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Server Administration, Performance Tuning

Oracle Wait EventsLatches and Latch ContentionHow To find The Row Which is Locked by a SessionSQL : Useful scripts for DBA

Oracle Real Application Clusters (RAC)

Oracle RAC Interview questionsRAC Load Balancing, TAF , FANWhen during the installation process are clusterware components createdSteps to move OCR and Voting disksteps to Restore RAC Database to Single InstanceStep to migrate crs resources to new server.

Backup & Recovery, RMAN

Steps to recover Primary's Datafile from StandbySteps to recover Standby after missing archivelogbackup-based duplication in 11GR2

Oracle 11g new features

11g New Features in Dataguard11g New Features in RMAN11g New Features - Invisible Indexes11g New Features for AMM11g New Features in datapump11g New Features Read only tables

Data Guard

Dataguard failover test with flashback

Server Utilities ..exp/imp , expdp , impdp, SQL*Loader ...

How to change the table name during import?

Oracle Wait Events

Before looking into wait events, let us understand various state of user process. 

Oracle user process is typically in one of the three states: 

a. Idle wait. e.g. 'SQL*Net message from client'

b. Running code - Either on CPU or on a run queue. Oracle itself does not know if it is on-

CPU or just on a run queue.

c. Waiting

i. for some resource to become available. e.g. enqueue (lock) or a latch

ii. for an activity to complete that it has requested. Like an IO read request.

Oracle has a set of 'Wait Events' for activities in 'a' and 'c', and record CPU utilization for

'b'. 

This is best illustrated with a simplified example of few seconds in the life of an Oracle

shadow process: 

State Notes...

~~~~~ ~~~~~~~~

IDLE : Waiting for 'SQL*Net message from client'. Receives a SQL*Net packet requesting

'parse/execute' of a statement

ON CPU : decodes the SQL*Net packet.

WAITING : Waits for 'latch free' to obtain the a 'library cache' latch Gets the latch.

ON CPU : Scans for the SQL statement in the shared pool, finds a match, frees latch ,

sets up links to the shared cursor etc.. & begins to execute.

WAITING : Waits for 'db file sequential read' as we need a block which is not in the

buffer cache. Ie: Waiting for an IO to complete.

ON CPU : Block read has completed so execution can continue. Constructs a SQL*Net

packet to send back to the user containing the first row of data.

WAITING : Waits on 'SQL*Net message to client' for an acknowledgement that the

SQL*Net packet was reliably delivered.

IDLE : Waits on 'SQL*Net message from client' for the next thing to do.

Most common wait events are..

Buffer Busy waits/Cache Buffers Chains Latch waits

•This wait happens when a session wants to access a database block in the buffer cache

but it cannot as the buffer is "busy". The two main cases where this can occur are: 

1.Another session is reading the block into the buffer 

2.Another session holds the buffer in an incompatible mode to our request 

Cache Buffers Chains Latch waits are caused by contention where multiple sessions

waiting to read the same block.

Typical solutions are:- 

Look at the execution plan for the SQL being run and try to reduce the gets per

executions which will minimise the number of blocks being accessed and therefore

reduce the chances of multiple sessions contending for the same block. 

Increase the PCTFREE for the table storage parameter. This will result in less rows per

block.

Consider implementing reverse key indexes. (if range scans aren't commonly used

against the segment)

In v$session_wait, the P1, P2, and P3 columns identify the file number, block number,

and buffer busy reason codes, respectively.

"Read By Other Session" wait event.

When user sessions request for data, Oracle will first read the data from disk into the

database buffer cache. If two or more sessions request the same data, the first session

will read the data into the buffer cache while other sessions wait. In previous versions,

this wait was classified under the "buffer busy waits" event. However, in Oracle 10g and

higher, this wait time is now broken out into the "read by other session" wait event. 

Excessive waits for this event are typically due to several processes repeatedly reading

the same blocks, e.g. many sessions scanning the same index or performing full table

scans on the same table. Tuning this issue is a matter of finding and eliminating this

contention. 

When a session is waiting on this event, an entry will be seen in the v$session_wait

system view giving more information on the blocks being waited for: 

SELECT p1 "file#", p2 "block#" 

FROM v$session_wait WHERE event = 'read by other session'; 

If information collected from the above query repeatedly shows that the same block (or

range of blocks) is experiencing waits, this indicates a "hot" block or object. 

The following query will give the name and type of the object: 

SELECT owner, segment_name, segment_type 

FROM dba_extents WHERE file_id = &file 

AND &block BETWEEN block_id AND block_id + blocks - 1 

Log File Sync waits

Log file sync waits occur when sessions wait for redo data to be written to disk. 

Typically this is caused by slow writes or committing too frequently in the application.

db file sequential read

Wait for an I/O read request to complete. A sequential read is usually a single-block

read. This differs from "db file scattered read" in that a sequential read reads data into

contiguous memory (whilst a scattered read reads multiple blocks and scatters them

into different buffers in the SGA). 

db file scattered read

This wait happens when a session is waiting for a multiblock IO to complete. This

typically occurs during full table scans or index fast full scans. Oracle reads up to

DB_FILE_MULTIBLOCK_READ_COUNT consecutive blocks at a time and scatters them

into buffers in the buffer cache.

direct path read

Direct path reads are generally used by Oracle when reading directly into PGA memory

(as opposed to into the buffer cache). 

This style of read request is typically used for: 

Sort I/Os when memory Sort areas are exhausted and temporary tablespaces are used

to perform the sort

Parallel Query slaves.

direct path write

This wait is seen for: 

Direct load operations (eg: Create Table as Select (CTAS) may use this)

Parallel DML operations 

Sort IO (when a sort does not fit in memory) 

db file parallel write

DBW waits on "db file parallel write" when waiting for a parallel write to files and blocks

to complete.

The db file parallel write occurs when the process, typically DBWR, has issued multiple

I/O requests in parallel to write dirty blocks from the buffer cache to disk, and is waiting

for all requests to complete. 

-------------------------------------------------- 

V$Session_wait_history 

From Oracle Database 10g a new view V$Session_wait_history will allow us to see the

last few wait events a session waited on.

The last 10 wait events that a session experienced can be displayed using the

v$session_wait_history view. The session has to be currently active. Once the session

ends this information is not available.

We can use the seq# column to sort the wait events into the order in which the wait

events occurred for the session.

Labels: Interview Questions : Wait Events

Latches and Latch Contention

What is a latch? 

Latches are low level serialization mechanisms used to protect shared data structures in

the SGA. A process acquires a latch when working with a structure in the SGA. It

continues to hold the latch for the period of time it works with the structure

A latch is a type of a lock that can be very quickly acquired and freed. 

Latches are typically used to prevent more than one process from executing the same

piece of code at a given time.

List of latches that are of most concern to a DBA 

BUFFER CACHE LATCHES: 

There are two main latches which protect data blocks in the buffer cache.

- Cache buffers chains latch :- This latch is acquired whenever a block in the buffer

cache is accessed. 

Cache Buffers Chains Latch waits are caused by contention where multiple sessions

waiting to read the same block.

Reduce logical I/O rates by tuning and minimizing the I/O requirements of the SQL

involved.

Identify and reduce the contention for hot blocks.

- Cache buffers LRU chain latch:- This latch is acquired in order to introduce a new

block into the buffer cache and when writing a buffer back to disk. 

Reduce contention for this by increasing the size of the buffer cache 

REDOLOG BUFFER LATCHES: 

- Redo allocation latch:- The redo allocation latch is acquired in order to allocate

space within the log buffer.

Increase the size of the LOG_BUFFER

Reduce the load of the log buffer using NOLOGGING features when possible. 

- Redo copy latch:-This latch is used to write redo records into the redolog buffer. 

Contention can be reduced by increasing the value of LOG_SIMULTANEOUS_COPIES in

multi-cpu system.

LIBRARY CACHE:

- Library cache latch:- The library cache latch must be acquired in order to add a new

statement to the library cache. - 

Ensure that the application is reusing as much as possible SQL statement.

If the application is already tuned, increase the SHARED_POOL_SIZE.

- Library cache pin latch:- This latch is acquired when a statement in the library

cache is reexecuted.

SHARED POOL RELATED LATCHES 

- Shared pool latch: While the library cache latch protects operations withing the

library cache, the shared pool latch is used to protect critical operations when allocating

and freeing memory in the shared pool. 

Ways to reduce the shared pool latch are, avoid hard parses when possible.

Row cache objects latch:- This latch comes into play when user processes are

attempting to access the cached data dictionary values. 

Reduce contention for this latch is by increasing the size of the shared pool

(SHARED_POOL_SIZE)

How To find The Row Which is Locked by a Session

Which row is locked in a certain table can only be queried when other session is waiting

for the row involved.

Check below link for the sql to find.

How To Identify The Row Which is Locked by a Session

Useful SQL Scripts

Useful SQL Scripts for day-to-day DBA tasks.

SQL to find the locked object and session that locked the object. 

Run below script when user complaints that update statement hangs...

column LOCKED_OBJECT format A35 wrapped

column ORACLE_USERNAME format A17 wrapped 

column OS_USER_NAME format A12 wrapped 

column SESSION_ID format 999999 wrapped 

column SINCE format A21 

select o.OWNER || '.' || o.OBJECT_NAME as LOCKED_OBJECT,

lo.ORACLE_USERNAME,

lo.OS_USER_NAME,

lo.SESSION_ID,

lo.PROCESS,

case lo.LOCKED_MODE

when 0 then 'none'

when 1 then 'null (NULL)'

when 2 then 'row-S (SS)'

when 3 then 'row-X (SX)'

when 4 then 'share (S)'

when 5 then 'S/Row-X (SSX)'

when 6 then 'exclusive (X)'

end as LOCKED_MODE,

cast(sysdate-(CTIME/(24*60*60)) as timestamp(0)) as SINCE

from DBA_OBJECTS o,

V$LOCKED_OBJECT lo,

V$LOCK l

where o.OBJECT_ID = lo.OBJECT_ID

and lo.OBJECT_ID = l.ID1 and lo.SESSION_ID = l.SID 

order by LOCKED_OBJECT, ORACLE_USERNAME, OS_USER_NAME, SESSION_ID;

------------------------------------------------------------------

When a session is waiting for lock, how to find the blocking session and

waiting for object and row ...

To find who is blocking ?

select sb.username || '@' || sb.machine

|| ' ( SID=' || sb.sid || ' ) is blocking '

|| sw.username || '@' || sw.machine || ' ( SID=' || sw.sid || ' ) ' AS blocking_status

from v$lock lb, v$session sb, v$lock lw, v$session sw

where sb.sid=lb.sid and sw.sid=lw.sid

and lb.BLOCK=1 and lw.request > 0

and lb.id1 = lw.id1

and lw.id2 = lw.id2 ;

Waiting for object and rowid ...

select o.object_name, row_wait_obj#,  row_wait_file#,  row_wait_block#,

row_wait_row#,

dbms_rowid.rowid_create ( 1, o.DATA_OBJECT_ID, ROW_WAIT_FILE#,

ROW_WAIT_BLOCK#, ROW_WAIT_ROW# )

from v$session s, dba_objects o where sid=&waiting_sid and s.ROW_WAIT_OBJ# =

o.OBJECT_ID ; 

  

Waiting for row.. 

  

select * from table_name_from_above where rowid =&rowid_returned 

  

------------------------------------------------------------ 

To check dataguard 

When you get alert that standby database is out of sync..

Run this at Primary

set pages 1000

set lines 120

column DEST_NAME format a20

column DESTINATION format a35

column ARCHIVER format a10

column TARGET format a15

column status format a10

column error format a15

select DEST_ID,DEST_NAME,DESTINATION,TARGET,STATUS,ERROR from v$archive_dest

where DESTINATION is NOT NULL

/

select ads.dest_id,max(sequence#) "Current Sequence",

max(log_sequence) "Last Archived"

from v$archived_log al, v$archive_dest ad, v$archive_dest_status ads 

where ad.dest_id=al.dest_id and al.dest_id=ads.dest_id group by ads.dest_id; 

Run this at Standby

select max(al.sequence#) "Last Seq Recieved" from v$archived_log al

/

select max(al.sequence#) "Last Seq Apllied" from v$archived_log al

where applied ='YES'

/

select process,status,sequence# from v$managed_standby

/

Note: This script won't work for RAC

-----------------------------------------------------------------------------------

To get hidden parameters values

-- must be run from SYS.

SELECT

a.ksppinm "Parameter",

a.ksppdesc "Description",

b.ksppstvl "Session Value",

c.ksppstvl "Instance Value"

FROM

sys.x$ksppi a,

sys.x$ksppcv b,

sys.x$ksppsv c

WHERE

a.indx = b.indx

AND

a.indx = c.indx

AND

a.ksppinm LIKE '/_%' escape '/'

/

-------------------------------------------------------------------

To generate user creation sql.

This may be useful when you do schema refresh with expdp/impdp

set pagesize 0

set heading off

set long 999999999

set feedback off

set echo off

SELECT DBMS_METADATA.GET_DDL('USER', '&1') FROM DUAL;

SELECT DBMS_METADATA.GET_GRANTED_DDL('SYSTEM_GRANT','&1') FROM DUAL;

SELECT DBMS_METADATA.GET_GRANTED_DDL( 'ROLE_GRANT','&1') FROM DUAL;

SELECT 'GRANT ' || PRIVILEGE || ' ON ' || OWNER || '.' || TABLE_NAME || ' TO ' || GRANTEE

|| ';' FROM DBA_TAB_PRIVS WHERE GRANTEE = '&1';

SELECT 'ALTER USER '||USERNAME||' QUOTA UNLIMITED ON '||TABLESPACE_NAME||';'

FROM DBA_TS_QUOTAS WHERE USERNAME='&1';

-------------------------------------------------------------------

Check for long running Transactions:

prompt Current transactions open for more than 20 minutes

prompt

col runlength HEAD 'Txn Open Minutes' format 9999.99

col sid HEAD 'Session' format a13

col xid HEAD 'TransactionID' format a18

col terminal HEAD 'Terminal' format a10

col program HEAD 'Program' format a27 wrap

select t.inst_id, sid||','||serial# sid,xidusn||'.'||xidslot||'.'||xidsqn xid, (sysdate - start_date

)* 1440

runlength ,terminal,program from gv$transaction t, gv$session s where t.addr=s.taddr

and (sysdate - start_date) * 1440 > 20;

--------------------------------------------------------------------------

Labels: SQL : Useful scripts for DBA

1 comment:

1.

AnonymousFebruary 17, 2010 11:20 PM

To shows top PGA user.

select pid,spid,substr(username,1,20) "USER" ,program,PGA_USED_MEM,PGA_ALLOC_MEM,PGA_FREEABLE_MEM,PGA_MAX_MEM from v$process where pga_alloc_mem=(select max(pga_alloc_mem) from v$process where program not like '%LGWR%');

Oracle RAC Interview questions and answers

What are Oracle Clusterware processes for 10g on Unix and Linux

Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs

as the oracle user; failure of this process results in cluster restart.

Cluster Ready Services (crsd) — The crs process manages cluster resources (which

could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an

application process, and so on) based on the resource's configuration information that is

stored in the OCR. This includes start, stop, monitor and failover operations. This

process runs as the root user 

Event manager daemon (evmd) —A background process that publishes events that crs

creates.

Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O

fencing. OPROCD performs its check, stops running, and if the wake up is beyond the

expected time, then OPROCD resets the processor and reboots the node. An OPROCD

failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck

timer on Linux platforms.

RACG (racgmain, racgimon) —Extends clusterware to support Oracle-specific

requirements and complex resources. Runs server callout scripts when FAN events

occur.

What are Oracle database background processes specific to RAC

•LMS—Global Cache Service Process

•LMD—Global Enqueue Service Daemon

•LMON—Global Enqueue Service Monitor

•LCK0—Instance Enqueue Process

To ensure that each Oracle RAC database instance obtains the block that it needs to

satisfy a query or transaction, Oracle RAC instances use two processes, the Global

Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain

records of the statuses of each data file and each cached block using a Global Resource

Directory (GRD). The GRD contents are distributed across all of the active instances.

What are Oracle Clusterware Components

Voting Disk — Oracle RAC uses the voting disk to manage cluster membership by way of

a health check and arbitrates cluster ownership among the instances in case of network

failures. The voting disk must reside on shared disk.

Oracle Cluster Registry (OCR) — Maintains cluster configuration information as well as

configuration information about any cluster database within the cluster. The OCR must

reside on shared disk that is accessible by all of the nodes in your cluster

How do you troubleshoot node reboot 

Please check metalink ...

Note 265769.1 Troubleshooting CRS Reboots 

Note.559365.1 Using Diagwait as a diagnostic to get more information for diagnosing

Oracle Clusterware Node evictions.

How do you backup the OCR

There is an automatic backup mechanism for OCR. The default location is :

$ORA_CRS_HOME\cdata\"clustername"\

To display backups : 

#ocrconfig -showbackup

To restore a backup : 

#ocrconfig -restore 

With Oracle RAC 10g Release 2 or later, you can also use the export command: 

#ocrconfig -export -s online, and use -import option to restore the contents back. 

With Oracle RAC 11g Release 1, you can do a manaual backup of the OCR with the

command: 

# ocrconfig -manualbackup 

How do you backup voting disk

#dd if=voting_disk_name of=backup_file_name

How do I identify the voting disk location 

#crsctl query css votedisk

How do I identify the OCR file location 

check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform)

or

#ocrcheck

Is ssh required for normal Oracle RAC operation ? 

"ssh" are not required for normal Oracle RAC operation. However "ssh" should be

enabled for Oracle RAC and patchset installation.

What is SCAN?

Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC) 11g

Release 2 feature that provides a single name for clients to access an Oracle Database

running in a cluster. The benefit is clients using SCAN do not need to change if you add

or remove nodes in the cluster.

Click here for more details from Oracle

What is the purpose of Private Interconnect ?

Clusterware uses the private interconnect for cluster synchronization (network

heartbeat) and daemon communication between the the clustered nodes. This

communication is based on the TCP protocol.

RAC uses the interconnect for cache fusion (UDP) and inter-process communication

(TCP). Cache Fusion is the remote memory mapping of Oracle buffers, shared between

the caches of participating nodes in the cluster. 

Why do we have a Virtual IP (VIP) in Oracle RAC? 

Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP

timeout period (which can be up to 10 min) before getting an error. As a result, you

don't really have a good HA solution without using VIPs.

When a node fails, the VIP associated with it is automatically failed over to some other

node and new node re-arps the world indicating a new MAC address for the IP.

Subsequent packets sent to the VIP go to the new node, which will send error RST

packets back to the clients. This results in the clients getting errors immediately.

What do you do if you see GC CR BLOCK LOST in top 5 Timed Events in AWR

Report? 

This is most likely due to a fault in interconnect network. 

Check netstat -s 

if you see "fragments dropped" or "packet reassemblies failed" , Work with your system

administrator find the fault with network. 

How many nodes are supported in a RAC Database?

10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100

instances in a RAC database.

Srvctl cannot start instance, I get the following error PRKP-1001 CRS-0215,

however sqlplus can start it on both nodes? How do you identify the problem? 

Set the environmental variable SRVM_TRACE to true.. And start the instance with srvctl.

Now you will get detailed error stack.

what is the purpose of the ONS daemon?

The Oracle Notification Service (ONS) daemon is an daemon started by the CRS

clusterware as part of the nodeapps. There is one ons daemon started per clustered

node.

The Oracle Notification Service daemon receive a subset of published clusterware

events via the local evmd and racgimon clusterware daemons and forward those events

to application subscribers and to the local listeners.

This in order to facilitate:

a. the FAN or Fast Application Notification feature or allowing applications to respond to

database state changes. 

b. the 10gR2 Load Balancing Advisory, the feature that permit load balancing accross

different rac nodes dependent of the load on the different nodes. The rdbms MMON is

creating an advisory for distribution of work every 30seconds and forward it via

racgimon and ONS to listeners and applications.

Labels: Oracle RAC Interview questions

19 comments:

1.

oracleandffun December 6, 2011 at 3:19 AM

how many ethernet card and how many IPs in RAC ?What is the master daemon in RAC ?

Reply

Replies

1.

sudhirMay 6, 2012 at 2:08 PM

2 NIC card and 3 IPs for each node in RAC for 10g. for 11g 3 extra IPs for SCAN

Reply

2.

AnonymousDecember 29, 2011 at 11:09 PM

When did a node becomes as "MASTER NODE" ?

Reply

Replies

1.

sudhirMay 6, 2012 at 2:03 PM

The node with the lowest node number will become master node and dynamic remastering of the resources will take place.

To find out the master node for particular resource, you can query v$ges_resource for MASTER_NODE column.

To find out which is the master node, you can see ocssd.log file and search for "master node number".

2.

sudhirMay 6, 2012 at 2:05 PM

when the first master node fails in the cluster the lowest node number will become master node

Reply

3.

AnonymousDecember 29, 2011 at 11:11 PM

what is dynamic remastering ?When will the dynamic remastering happens?

Reply

Replies

1.

sudhirMay 6, 2012 at 1:58 PM

dynamic remastering is ability to move the ownership of resource from one instance to another instance in RAC. dynamic resource remastering is used to implement for resource affinity for increased performance. resource affinity optimized the system in situation where update transactions are being executed in one instance. when activity shift to another instance the resource affinity correspondingly move to another instance. If activity is not localized then resource ownership is hashed to the instance.

In 10g dynamic remastering happens in file+object level.the process of remastering is very stringent.for one instance should touch more than 50 times than the other instance in particular period(say 10 mints). this touch ratio and time can be tuned by gc_affinity_limit and _gc_affinity_time parameter.

Reply

4.

Rahman January 3, 2012 at 6:43 AM

good questions and post in depth

Reply

5.

rameshJanuary 17, 2012 at 7:44 PM

why we maintaning odd number of voting disks?

Reply

Replies

1.

AnonymousMay 6, 2012 at 1:40 PM

In oracle RAC A node must be able to access more than half of the voting disks at any time. For example, if you have five voting disks configured, then a node must be able to access at least three of the voting disks at any time. If a node cannot access the minimum required number of voting disks it is evicted, or removed, from the cluster.

as 4 disks will not be any more highly available than 3 disks, 1/2 of 3 is

1.5...rounded to 2, 1/2 of 4 is 2, once we lose 2 disks, our cluster will fail with both 4 voting disks or 3 voting disks.

2.

Krishan Jaglan June 1, 2012 at 1:00 AM

Odd number of disk are to avoid split brain, When Nodes in cluster can't talk to each other they run to lock the Voting disk and whoever lock the more disk will survive, if disk number are even there are chances that node might lock 50% of disk (2 out of 4) then how to decide which node to evict. whereas when number is odd, one will be higher than other and each for cluster to evict the node with less number.Thankskrishan

3.

Amzad Khan August 20, 2012 at 10:31 PM

thank you sir

Reply

6.

Tanveer January 23, 2012 at 8:38 AM

good questions

Reply

7.

Rajkumar February 4, 2012 at 6:05 PM

A node must be able to access more than half of the voting disks at any timeFor example, if you have three voting disks configured, then a node must be able toaccess at least two of the voting disks at any time. If a node cannot access the minimum required number of voting disks it is evicted, or removed, from the cluster.

Reply

8.

Database DBA February 21, 2012 at 12:04 PM

Excellent sharing. Kindly provide us more questions and answers specially for RMAN with RAC.

Reply

9.

AnonymousJune 3, 2012 at 9:51 AM

Very Good blog and All Question--answers...

Q.1 Can You explain a bit about checkpoint and local & Remote listener ?

Q.2 regarding dbms scheduler jobs in RAC DB, i have observed that all scheduled jobs will run from one instance only. if manually run from other instance then it will run from that instance. does instance_stickness parameter has to do anything in this issue ?

Reply

Replies

1.

Sunil June 26, 2012 at 7:33 AM

In RAC Database, we usually see both Local and Remote Listeners. Remote listener will be scan listener wherein it acts as a load balancer.

Reply

10.

AnonymousJune 10, 2012 at 5:11 AM

Its really a one and only blog which talks about RAC FAQ in the entire web.

The article "When exactly during the installation process are clusterware components created?"is really very good. But its for 10g. If you update the blog with the 11gR2 would be really great

Reply

11.

AnonymousJuly 2, 2012 at 1:48 PM

ANY IDEA ON LOCK Monitoring in RAC? and Can some one explain?

RAC Load Balancing, TAF , FAN

Client Side Connect-Time Load Balance 

The client load balancing feature enables clients to randomize connection requests

among the listeners. 

This is done by client Tnsnames Parameter: LOAD_BALANCE.

The (load_balance=yes) instructs SQLNet to progress through the list of listener

addresses in the address_list section of the net service name in a random sequence.

When set to OFF, instructs SQLNet to try the addresses sequentially until one succeeds. 

Client Side Connect-Time failover 

This is done by client Tnsnames Parameter: FAILOVER

The (failover=on) enables clients to connect to another listener if the initial connection

to the first listener fails. Without connect-time failover, Oracle Net attempts a

connection with only one listener. 

Server Side Listener Connection Load Balancing.

With server-side load balancing, the listener directs a connection request to the best

instance currently providing the service.

Init parameter remote_listener should be set. When set, each instance registers with the

TNS listeners running on all nodes within the cluster. 

There are two types of server-side load balancing: 

Load Based — Server side load balancing redirects connections by default depending on

node load. This id default.

Session Based — Session based load balancing takes into account the number of

sessions connected to each node and then distributes the connections to balance the

number of sessions across the different nodes.

From 10g release 2 the service can be setup to use load balancing advisory. This mean

connections can be routed using SERVICE TIME and THROUGHPUT. Connection load

balancing means the goal of a service can be changed, to reflect the type of

connections using the service. 

Transparent Application Failover (TAF) 

Transparent Application Failover (TAF) is a feature of the Oracle Call Interface (OCI)

driver at client side. It enables the application to automatically reconnect to a database,

if the database instance to which the connection is made fails. In this case, the active

transactions roll back. 

Tnsnames Parameter: FAILOVER_MODE

e.g (failover_mode=(type=select)(method=basic)) 

Failover Mode Type can be Either SESSION or SELECT.

Session failover will have just the session to failed over to the next available node. With

SELECT, the select query will be resumed.

TAF can be configured with just server side service settings by using dbms_service

package.

Fast Connection Failover (FCF)

Fast Connection Failover is a feature of Oracle clients that have integrated with FAN HA

Events.

Oracle JDBC Implicit Connection Cache, Oracle Call Interface (OCI), and Oracle Data

Provider for .Net (ODP.Net) include fast connection failover. 

With fast connection failover, when a down event is received, cached connections

affected by the down event are immediately marked invalid and cleaned up.

Oracle Clusterware: Components installed

When exactly during the installation process are clusterware components

created? 

After fulfilling the pre-installation requirements, the basic installation steps to follow

are: 

1. Invoke the Oracle Universal Installer (OUI) 

2. Enter the different information for some components like: 

- name of the cluster 

- public and private node names 

- location for OCR and Voting Disks

- network interfaces used for RAC instances 

-etc. 

3. After the Summary screen, OUI will start copying under the $CRS_HOME (this is the

$ORACLE_HOME for Oracle Clusterware) in the local node the libraries and executables. 

- here we will have the daemons and scripts init.* created and configured properly. 

Oracle Clusterware is formed of several daemons, each one of which have a special

function inside the stack. Daemons are executed via the init.* scripts (init.cssd, init.crsd

and init.evmd). 

- note that for CRS only some client libraries are recreated, but not all the executables

(as for the RDBMS). 

4. Later the software is propagated to the rest of the nodes in the cluster and the

oraInventory is updated. 

5. The installer will ask to execute root.sh on each node. Until this step the software for

Oracle Clusterware is inside the $CRS_HOME. 

Running root.sh will create several components outside the $CRS_HOME: 

- OCR and VD will be formated.

- control files (or SCLS_SRC files ) will be created with the correct contents to start

Oracle Clusterware.

These files are used to control some aspects of Oracle Clusterware like:

- enable/disable processes from the CSSD family (Eg. oprocd, oslsvmon)

- stop the daemons (ocssd.bin, crsd.bin, etc).

- prevent Oracle Clusterware from being started when the machine boots.

- etc.

- /etc/inittab will be updated and the init process is notified.

In order to start the Oracle Clusterware daemons, the init.* scripts first need to be run.

These scripts are executed by the daemon init. To accomplish this some entries must be

created in the file /etc/inittab. 

- the different processes init.* (init.cssd, init.crsd, etc) will start the daemons (ocssd.bin,

crsd.bin, etc). When all the daemons are running then we can say that the installation

was successful 

- On 10.2 and later, running root.sh on the last node in the cluster also will create the

nodeapps (VIP, GSD and ONS). On 10.1, VIPCA is executed as part of the RAC

installation. 

6. After running root.sh on each node, we need to continue with the OUI session. After

pressing the 'OK' button OUI will include the information for the public and

cluster_interconnect interfaces. Also CVU (Cluster Verification Utility) will be executed

How to move OCR and Voting disk to new storage device?

Moving OCR

==========

You must be logged in as the root user, because root owns the OCR files. Also an

ocrmirror must be in place before trying to replace the OCR device.

Make sure there is a recent backup of the OCR file before making any changes:

ocrconfig –showbackup

If there is not a recent backup copy of the OCR file, an export can be taken for the

current OCR file. Use the following command to generate an export of the online OCR

file:

In 10.2 

# ocrconfig –export -s online

In 11g

# ocrconfig -manualbackup

The new OCR disk must be owned by root, must be in the oinstall group, and must have

permissions set to 640. Provide at least 100 MB disk space for the OCR.

On one node as root run:

# ocrconfig -replace ocr 

# ocrconfig -replace ocrmirror 

Now run ocrcheck to verify if the OCR is pointing to the new file

Moving Voting Disk

==================

Note: crsctl votedisk commands must be run as root

Shutdown the Oracle Clusterware (crsctl stop crs as root) on all nodes before making

any modification to the voting disk. Determine the current voting disk location using:

crsctl query css votedisk

Take a backup of all voting disk:

dd if=voting_disk_name of=backup_file_name

To move a Voting Disk, provide the full path including file name:

crsctl delete css votedisk –force

crsctl add css votedisk –force

After modifying the voting disk, start the Oracle Clusterware stack on all nodes

# crsctl start crs

Verify the voting disk location using 

crsctl query css votedisk

Labels: RAC : Moving OCR and Voting disk

1 comment:

1.

AnonymousOctober 26, 2012 10:56 PM

this procedure does not work for 11g

ocrconfig -replace ocrocrconfig -replace ocrmirror

are valid only for 10g

11gocrconfig -replace oldfile -replacement newfileis the right syntax

furthermore

raw devices are not supported in 11.2 for ocr and voting disks unless you migrated from 10g.

11g supports ocr and vting disks on ASM only.

HowTo Restore RAC Database to Single Instance On Another Node

Take RMAN backup of the production RAC database..

RMAN> run{

allocate channel c1 type disk format '/tmp/%U';

backup database;

backup archivelog all;

}

- Create a PFILE for the single instance database using the production RAC parameter

file

And modify the parameters %dest, control_files, log_archive_dest_1, %convert,

cluster_database_instances, cluster_database etc.. for undo_tablespace, mention any

one undo tablespace name

- Copy the backup pieces and the modified INIT.ORA file to the new host to same mount

point. 

- Use the pfile created above to STARTUP NOMOUNT the database on the new host

$ sqlplus "/ as sysdba"

SQL> startup nomount;

$ rman target / nocatalog

RMAN> restore controlfile from '/tmp/< backup piece name of controlfile auto

backup>';

RMAN> alter database mount;

- Determine the recovery point.

RMAN> list backup of archivelog all;

Check the last archive sequence for all redo threads and select the archive sequence

having LEAST "Next SCN" among them. 

- Having determined the point upto which media recovery should run, start the

restore/recovery using:

RMAN> run {

set until sequence < sequence# from above> thread < thread# >;

restore database;

recover database;

}

SQL> alter database open resetlogs;

If open database fail with error ORA-38856

then, Set the following parameter in the init.ora file:

_no_recovery_through_resetlogs=TRUE

Then open with resetlogs.

Once the database has opened, removed this hidden parameter.

- Once the database is opened successfully, you may remove the redolog groups for

redo threads of other instances.

SQL> select THREAD#, STATUS, ENABLED

2 from v$thread;

THREAD# STATUS ENABLED

---------- ------ --------

1 OPEN PUBLIC

2 CLOSED PRIVATE

SQL> select group# from v$log where THREAD#=2;

GROUP#

----------

4

5

6

SQL> alter database disable thread 2;

Database altered.

SQL> alter database clear unarchived logfile group 4; ( repeat for 4 to 6)

Database altered.

SQL> alter database drop logfile group 4; ( repeat for 4 to 6)

Database altered.

- Now you can remove the undo tablespaces of other instances.

SQL> show parameter undo;

NAME TYPE VALUE

------------------------------------ ----------- ------------------------------

undo_management string AUTO

undo_retention integer 900

undo_tablespace string UNDOTBS1

SQL> select tablespace_name from dba_tablespaces where contents='UNDO';

TABLESPACE_NAME

------------------------------

UNDOTBS1

UNDOTBS2

SQL> drop tablespace UNDOTBS2 including contents and datafiles;

Tablespace dropped.

How to export and import crs resources while migrating Oracle RAC to new server.

Below script generate svrctl add script for database, instance, service and 11G listeners

from OCR from current RAC.

Save the result of the script and run it at new RAC.

for DBNAME in $(srvctl config database)

do

# Generate DB resource

srvctl config database -d $DBNAME -a | awk -v dbname="$DBNAME" \

'BEGIN { FS=":" }

$1~/Oracle home/ || $1~/ORACLE_HOME/ {dbhome = "-o" $2}

$1~/Spfile/ || $1~/SPFILE/ {spfile = "-p" $2}

$1~/Disk Groups/ {dg = "-a" $2}

END { if (avail == "-a ") {avail = ""}; printf "%s %s %s %s %s\n", "srvctl add database -

d ", dbname, dbhome, spfile, dg }'

# Generate Instance resource

srvctl status database -d $DBNAME | awk -v dbname="$DBNAME" \

'$4~/running/ { printf "%s %s %s %s %s %s\n", "srvctl add instance -d ",dbname, " -i ",

$2 ," -n ", $7 }

$5~/running/ { printf "%s %s %s %s %s %s \n", "srvctl add instance -d ",dbname, " -i ",

$2 ," -n ", $8 }'

# Modify instance for 10G - ASM dependency

if [ $(echo $ORACLE_HOME | grep "1020" | wc -l ) -eq 1 ]

then

srvctl status database -d $DBNAME | awk -v dbname="$DBNAME" \

'$2~/1$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ,"

-s +ASM1" }

$2~/2$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ," -

s +ASM2" }

$2~/3$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ," -

s +ASM3" }

$2~/4$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ," -

s +ASM4" }'

fi

echo "srvctl start database -d $DBNAME"

# Generate Service resource

snamelist=$(srvctl status service -d $DBNAME | awk '{print $2}')

for sname in $snamelist

do

srvctl config service -d $DBNAME -s $sname| awk -v dbname="$DBNAME" -v

sname=$sname \

'BEGIN { FS=":"}

$1~/Preferred instances/ {pref = "-r" $2}

$1~/PREF/ {pref = "-r" $2; sub(/AVAIL/, "", pref) }

$1~/Available instances/ {avail = "-a" $2}

$2~/AVAIL/ {avail = "-a" $3}

$1~/Failover type/ {ft = "-e" $2}

$1~/Failover method/ {fm = "-m" $2}

$1~/Runtime Load Balancing Goal/ {g = "-B" $2}

END { if (avail == "-a ") {avail = ""}; printf "%s %s %s %s %s %s %s %s %s %s\n",

"srvctl add service -d ",dbname, "-s ", sname, pref, avail ,ft, fm,g, "-P BASIC"}'

echo "srvctl start service -d $DBNAME -s $sname"

done

done

# Listener at 11G Home. 10G listener can't ba added with srvctl.

srvctl config listener | awk \

'BEGIN { FS=":"; state = 0; }

$1~/Name/ {lname = "-l" $2; state=1};

$1~/Home/ && state == 1 {ohome = "-o" $2; state=2;}

$1~/End points/ && state == 2 {lport = "-p " $3; state=3;}

state == 3 {if (ohome != "-o ") {printf "%s %s %s %s\n", "srvctl add listener ", lname,

ohome, lport;} state=0;}'

Labels: How to export and import crs resources

2 comments:

1.

AnonymousDecember 8, 2011 12:58 AM

this script is not working 

gettting error as follows

awk: syntax error near line 1awk: bailing out near line 1awk: syntax error near line 1awk: bailing out near line 1srvctl start database -d lrntestawk: syntax error near line 1awk: bailing out near line 1

Reply

2.

AnonymousDecember 8, 2011 2:53 AM

I did the following two things in solaris & it is started working

#!/usr/bin/kshAWK=/usr/xpg4/bin/awk

and i have replaced all awk with $AWK in the script....

Backup & Recovery, RMAN 

Steps to recover the primary database's datafile using a copy of a standby database's datafile

Steps to recover the primary database's datafile using a copy of a standby

database's datafile.

This procedure will work for all file systems including raw or ASM.

Through this example we will be using datafile 12. 

1) On standby database, copy datafile from ASM to a file system:

RMAN> backup as copy datafile 12 format '/tmp/df12.dbf';

2) transfer the datafile copy from the standby to the primary host using scp.

On primary database

3) Place the datafile to recover offline.

SQL> alter database datafile 12 offline;

4) catalog this datafile copy:

RMAN> catalog datafilecopy '/tmp/df12.dbf';

5) Confirm that datafile exists:

RMAN> list copy of datafile 12;

6) Restore the datafile:

RMAN> restore datafile 12;

7) Recover the datafile:

RMAN> recover datafile 12;

8) Place the datafile online:

SQL> alter database datafile 12 online;

Steps to recover the standby database's datafile using a copy of a primary

database's datafile.

1) Backup the primary database's datafile.

RMAN> backup as copy datafile 12 format '/tmp/df12.dbf';

2) transfer the file to the standby site using an operating system utility such as scp.

3) catalog the datafile copy on the standby site.

RMAN> catalog datafilecopy '/tmp/df12.dbf';

4) stop redo apply on the physical standby database.

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;

5) on the standby site restore the datafile copy.

RMAN> restore datafile 12;

6) restart redo apply on the physical standby database.

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT

How to recover Standby database from a missing archivelog

Recovering a Standby database from a missing archivelog

A Physical Standby database relies on continuous application of archivelogs from a

Primary Database to be in synch with it. In Oracle Database versions prior to 10g in the

event of an archivelog gone missing or corrupt you had to rebuild the standby database

from scratch.

In 10g you can use an incremental backup from SCN and recover the standby using

the same to compensate for the missing archivelogs as shown below

Step 1: On the standby database check the current scn.

STDBY> set numwidth 30;

STDBY> select current_scn from v$database;

CURRENT_SCN

-----------

123456789

Step 2: On the primary database create the needed incremental backup from the above

SCN

C:\Documents and Settings\frego>rman target /

RMAN> {

allocate channel c1 type disk; 

BACKUP INCREMENTAL FROM SCN 123456789 DATABASE

FORMAT /tmp/incr_bkp/incr_bkp_%U';

}

Step 3: Cancel managed recovery at the standby database

STDBY>alter database recover managed standby database cancel;

Media recovery complete.

scp the backup files to standby server to /tmp/incr_bkp folder.

Step 4: Catalog the Incremental Backup Files at the Standby Database

/tmp/incr_bkp > rman target /

RMAN> CATALOG START WITH '/tmp/incr_bkp/';

searching for all files that match the pattern /tmp/incr_bkp/

List of Files Unknown to the Database

=====================================

......

Do you really want to catalog the above files (enter YES or NO)? YES

cataloging files...

cataloging done

Step 5: Apply the Incremental Backup to the Standby Database

RMAN> RECOVER DATABASE NOREDO;

Step 6: Put the standby database back to managed recovery mode.

STDBY>> recover managed standby database disconnect;

Media recovery complete.

From the alert.log you will notice that the standby database is still looking for the old

log files

*************************************************

FAL[client]: Failed to request gap sequence 

GAP - thread 1 sequence ....

**************************************************

This is because the controlfile has not been updated.

Hence the standby controlfile has to be recreated

Step 7: On the primary create new standby controlfile

PRIM>alter database create standby controlfile as ‘/tmp/incr_bkp/standby01.ctl’;

System altered.

Step 8: At Standby .. Replace standby controlfile at all location as shown by

controle_files parameter.

Copy the standby control file to the standby site. Shutdown the stanby database and

replace the stanby controlfiles and restart the standby database in managed recovery

mode...

Note: - FOR STANDBY DATABASES ON ASM additional steps is required after replacing

the stanby control file. Like renaming datafiles ...

RMAN DUPLICATE WITHOUT CONNECTING TO TARGET DATABASE IN 11GR2

Prior versions of Oracle required a connection to the TARGET and optional rman catalog

for duplicate database. 

In 11GR2, we can perform RMAN duplicate database to a new server without connecting

to the target database or a recovery catalog.

Steps.

1) Take backup of the database.

RMAN> Configure controlfile autobackup on;

RMAN> backup database plus archivelog;

2) Copy the backupsets to auxilliary server. ( In this example to /orabackup directory)

3) Create an init.ora for duplicate database.

4) Start auxilliary instance

$ export ORACLE_SID=NEWDB

$ sqlplus "/ as sysdba"

SQL> startup nomount;

5) Start rman and connect to auxiliary instance

rman auxiliary /

RMAN> DUPLICATE DATABASE TO NEWDB BACKUP LOCATION '/orabackup/'

NOFILENAMECHECK

Labels: 11GR2 : backup-based duplication

1 comment:

1.

AnonymousJuly 10, 2012 11:13 PM

I have used the sme steps but endedup with RMAN-05579:CONTROLFILE backup not found....Eventhough I have shipped the backup of the contolfile to the specified location.

Oracle 11g new features

Oracle Database 11g: New Features in DataGuard

Active Data Guard

In Oracle Database 10g and below you could open the physical standby database for

read-only activities, but only after stopping the recovery process. 

In Oracle 11g, you can query the physical standby database in real time while applying

the archived logs. This means standby continue to be in sync with primary but can use

the standby for reporting. 

Let us see the steps now..

First, cancel the managed standby recovery:

SQL> alter database recover managed standby database cancel;

Database altered.

Then, open the database as read only: 

SQL> alter database open read only;

Database altered.

While the standby database is open in read-only mode, you can resume the managed

recovery process. 

SQL> alter database recover managed standby database disconnect;

Database altered.

Snapshot Standby

In Oracle Database 11g, physical standby database can be temporarily converted into

an updateable one called Snapshot Standby Database.

In that mode, you can make changes to database. Once the test is complete, you can

rollback the changes made for testing and convert the database into a standby

undergoing the normal recovery. This is accomplished by creating a restore point in the

database, using the Flashback database feature to flashback to that point and undo all

the changes.

Steps:

Configure the flash recovery area, if it is not already done.

SQL> alter system set db_recovery_file_dest_size = 2G;

System altered.

SQL> alter system set db_recovery_file_dest= '+FRADG';

System altered.

Stop the recovery. 

SQL> alter database recover managed standby database cancel;

Database altered.

Convert this standby database to snapshot standby using command

SQL> alter database convert to snapshot standby;

Database altered.

Now recycle the database

SQL> shutdown immediate

...

SQL> startup

ORACLE instance started.

Database is now open for read/write operations

SQL> select open_mode, database_role from v$database;

OPEN_MODE DATABASE_ROLE

---------- ----------------

READ WRITE SNAPSHOT STANDBY

After your testing is completed, you would want to convert the snapshot standby

database back to a regular physical standby database by following the steps below

SQL> connect / as sysdba

Connected. 

SQL> shutdown immediate

SQL> startup mount

...

Database mounted.

SQL> alter database convert to physical standby; 

Database altered.

Now shutdown, mount the database and start managed recovery. 

SQL> shutdown

ORACLE instance shut down.

SQL> startup mount

ORACLE instance started.

...

Database mounted.

Start the managed recovery process

SQL> alter database recover managed standby database disconnect;

Now the standby database is back in managed recovery mode. When the database was

in snapshot standby mode, the archived logs from primary were not applied to it. They

will be applied now.

In 10g this can be done by following steps .. DR failover test with flashback

Redo Compression

In Oracle Database 11g you can compress the redo that goes across to the standby

server via SQL*Net using a parameter compression set to true. This works only for the

logs shipped during the gap resolution. Here is the command you can use to enable

compression.

alter system set log_archive_dest_2 = 'service=STDBYDB LGWR ASYNC 

valid_for=(ONLINE_LOGFILES,PRIMARY_ROLE) db_unique_name=STDBYDB

compression=enable'

Oracle Database 11g: New Features in RMAN

Oracle Database 11g New Features in RMAN for DBA interview.

Advice on recovery

To find out failure...

RMAN> list failure;

To get the advice on recovery

RMAN> advise failure;

Recovery Advisor generates a script that can be used to repair the datafile or resolve

the issue. The script does all the work.

To verify what the script actually does ...

RMAN> repair failure preview;

Now execute the actual repair by issuing...

RMAN> repair failure;

Proactive Health Checks

In Oracle Database 11g, a new command in RMAN, VALIDATE DATABASE, can check

database blocks for physical corruption.

RMAN> validate database;

Parallel backup of the same datafile.

In 10g each datafile is backed by only one channel. In Oracle Database 11g RMAN, the

multiple channels can backup one datafiles parallel by breaking the datafile into chunks

known as "sections." 

Optimized backup of undo tablespace.

In 10g, when the RMAN backup runs, it backs up all the data from the undo tablespace.

But during recovery, the undo data related to committed transactions are no longer

needed.

In Oracle Database 11g, RMAN bypasses backing up the committed undo data that is

not required in recovery. The uncommitted undo data that is important for recovery is

backed up as usual. This reduces the size and time of the backup.

Improved Block Media Recovery Performance

If flashback logs are present, RMAN will use these in preference to backups during block

media recovery (BMR), which can significantly improve BMR speed.

Block Change Tracking Support for Standby Databases

Block change tracking is now supported on physical standby databases, which in turn

means fast incremental backups are now possible on standby databases.

Faster Backup Compression

RMAN now supports the ZLIB binary compression algorithm as part of the Oracle

Advanced Compression option. The ZLIB algorithm is optimized for CPU efficiency, but

produces larger zip files than the BZIP2 algorithm available previously, which is

optimized for compression.

Archived Log Deletion Policy Enhancements

The archived log deletion policy of Oracle 11g has been extended to give greater

flexibility and protection in a Data Guard environment. The Oracle 10g and Oracle 11g

syntax is displayed below.

# Oracle 10g Syntax.

CONFIGURE ARCHIVELOG DELETION POLICY {CLEAR | TO {APPLIED ON STANDBY |

NONE}}

# Oracle 11g Syntax.

ARCHIVELOG DELETION POLICY {CLEAR | TO {APPLIED ON [ALL] STANDBY |BACKED UP

integer TIMES TO DEVICE TYPE deviceSpecifier |NONE | SHIPPED TO [ALL] STANDBY}

[ {APPLIED ON [ALL] STANDBY | BACKED UP integer TIMES TO DEVICE TYPE

deviceSpecifier |NONE | SHIPPED TO [ALL] STANDBY}]...}

The extended syntax allows for configurations where logs are eligible for deletion only

after being applied to, or transferred to, one or more standby database destinations.

Labels: 11g: New Features in RMAN

1 comment:

1.

Adam Gorge November 28, 2012 at 3:10 AM

One day my Oracle database get corrupted. I used RMAN Option to repair my corrupt Oracle database. But it got failed to repair my database. My friend has suggested me to try Oracle Database Recovery Software. The software is specially designed to repair corrupt Oracle Database & Files. I tried Stellar Phoenix Oracle Database Recovery Software. The software repairs database in few easy clicks. Thanks Stellar to get back my database!!

Oracle Database 11g: Invisible Indexes

Oracle 11g allows indexes to be marked as invisible. 

Invisible indexes are maintained like any other index, but they are ignored by the

optimizer unless the OPTIMIZER_USE_INVISIBLE_INDEXES parameter is set to TRUE at

the instance or session level. Indexes can be created as invisible by using the INVISIBLE

keyword, and their visibility can be toggled using the ALTER INDEX command.

CREATE INDEX index_name ON table_name(column_name) INVISIBLE;

ALTER INDEX index_name INVISIBLE;

ALTER INDEX index_name VISIBLE;

Invisible indexes can be useful for processes with specific indexing needs, where the

presence of the indexes may adversely affect other functional areas. They are also

useful for testing the impact of dropping an index.

The current visibility status of an index is indicated by the VISIBILITY column of the

[DBA|ALL|USER]_INDEXES views.

Oracle Database 11g: New Features for Automatic Memory Management

Oracle simplified memory management over the last few versions of the database.

Oracle 9i automated PGA management by introducing PGA_AGGREGATE_TARGET

parameter. Oracle 10g continued this trend by automating SGA management using the

SGA_TARGET parameter. Oracle 11g takes this one step further by allowing you to

allocate one chunk of memory, which Oracle uses to dynamically manage both the SGA

and PGA.

Automatic memory management is configured using two new initialization parameters:

•MEMORY_TARGET: The amount of shared memory available for Oracle to use when

dynamically controlling the SGA and PGA. This parameter is dynamic, so the total

amount of memory available to Oracle can be increased or decreased, provided it does

not exceed the MEMORY_MAX_TARGET limit. The default value is "0".

•MEMORY_MAX_TARGET: This defines the maximum size the MEMORY_TARGET can

be increased to without an instance restart. If the MEMORY_MAX_TARGET is not

specified, it defaults to MEMORY_TARGET setting.

When using automatic memory management, the SGA_TARGET and

PGA_AGGREGATE_TARGET act as minimum size settings for their respective memory

areas. To allow Oracle to take full control of the memory management, these

parameters should be set to zero.

Oracle Database 11g: New Features in datapump

COMPRESSION parameter in expdp

One of the big issues with Data Pump was that the dumpfile couldn't be compressed

while getting created. In Oracle Database 11g, Data Pump can compress the dumpfiles

while creating them by using parameter COMPRESSION in the expdp command line. The

parameter has three options: 

METDATA_ONLY - only the metadata is compressed

DATA_ONLY - only the data is compressed; the metadata is left alone. 

ALL - both the metadata and data are compressed. 

NONE - this is the default; no compression is performed. 

Encryption

The dumpfile can be encrypted while getting created. The encryption uses the same

technology as TDE (Transparent Data Encryption) and uses the wallet to store the

master key. This encryption occurs on the entire dumpfile, not just on the encrypted

columns as it was in the case of Oracle Database 10g. 

Data Masking 

when you import data from production to QA, you may want to make sure sensitive data

are altered in such a way that they are not identifiable. Data Pump in Oracle Database

11g enables you do that by creating a masking function and then using that during

import.

REMAP_TABLE

Allows you to rename tables during an import operation. 

  

Example

The following is an example of using the REMAP_TABLE parameter to rename the

employees table to a new name of emps:

impdp hr DIRECTORY=dpump_dir1 DUMPFILE=expschema.dmp TABLES=hr.employees

REMAP_TABLE=hr.employees:emps

Oracle Database 11g: Read only tables

Read-Only Tables in Oracle Database 11g 

Oracle 11g allows tables to be marked as read-only using the ALTER TABLE command.

ALTER TABLE table_name READ ONLY;

ALTER TABLE table_name READ WRITE;

Any DML statements that affect the table data and SELECT ... FOR UPDATE queries

result in an ORA-12081 error message.

Data Guard 

Data Guard failover with flashback

Steps for dataguard failover test with database flashback.

On Primary

Defer the log shipping to standby.

SQL> Alter system set log_archive_dest_state_n=defer;

Check last log sequence Select max(sequence#) from v$log_history

On Satndby

Enable flashback recovery.

Setup flashback destination and file size.

SQL> Alter system set db_recovery_file_dest=’/u01/flash’ scope=spfile;

SQL> Alter system set db_recovery_file_dest_size=10G scope=spfile;

Cancel the recovery.

SQL> Alter database recover managed standby database cancel;

SQL> Shutdown immediate

Startup database in mount mode.

SQL> Startup mount

Put database in the flashback mode 

SQL> alter database flashback on;

Create the Restore Point on the standby database 

SQL> Create restore point before_dr guarantee flashback database;

Activate Standby database

SQL> Alter database activate standby database;

Open the DR database

SQL> Alter database open;

Shutdown and restart the database

--- Perform DR tests --- 

Steps to rollback and convert to standby.

On Satndby

Shutdown after DR test 

SQL>Shutdown immediate

Startup database with mount and force option.

SQL>startup mount force

Restore database to the restored point. 

SQL> Flashback database to restore point before_dr;

Drop restored point 

SQL> Drop restore point before_dr;

Turn off flashback

alter database flashback off;

Convert database to physical standby 

SQL> Alter database convert to physical standby;

shutdown and startup in standby mode 

SQL> Shutdown immediate

SQL> startup nomount

SQL> Alter database mount standby database;

SQL> Alter database recover managed standby database disconnect from session;

On Production

Enable the log shipping to standby.

SQL> Alter system set log_archive_dest_state_4='enable';

switch logg and verify the apply.

SQL> alter system switch logfile;

Server Utilities ..exp/imp , expdp , impdp, SQL*Loader ... 

How to change the table name during import?

In 11g you can do this by using REMAP_TABLE

Following is the information from Oracle 11g documentation.

REMAP_TABLE

Default: There is no default

Purpose:

Allows you to rename tables during an import operation performed with the

transportable method.

Syntax and Description

REMAP_TABLE=[schema.]old_tablename[.partition]:new_tablename

You can use the REMAP_TABLE parameter to rename entire tables.

You can also use it to override the automatic naming of table partitions that were

exported using the transportable method. When partitioned tables are exported using

the transportable method, each partition and subpartition is promoted to its own table

and by default the table is named by combining the table and partition name (that is,

tablename_partitionname). You can use REMAP_TABLE to specify a name other than the

default.

Restrictions

•Only objects created by the Import will be remapped. In particular, preexisting tables

will not be remapped if TABLE_EXISTS_ACTION is set to TRUNCATE or APPEND.

Example

The following is an example of using the REMAP_TABLE parameter to rename the

employees table to a new name of emps:

impdp hr DIRECTORY=dpump_dir1 DUMPFILE=expschema.dmp

TABLES=hr.employees REMAP_TABLE=hr.employees:emps