of options you can keep default.


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Configure physical standby database Oracle Database 12C release 1 (12.1)

This article presents how to configure physical standby database for Oracle Database 12C release 1 (12.1). It’s not focusing on transportation method, duplication method, protection modes nor extra functionality available for physical standbys. All above will be part of future articles :).

This presentation is based on the following article Install Oracle 12C Release 1 (12.1) on Oracle Linux 6 (OEL6).


Final standby configuration is very simple:

  • one host: – already configured with latest binaries Oracle Database 12C
  • primary database: ORA12C – already installed container database has one pluggable database PORA12C1 and SEED template database
  • listener LISTENER – already installed
  • standby database: SORA12C – this article shows how to configure it
  • standby configuration will work in default mode MAXIMUM PERFORMANCE


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ORA-00845: MEMORY_TARGET not supported on this system

During installation of Oracle you can encounter typical error commonly know by DBAs

ORA-00845: MEMORY_TARGET not supported on this system

Oracle is using for automatic memory management Linux shared segments. Usually they are too small but you can modify it on-the-fly.

Just modify entry in “/etc/fstab” to have persistent settings between reboot of your machine. Here shared segments are set to 2500M.

tmpfs   /dev/shm   tmpfs  size=2500M  0 0

remount it

mount -o remount tmpfs

and verify

mount | grep tmpfs
tmpfs on /dev/shm type tmpfs (rw,size=2500M)

to see what is using shared segments run following command

[oracle@oel6 ~]$ ipcs -m

------ Shared Memory Segments --------
key        shmid      owner    perms  bytes  nattch  status      
0x00000000 158433298  oracle   640    4096   0      
0x00000000 158466067  oracle   640    4096   0      
0x00000000 158498836  oracle   640    4096   0      
0x9d984658 158531605  oracle   640    12288  49

Have a fun :)

RMAN backup restore large files Oracle Database 12C release 1 (12.1)

There are two important improvements in making big datafile backups and restores in Oracle 12C release 1

  • multisection backup of image copies
  • multisection backup of incremental backups for level higher than 0

Multisection option was introduced in 11G and possible only for:

  • multisection backup of backup sets
  • multisection backup of full backup
  • multisection backup of incremental backups for level 0

Requirements and restrictions

  • COMPATIBLE must be set to 12.0 or higher
  • Not for control files or spfiles

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Session sequence Oracle Database 12C release 1 (12.1)

In Oracle Database 12C new keywords SESSION, GLOBAL are available that can be specified during a sequence creation


GLOBAL – creates standard sequence well known in previous release. This is the default.

SESSION – creates new type session sequence, which is a special type of sequence that is specifically designed to be used with global temporary tables that have session visibility.  Session sequence returns a unique range of sequence numbers only within a session, but not across sessions. Another difference is that session sequences are not persistent. If a session goes away, so does the state of the session sequences that were accessed during the session.

Session sequences must be created by a read-write database but can be accessed on any read-write or read-only databases (either a regular database temporarily open read-only or a standby database).

CACHE, NOCACHE,NOORDER are ignored when specified with SESSION calues

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RMAN separation of duties Oracle Database 12C release 1 (12.1)

In 12C release 1 Oracle has introduced new administrative privilege SYSBACKUP. It’s less powerful than SYSDBA:

  • it enables to execute backup and restore commands in rman
  • it enables to start stop the database
  • it’s more restrictive – it hasn’t got SELECT ANY TABLE privilege

During installation of oracle database binaries the privilege is associated with OS group backupdba.

Example of adding oracle dedicated groups

#groups for database management
groupadd -g 54321 oinstall
groupadd -g 54322 dba
groupadd -g 54323 oper
groupadd -g 54324 backupdba
groupadd -g 54325 dgdba
groupadd -g 54326 kmdba
groupadd -g 54327 asmdba
groupadd -g 54328 asmoper
groupadd -g 54329 asmadmin
add user Oracle for database software
useradd -u 54321 -g oinstall -G dba,oper,backupdba,dgdba,kmdba oracle

when installation of binaries is going on automatically new group is recognized


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APPROX_COUNT_DISTINCT – fast count distinct values Oracle Database 12C release 1 (12.1)

APPROX_COUNT_DISTINCT is new function available since version It returns approximate number of rows that contain distinct values of expr.


It’s alternative to the COUNT (DISTINCT expr) function, which returns the exact number of rows that contain distinct values of expr.

For processing large amounts of data it’s significantly faster than COUNT, with negligible deviation from the exact result.

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