Segment Shrink

Does anyone know if using the alter table SHRINK SPACE COMPACT will have any negative impact to the indexes? From what I have read, this will cause Oracle to re-assign the rowids to the table.

A couple of points:
1. The name of this forum is "Advanced Compression" and your question has nothing to do with the topic.
2. You didn't post a version number (3 decimal places).
3. You didn't post any DDL for the table, the indexes, or the shrink statement.
4. You didn't define what you mean by "negative impact" in terms of whatever your topic actually is.
I would suggest you repost this in the correct group "General Database" and when you do so include sufficient information that someone can help you.

Similar Messages

Segment Shrink Space Compact option in Oracle 10g

Dear All,
1. Is it Compulsory to run the Segment Shrinking Jobs advised by Segment Advisor?
2. Running online will it affect the perfomance
3. Is this same as table re organization
Thanks in Advance

1. NO. As with any "Advisor" it is your discretion and decision as to what action to take and when. I would schedule shrinks / rebuilds / reorgs during/without maintenance/outages. But first, I would evaluate the advice. In many cases, it wouldn't be worth the effort to rebuild/shrink. Also, you have to consider that the table/index may/will grow again.
I do a shrink/rebuild only as part of any archival job which deletes a significant portion of the data. Not otherwise.
2. Running it online will impact performance. Furthermore, the SHRINK actually generates a lot of Undo (as it runs as if it is normal DML) and, consequently, Redo and ArchiveLog.
3. It is different. However, the "it" also depends on what you mean to be a "table reorganization". A reorganization that is done with an ALTER TABLE MOVE (and ALTER INDEX REBUILD) is quite a different operation from a SHRINK. A DBMS_REDEFINITION is also a very different operation.

Segment shrinking and UNDO tablespace

When i issued
alter table <table_name> shrink space cascade;
I got the error 'Unable to extend UNDO ...by 8' . Does Segment shrinking consume space from UNDO tablespace?
Message was edited by:
for_good_reason

As Jonathan said, shrinking segment generates redo and undo data.
But, this phoenomenon of undo shortage is not normal case.
Shrinking segment might invole continous DML(deleting and re-inserting),
but it's transaction seems to be committed internally at regular intervals.
For this reason, shrinking operation should not hold undo area that long.
But have no knowledge on exact behavior of shrink operation.
Someone else will shed a light.
How big your table and indexes?
Some cases are reorted that shrinkage on big segment generates really large amount of undo data.
This might be related with your problem. But not sure.
Visit metalink note# 3888229.

Why Segment shrink is not supported for tables with function-based indexes

As we all know , Segment shrink is not supported for tables with function-based indexes.
But i'm very confused .
Why Segment shrink is not supported for tables with function-based indexes ?? what's its essential?

Creating a function based index creates a hidden virtual column (you'll see it if you query user_tab_cols) and once you index a virtual column you can no longer shrink the table:orcl> create table t1(c1 number,c2 as (c1 * 2)) segment creation immediate;
Table created.
orcl> alter table t1 enable row movement;
Table altered.
orcl>
orcl> alter table t1 shrink space;
Table altered.
orcl> create index i2 on t1(c2);
Index created.
orcl> alter table t1 shrink space;
alter table t1 shrink space
ERROR at line 1:
ORA-10631: SHRINK clause should not be specified for this object
orcl>so the issue is not with function based indexes per se, it is a level beneath that. Perhaps because the virtual column has no physical existance, when the row is moved there is no reason for Oracle to realize that an index needs updating? I haven't attempted to reverse engineer this, I would be interested to know if anyone else has.

Segment shrinking, any influence on performance?

Hi all
I am using 10.2.0.2 64-bit on SLES 10. I am thinking of performing segment shrinking on production database. I did it on the test database and it was time and resource consuming process. Does segment shrinking has any influence on performance apart from gain in disk space? If yes, what?
Thanks for any suggestions.
Groxy

Groxy,
As others have mentioned already, with the defragmentation of the object with the shrink command, there would be surely the increase both in the space as well as in the complete scans of the object. But I would also like to point that doing this in a live system can be degrading the performance as well by marking the cursors in the shared pool invalid. So for this, if you are considering this , better would be to use it with the compact option and than later on doing the complete shrinking.
Just my 2 cents.
Aman....

Segment Shrinking script erroring out due to Function based indexes, lobs,.

DB version:10gR2
Following is a script i made for freeing up(SHRINK ing and resetting HWM) the space in Tables and its indexes. Due to the existence of LOB Segments and Tables with Function based indexes, this script was erroring out. So i was wondering if there is a way to find out the segments which are eligible/not eligible for Shrinking so that i could make necessary changes to the below script.
create or replace procedure freeup_space
is
type v_segment_type is table of varchar2(30) index by binary_integer;
v_segment v_segment_type;
begin
select segment_name bulk collect into v_segment
               from user_segments
               where segment_type in ('TABLE')
                 and segment_name not like 'BIN%';
for i in v_segment.first..v_segment.last loop
execute immediate 'alter table ' || v_segment(i) ||' enable row movement';
dbms_output.put_line('Table '||v_segment(i)||'''s row movement enabled');
execute immediate 'alter table ' || v_segment(i) ||' shrink space cascade';
execute immediate 'alter table ' || v_segment(i) ||' deallocate unused';
end loop;
end;
/

You can use USER_LOBS views to look for LOB columns in the segments and ALL_INDEXES.INDEX_TYPE tells if the index is function based index or not.
Message was edited by:
Pierre Forstmann

Database Control and Segment Shrink

Page 10-16 of oracle10g new features for administrators
Book says to click the TABLES link in the STORAGE section.
Should that be from SCHEMA section? STORAGE section has tablespace information and not table info
Thanks,
Viji

ahb72 wrote:
Hi,
I installed Oracle 10g DB and configure its DB Control. Then, I added that database as a target to OEM Grid Control.
My question is: After adding the database as a target to the Grid control, will it be still monitored by both the DB Control and the Enterprise Grid control?I think , Yes ...
Just keep the dbconsole services down.
So stop the dbconsole and start OEM agent and monitor it from grid.
Regards
Rajesh

Error while shrinking a table

Hi All,
I am facing issue while shrinking a table PARAMETER_DETAIL which is a IOT partition table.
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.2.0 - 64bi
PL/SQL Release 10.2.0.2.0 - Production
CORE 10.2.0.2.0 Production
TNS for Solaris: Version 10.2.0.2.0 - Production
NLSRTL Version 10.2.0.2.0 - Production
SunOS usa0300ux636 5.10 Generic_138888-03 sun4v sparc SUNW,Sun-Blade-T6320
When i am firing the below query,
alter table PARAMETER_DETAIL SHRINK space CASCADE;
alter table PARAMETER_DETAIL SHRINK space CASCADE*
ERROR at line 1:
ORA-10635: Invalid segment or tablespace type
I am getting this error.
Moreover, I have checked in dba_segments, the output is
SQL> l
1 select unique SEGMENT_NAME,PARTITION_NAME,SEGMENT_TYPE,TABLESPACE_NAME from dba_segments where SEGMENT_NAME='PARAMETER_DETAIL'
2* and OWNER='CDE'
SEGMENT_NAME
PARTITION_NAME SEGMENT_TYPE TABLESPACE_NAME
PARAMETER_DETAIL
PD_201107220130 INDEX PARTITION DATAFEED
PARAMETER_DETAIL
PD_201107211630 INDEX PARTITION DATAFEED
PARAMETER_DETAIL
PD_201107212030 INDEX PARTITION DATAFEED
SEGMENT_NAME
PARTITION_NAME SEGMENT_TYPE TABLESPACE_NAME
PARAMETER_DETAIL
PD_201107212100 INDEX PARTITION DATAFEED
PARAMETER_DETAIL
PD_201107210330 INDEX PARTITION DATAFEED
PARAMETER_DETAIL
PD_201107210630 INDEX PARTITION DATAFEED
SEGMENT_NAME
PARTITION_NAME SEGMENT_TYPE TABLESPACE_NAME
PARAMETER_DETAIL
PD_201107210830 INDEX PARTITION DATAFEED
PARAMETER_DETAIL
PD_201107211030 INDEX PARTITION DATAFEED
1490 rows selected.
SQL> select TABLESPACE_NAME,SEGMENT_SPACE_MANAGEMENT from dba_tablespaces;
TABLESPACE_NAME SEGMEN
SYSTEM MANUAL
UNDOTBS MANUAL
SYSAUX AUTO
TEMP MANUAL
USERS AUTO
DATAFEED AUTO
6 rows selected.
Please help me out to shrink this table.
Thanks

http://download.oracle.com/docs/cd/B19306_01/server.102/b14231/schema.htm#ADMIN10161
Shrink operations can be performed only on segments in locally managed tablespaces with automatic segment space management (ASSM). Within an ASSM tablespace, all segment types are eligible for online segment shrink except these:
IOT mapping tables
Tables with rowid based materialized views
Tables with function-based indexesSince this is an IOT, any chance there is an IOT mapping table?
Since this appears to be a data warehouse, any chance there are ROWID based materialized views or function-based indexes?
Justin

Seqment shrink with function based indexes - 10.2.0.3

I see 10g Rel 2 limiation with function based index while doing segment shrink. Is their a workaround? I tried to drop the function based index before shrink, still shrink is taking several hrs to complete.
Any help is appreciated.
Thanks,
Siva

Hi,
Analogy: suppose you have 1 million barrels filled with water near 85% maybe less, now you spilled ...say 40% the total water, maybe you have 400,000 empty barrels or the equivalent (here comes the overhead) you are going to concentrate the water in 600,000 barrels and return the empty ones to the "Oracle Server" store, just to reclaim them gradually until you have the starting 1 million barrel.
Our advise: keep the objects as they are, both table and index. Oracle will use released space as efficiently as he can, which is (at that level) better than us.
You're worried about the index space? much better leave it now, that's the structure which may cause the major part of overhead.
Regards
Ignacio
http://oracledisect.blogspot.com

Segment space for Manual tablespace management

Hi,
wanted to know if 10g segment advisor can advise on segments that exsists in a tablespaces that is set to manual extent management.
thanks,
Ven.

From the
Oracle® Database Administrator's Guide
10g Release 2 (10.2)
Part Number B14231-01
14 Managing Space for Schema Objects
Understanding Reclaimable Unused Space
You use the Segment Advisor to identify segments that would benefit from online segment shrink. Only segments in locally managed tablespaces with automatic segment space management (ASSM) are eligible. Other restrictions on segment type exist. For more information, see "Shrinking Database Segments Online".

Alter table modify lob shrink space hangs despite ddl_lock_timeout

Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production
The following command hangs despite session parameter ddl_lock_timeout being set to 0:
alter table <table> modify lob (<column>) (shrink space);
Data type of <column> is CLOB. In another session a transaction on <table> is open, with a simple update on a different (non-LOB) column.
Looks like a bug to me, but have no access to metalink for confirmation/SR submission and would appreciate any comments/help on this issue.

From Oracle 11 documentation ( http://docs.oracle.com/cd/B28359_01/server.111/b28310/schema003.htm#CBBBIADA )
"Segment shrink is an online, in-place operation. DML operations and queries can be issued during the data movement phase of segment shrink."
Simon

Anyway to shrink tablespace online?

I have a 500GB tablespace with 10 files, that was full, after deleting, purge, it is half free now, I want to reduce datafile size, but I can not do "alter database datafile resize...." as some object in the end of the file.
anyway to shrink tablespace/datafiles online?
Thanks!!

Oh, sorry I thought they pointed you in the right direction.
What about using the SHRINK SPACE command? Take a look at it here...
http://download.oracle.com/docs/cd/B28359_01/server.111/b28310/schema003.htm#ADMIN10161
It seems to do what you want.
You use online segment shrink to reclaim fragmented free space below the high water mark in an Oracle Database segment. The benefits of segment shrink are these:
Compaction of data leads to better cache utilization, which in turn leads to better online transaction processing (OLTP) performance.
The compacted data requires fewer blocks to be scanned in full table scans, which in turns leads to better decision support system (DSS) performance.
Segment shrink is an online, in-place operation. DML operations and queries can be issued during the data movement phase of segment shrink. Concurrent DML operation are blocked for a short time at the end of the shrink operation, when the space is deallocated. Indexes are maintained during the shrink operation and remain usable after the operation is complete. Segment shrink does not require extra disk space to be allocated.
Segment shrink reclaims unused space both above and below the high water mark. In contrast, space deallocation reclaims unused space only above the high water mark. In shrink operations, by default, the database compacts the segment, adjusts the high water mark, and releases the reclaimed space.
Segment shrink requires that rows be moved to new locations. Therefore, you must first enable row movement in the object you want to shrink and disable any rowid-based triggers defined on the object. You enable row movement in a table with the ALTER TABLE ... ENABLE ROW MOVEMENT command.

Shrinking Tables

In 10g, the Segment Advisor recommended the shrinking of one of my tables. Since it was a test DB, I implemented the recommendation.
Unforunately, the script failed and I received ORA-10631: SHRINK clause should not be specified for this object. I've done some reseach on the issue and found that not enabling row movement on a table can cause the error.
I checked my table and row movement IS enabled. I was wondering if anyone could tell me what else could be causing the problem.
Jim

I was wondering if anyone could tell me what else could be causing the problem.SHRINK option has some restrictions. From Oracle documentation :
Restrictions on the shrink_clause The shrink_clause is subject to the following restrictions:
* You cannot specify this clause for a cluster, a clustered table, or any object with a LONG column.
* Segment shrink is not supported for tables with function-based indexes or bitmap join indexes.
* This clause does not shrink mapping tables of index-organized tables, even if you specify CASCADE.
* You cannot specify this clause for a compressed table.
* You cannot shrink a table that is the master table of an ON COMMIT materialized view. Rowid materialized views must be rebuilt after the shrink operation.

Shrinking BLOB

I am in 10.2.0.3.
I have a huge LOB segement - 120G associated with a BLOB column in one of my tables. After running empty_blob I need to shrink space using:
alter table mytable modify lob (mylobcolumn) (shrink space);.
This command ran for 9 hrs and had to be stopped because of time constraints.
I ran a test on 0.5G bolb and shrinking space took only 80 sec, which (under linear extrapolation) should give 5-6 hrs for 120G to shrink.
Questions from anynoe with relevant experience:
- Is this a good estimate (based on my little test)?
- Any other way to recliam space from empty blob?
- Can I ran application which maybe using this table with a blob (I mean during shrink command not during empty_blob)?
Thanks in advance!

Among other factors, a lot is going to depend on how expensive moving the data around is going to be. Online segment shrinking relies on moving rows around physically within the table, so a linear extrapolation based solely on the size of the LOB segment probably isn't particularly accurate.
If you literally assigned every LOB in the table to EMPTY_BLOB, it would probably be quicker to move the (essentially empty) LOB segment from the existing tablespace to a new tablespace (and possibly back) during a downtime window. If there is still a lot of data in the LOB segment, you can do a COMPACT, rather than SHRINK SPACE, which can run while the application is online and then later do the SHRINK SPACE (which should be very quick since the COMPACT had already done the vast majority of the work). At the very end, SHRINK SPACE does have to lock the table, but generally it only has to do so briefly.
Justin

Oracle 10G New Feature........Part 1

Dear all,
from last couple of days i was very busy with my oracle 10g box,so i think this is right time to
share some intresting feature on 10g and some internal stuff with all of you.
Have a look :-
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Oracle 10g Memory and Storage Feature.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1.Automatic Memory Management.
2.Online Segment Shrink
3.Redolog Advisor, checkpointing
4.Multiple Temporary tablespace.
5.Automatic Workload Repository
6.Active Session History
7.Misc
a)Rename Tablespace
b)Bigfile tablespace
c)flushing buffer cache
8.ORACLE INTERNAL
a)undocumented parameter (_log_blocks_during_backup)
b)X$ view (x$messages view)
c)Internal Structure of Controlfile
1.Automatic memory management
================================
This feature reduce the overhead of oracle DBA.previously mostly time we need to set diff oracle SGA parameter for
better performance with the help of own experience,advice views and by monitoring the behaviour
of oracle database.
this was just time consuming activity.........
Now this feature makes easy life for oracle DBA.
Just set SGA_TARGET parameter and it automatically allocate memory to different SGA parameter.
it focus on DB_CACHE_SIZE
SHARED_POOL_SIZE
LARGE_POOL
JAVA_POOL
and automatically set it as
__db_cache_size
__shared_pool_size
__large_pool_size
__java_pool_size
check it in alert_log
MMAN(memory manager) process is new in 10g and this is responsible for sga tuning task.
it automatically increase and decrease the SGA parameters value as per the requirement.
Benefit:- Maximum utlization of available SGA memory.
2.Online Segment Shrink.
==========================
hmmmmm again a new feature by oracle to reduce the downtime.Now oracle mainly focus on availablity
thats why its always try to reduce the downtime by intrducing new feature.
in previous version ,reducing High water mark of table was possible by
Exp/imp
or
alter table move....cmd. but on these method tables was not available for normal use for long hrs if it has more data.
but in 10g with just few command we can reduce the HWmark of table.
this feature is available for ASSM tablespaces.
1.alter table emp enable row movement.
2.alter table emp shrink space.
the second cmd have two phases
first phase is to compact the segment and in this phase DML operations are allowed.
second phase(shrink phase)oracle shrink the HWM of table, DML operation will be blocked at that time for short duration.
So if want to shrink the HWM of table then we should use it with two diff command
first compact the segment and then shrink it on non-peak hrs.
alter table emp shrink space compact. (This cmd doesn't block the DML operation.)
and alter table emp shrink space. (This cmd should be on non-peak hrs.)
Benefit:- better full table scan.
3.Redolog Advisor and checkpointing
================================================================
now oracle will suggest the size of redo log file by V$INSTANCE_RECOVERY
SELECT OPTIMAL_LOGFILE_SIZE
FROM V$INSTANCE_RECOVERY
this value is influence with the value of FAST_START_MTTR_TARGET .
Checkpointing
Automatic checkpointing will be enable after setting FAST_START_MTTR_TARGET to non-zero value.
4.Multiple Temporary tablespace.
==================================
Now we can manage multiple temp tablespace under one group.
we can create a tablespace group implicitly when we include the TABLESPACE GROUP clause in the CREATE TEMPORARY TABLESPACE or ALTER TABLESPACE statement and the specified tablespace group does not currently exist.
For example, if group1 is not exists,then the following statements create this groups with new tablespace
CREATE TEMPORARY TABLESPACE temp1 TEMPFILE '/u02/oracle/data/temp01.dbf'
SIZE 50M
TABLESPACE GROUP group1;
--Add Existing temp tablespace into group by
alter tablespace temp2 tablespace group group1.
--we can also assign the temp tablespace group on database level as default temp tablespace.
ALTER DATABASE <db name> DEFAULT TEMPORARY TABLESPACE group1;
benefit:- Better I/O
One sql can use more then one temp tablespace
5.AWR(Automatic Workload Repository):-
================================== AWR is built in Repository and Central point of Oracle 10g.Oracle self managing activities
is fully dependent on AWR.by default after 1 hr, oracle capure all database uses information and store in AWR with the help of
MMON process.we called it Memory monitor process.and all these information are kept upto 7 days(default) and after that it automatically purge.
we can generate a AWR report by
SQL> @?/rdbms/admin/awrrpt
Just like statspack report but its a advance and diff version of statspack,it provide more information of Database as well as OS.
it show report in Html and Text format.
we can also take manually snapshot for AWR by
BEGIN
DBMS_WORKLOAD_REPOSITORY.CREATE_SNAPSHOT ();
END;
**The STATISTICS_LEVEL initialization parameter must be set to the TYPICAL or ALL to enable the Automatic Workload Repository.
[oracle@RMSORA1 oracle]$ sqlplus / as sysdba
SQL*Plus: Release 10.1.0.2.0 - Production on Fri Mar 17 10:37:22 2006
Copyright (c) 1982, 2004, Oracle. All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.1.0.2.0 - Production
With the Partitioning, OLAP and Data Mining options
SQL> @?/rdbms/admin/awrrpt
Current Instance
~~~~~~~~~~~~~~~~
DB Id DB Name Inst Num Instance
4174002554 RMSORA 1 rmsora
Specify the Report Type
~~~~~~~~~~~~~~~~~~~~~~~
Would you like an HTML report, or a plain text report?
Enter 'html' for an HTML report, or 'text' for plain text
Defaults to 'html'
Enter value for report_type: text
Type Specified: text
Instances in this Workload Repository schema
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
DB Id Inst Num DB Name Instance Host
* 4174002554 1 RMSORA rmsora RMSORA1
Using 4174002554 for database Id
Using 1 for instance number
Specify the number of days of snapshots to choose from
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Entering the number of days (n) will result in the most recent
(n) days of snapshots being listed. Pressing <return> without
specifying a number lists all completed snapshots.
Listing the last 3 days of Completed Snapshots
Snap
Instance DB Name Snap Id Snap Started Level
rmsora RMSORA 16186 16 Mar 2006 17:33 1
16187 16 Mar 2006 18:00 1
16206 17 Mar 2006 03:30 1
16207 17 Mar 2006 04:00 1
16208 17 Mar 2006 04:30 1
16209 17 Mar 2006 05:00 1
16210 17 Mar 2006 05:31 1
16211 17 Mar 2006 06:00 1
16212 17 Mar 2006 06:30 1
16213 17 Mar 2006 07:00 1
16214 17 Mar 2006 07:30 1
16215 17 Mar 2006 08:01 1
16216 17 Mar 2006 08:30 1
16217 17 Mar 2006 09:00 1
Specify the Begin and End Snapshot Ids
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Enter value for begin_snap: 16216
Begin Snapshot Id specified: 16216
Enter value for end_snap: 16217
End Snapshot Id specified: 16217
Specify the Report Name
~~~~~~~~~~~~~~~~~~~~~~~
The default report file name is awrrpt_1_16216_16217.txt. To use this name,
press <return> to continue, otherwise enter an alternative.
Benefit:- Now DBA have more free time to play games.....................:-)
Advance version of statspack
more DB and OS information with self managing capabilty
New Automatic alert and database advisor with the help of AWR.
6.Active Session History:-
==========================
V$active_session_history is view that contain the recent session history.
the memory for ASH is comes from SGA and it can't more then 5% of Shared pool.
So we can get latest and active session report from v$active_session_history view and also get histortical data of
of session from DBA_HIST_ACTIVE_SESS_HISTORY.
v$active_session_history include some imp column like:-
~SQL identifier of SQL statement
~Object number, file number, and block number
~Wait event identifier and parameters
~Session identifier and session serial number
~Module and action name
~Client identifier of the session
7.Misc:-
========
Rename Tablespace:-
=================
in 10g,we can even rename a tablespace by
alter tablespace <tb_name> rename to <tb_name_new>;
This command will update the controlfile,data dictionary and datafile header,but dbf filename will be same.
**we can't rename system and sysaux tablespace.
Bigfile tablespace:-
====================
Bigfile tablespace contain only one datafile.
A bigfile tablespace with 8K blocks can contain a 32 terabyte datafile.
Bigfile tablespaces are supported only for locally managed tablespaces with automatic segment-space management.
we can take the advantage of bigfile tablespace when we are using ASM or other logical volume with RAID.
without ASM or RAID ,it gives poor response.
syntax:-
CREATE BIGFILE TABLESPACE bigtbs
Flushing Buffer Cache:-
======================
This option is same as flushing the shared pool,but only available with 10g.
but i don't know, whats the use of this command in prod database......
anyway we can check and try it on test server for tuning n testing some query etc....
SQL> alter system flush buffer_cache;
System altered.
++++++++++++++++++
8.Oracle Internal
++++++++++++++++++
Here is some stuff that is not related with 10g but have some intresting things.
a)undocumented parameter "_log_blocks_during_backup"
++++++++++++++++++++++++
as we know that oracle has generate more redo logs during hotbackup mode because
oracle has to maintain the a complete copy of block into redolog due to split block.
we can also change this behaviour by setting this parameter to False.
If Oracle block size equals the operating system block size.thus reducing the amount of redo generated
during a hot backup.
WITHOUT ORACLE SUPPORT DON'T SET IT ON PROD DATABASE.THIS DOCUMENT IS JUST FOR INFORMATIONAL PURPOSE.
b)some X$ views (X$messages)
++++++++++++++++
if you are intresting in oracle internal architecture then x$ view is right place for getting some intresting things.
X$messages :-it show all the actions that a background process do.
select * from x$messages;
like:-
lock memory at startup MMAN
Memory Management MMAN
Handle sga_target resize MMAN
Reset advisory pool when advisory turned ON MMAN
Complete deferred initialization of components MMAN
lock memory timeout action MMAN
tune undo retention MMNL
MMNL Periodic MQL Selector MMNL
ASH Sampler (KEWA) MMNL
MMON SWRF Raw Metrics Capture MMNL
reload failed KSPD callbacks MMON
SGA memory tuning MMON
background recovery area alert action MMON
Flashback Marker MMON
tablespace alert monitor MMON
Open/close flashback thread RVWR
RVWR IO's RVWR
kfcl instance recovery SMON
c)Internal Structure of Controlfile
++++++++++++++++++++++++++++++++++++
The contents of the current controlfile can be dumped in text form.
Dump Level Dump Contains
1 only the file header
2 just the file header, the database info record, and checkpoint progress records
3 all record types, but just the earliest and latest records for circular reuse record types
4 as above, but includes the 4 most recent records for circular reuse record types
5+ as above, but the number of circular reuse records included doubles with each level
the session must be connected AS SYSDBA
alter session set events 'immediate trace name controlf level 5';
This dump show lots of intresting information.
it also show rman recordes if we used this controlfile in rman backup.
Thanks
Kuljeet Pal Singh

You can find each doc in html and pdf format on the Documentation Library<br>
You can too download all the documentation in html format to have all on your own computer here (445.8MB)<br>
<br>
Nicolas.

Segment Shrink

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