how to enable / disable archive log mode in oracle

Friends after long time back to blog …. due to lots of up / down in life I was away from blog …. but promise from here onward will be in touch with you guys and will always reply your queries and suggestions …

Most of Jr. DBA while chating ask the question abt archive enable / disable query , so just coming with basic but most useful post for Jr.DBA.

Also please note , whenever we enabling the DB in archive mode as DBA we need to monitor the archive space as well.

In large database environmnet we need to take regular archive so backup , so generaly DBA use to schedule it to keep the free space in archive location.

Otherwise DB may go in hung state if archive location is fulled.

In oraganisation some time archive file is manually deleted by DBA it self or we schedule it to delete once it is backup.

This is how to enable archiving:
 

SQL*Plus: Release 10.2.0.4.0 – Production on Tue Feb 26 09:57:43 2013

Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.

Connected to: Oracle Database 10g Release 10.2.0.4.0 – 64bit Production
SQL> archive log list
Database log mode              No Archive Mode
Automatic archival             Disabled
Archive destination            /oracle/SID/oraarch
Oldest online log sequence     2442
Current log sequence           2444

 SQL> shutdown immediate
 Database closed.
 Database dismounted.
 ORACLE instance shut down.
 SQL> startup mount
 ORACLE instance started.
 
Total System Global Area 289406976 bytes
 Fixed Size 1248576 bytes
 Variable Size 96469696 bytes
 Database Buffers 184549376 bytes
 Redo Buffers 7139328 bytes
 Database mounted.
 SQL> alter database archivelog;
 
Database altered.
 
SQL> alter database open;
 
Database altered.
 
SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /oracle/SID/oraarch
Oldest online log sequence     26
Next log sequence to archive   28
Current log sequence           28
 SQL>
 
=================================================
 
This is how to disable archiving:
 
SQL> shutdown immediate
 Database closed.
 Database dismounted.
 ORACLE instance shut down.
 SQL> startup mount
 ORACLE instance started.
 
Total System Global Area 289406976 bytes
 Fixed Size 1248576 bytes
 Variable Size 100664000 bytes
 Database Buffers 180355072 bytes
 Redo Buffers 7139328 bytes
 Database mounted.
 SQL> alter database noarchivelog;
 
Database altered.
 
SQL> alter database open;
 
Database altered.
 
SQL> archive log list
Database log mode              No Archive Mode
Automatic archival             Disabled
Archive destination            /oracle/SID/oraarch
Oldest online log sequence     26
Current log sequence           28
SQL>

 

I Hope this article helped to you. I am expecting your suggestions/feedback.

It will help to motivate me to write more articles….!!!!

 

Thanks & Regards,

Samadhan

https://samadhandba.wordpress.com/

“Key for suceess, always fight even knowing your defeat is certain….!!!!

 

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Wait event Read by other session or Buffer busy

Dear friends,
     Today I saw AWR report Top 5 time wait events. I saw one wait event “read by other session “.
Read by other session wait event & Buffer busy wait event are same.

Oracle 9i we called buffer busy wait event and oracle 10g/later we called “read by other session”

About “Read by other session wait event”

When a user issue the query in a database, oracle server processes will read the database blocks from disk to database buffer cache. When two or more session issue the same query/related query (access the same database blocks), the first session will read the data from database buffer cache while other sessions are in wait.

The resolution of a “buffer busy wait”  events is one of the most confounding problems with Oracle.  In an I/O-bound Oracle system, buffer busy waits are common, as evidenced by any system with read (sequential/scattered) waits in the top-five waits.

We simply say, several concurrent sessions will read the same blocks/same table or same index block.

How can we find the block contention?

AWR/Statspack report top 5 wait event shows the read by other session or Buffer busy wait event and also we can see wait event section.

SELECT p1 “file#”, p2 “block#”, p3 “class#”
FROM v$session_wait
WHERE event = ‘read by other session’;

SELECT p1 “file#”, p2 “block#”, p3 “wait class#”
FROM v$session_wait
WHERE event = ‘buffer busy waits’;

Also using v$segment_statistics or v$system_event we can see the buffer busy wait event.

How can we tune the Read by other session wait event?

Hot Objects/Blocks:

Number of concurrent session’s access single block in an object is known as hot object.

Using AWR report “Segment statistics” section shows the HOT objects list.

Or using below query we find the hot objects.

SELECT relative_fno, owner, segment_name, segment_type
FROM dba_extents
WHERE file_id = &file
AND &block BETWEEN block_id AND block_id + blocks – 1;

Why buffer busy wait/read by other session event happen? How we reduce the buffer busy waits?

Increasing INITRANS value method:

First we should know how concurrent sessions accessing a single block in an object?

Each db block having 3 layers.

1. Cache layer
2. Transaction layer
3. Data layer

Transaction layer is playing vital role for block contention.

Each block will have ITL (INTERESTED TRANSACTION LIST) slots. This ITL slots is required for any sessions that’s need to modify a block in an object.

INITRANS value for table having segment 1 & INITRANS for index segment having 2.

MAXTRANS value default is 255.
If there is no free ITL slot in a blocks, then transaction will waiting for serially for a free ITL slot. By increasing INITRANS value to avoid the serial transaction waiting. Concurrently number of session will perform the DML operation in single block.
Each ITL requires approximately 23 bytes in the block header.

Increasing PCTFREE method:

Suppose a single 8 KB block contains 1000 rows. We reducing the rows in a block can easily reduce the buffer busy wait.

PCTFREE space is used for future updates only. We have an 8 KB data block. Default PCTFREE value is 10%. If we increased the PCTFREE value is 20% automatically number of rows inserted in a block is automatically reduced.

Reducing database block size method:

It’s similar to PCTFREE method. Suppose a single 8 KB block contains 1000 rows. Using db multiblock size future we used 4 KB data block. Now 1000 rows should be stored two 4 KB blocks.

Our goal is to reduce the number of records stored in a block.

Tune the inefficient queries:

Reduce the number of blocks accessing for an objects in buffer cache. By tuning the query to minimize the number of blocks reads from disk to database buffer cache.

Example: I have a one huge table & it contains 10000 blocks. There is no index for this table.If we doing any operation against this table, it’s going full table scan & accessing all the blocks in a table (server process reads the 10000 blocks from disk to database buffer cache). We can put proper index for this table & avoid the full table scan.

Conclution:

Tune inefficient queries
Review the execution plan and make sure the plan chosen by Oracle is that read the fewest blocks possible. Optimize the SQL statement to reduce the number of physical and logical reads.

Adjust PCTFREE and PCTUSED
Adjusting the PCTFREE value downward for an object will reduce the number of rows physically stored in a block. Adjusting the PCTUSED value for an object keeps that object from getting prematurely put back on the freelist. Increase the number of FREELISTS and FREELIST GROUPS. Depending on the type of contention, adjusting these values could help distribute data among more blocks and reduce the hot block problem. Be careful to optimize these parameters so blocks do move in and out of the freelist too frequently.

Reduce the Block Size
This is very similar to adjusting the PCTFREE and PCTUSED parameters in that the goal is to reduce the amount of data stored within one block. In Oracle 9i and higher this can be achieved by storing the hot object in a tablespace with a smaller block size. In databases prior to Oracle 9i the entire database must be rebuilt with a smaller block size.

Optimize indexes
A low cardinality index has a relatively small number of unique values, e.g. a column containing state data with only 50 values. Similar to inefficient queries, the use of a low cardinality index could cause excessive number of blocks to be read into the buffer cache and cause premature aging out of “good” blocks.

I Hope this article helped to you. I am expecting your suggestions/feedback.
It will help to motivate me to write more articles….!!!!

Thanks & Regards,
Samadhan
https://samadhandba.wordpress.com/
“Key for suceess, always fight even knowing your defeat is certain….!!!!”

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Tuning PGA memory in Oracle10g

Checking PGA for each sessions

You can check session level PGA using V$SESSTAT and V$SESSION view and also you can check the username, who is using that memory.

SELECT
s.value,s.sid,a.username
FROM
V$SESSTAT S, V$STATNAME N, V$SESSION A
WHERE
n.STATISTIC# = s.STATISTIC# and
name = ‘session pga memory’
AND s.sid=a.sid
ORDER BY s.value;

VALUE SID USERNAME
———- ———- ——————————
487276 1070 APPS
552812 1068 SYS
552812 1088
618348 1009 APPS_READ_ONLY
683884 1091
749420 846 MOBILEADMIN
749420 1090
749420 1051 APPLSYSPUB
749420 1000 APPLSYSPUB
749420 929 APPLSYSPUB
790412 1093

To check the total PGA in use and hit ratio for PGA

SQL> SELECT * FROM V$PGASTAT;

NAME VALUE UNIT
————————————————– ———- ————
aggregate PGA target parameter 4294967296 bytes
aggregate PGA auto target 3674290176 bytes
global memory bound 201252864 bytes
total PGA inuse 218925056 bytes
total PGA allocated 433349632 bytes
maximum PGA allocated 1526665216 bytes
total freeable PGA memory 86835200 bytes
process count 113
max processes count 250
PGA memory freed back to OS 8.3910E+10 bytes
total PGA used for auto workareas 6505472 bytes

NAME VALUE UNIT
————————————————– ———- ————
maximum PGA used for auto workareas 70296576 bytes
total PGA used for manual workareas 0 bytes
maximum PGA used for manual workareas 4292608 bytes
over allocation count 0
bytes processed 2.1553E+11 bytes
extra bytes read/written 10403840 bytes
cache hit percentage 99.99 percent
recompute count (total) 205474

19 rows selected.

The ideal way to perform sorts is by doing the entire job in memory. A sort job that Oracle performs entirely in memory is said to be an optimal sort. If you set the PGA_AGGREGATE_TARGET too low, some of the sort data is written out directly to disk (temporary tablespace) because the sorts are too large to fit in memory. If only part of a sort job spills over to disk, it’s called a 1-pass sort. If the instance performs most of the sort on disk instead of in memory, the response time will be high. This is called multi pass sort.

Another method of checking the efficiency of PGA memory is to check V$SQL_WORKAREA_HISTOGRAM.

V$SQL_WORKAREA_HISTOGRAM displays the cumulative work area execution statistics (cumulated since instance startup) for different work area groups. The work areas are split into 33 groups based on their optimal memory requirements with the requirements increasing in powers of two. That is, work areas whose optimal requirement varies from 0 KB to 1 KB, 1 KB to 2 KB, 2 KB to 4 KB, … and 2 TB to 4 TB.

For each work area group, the V$SQL_WORKAREA_HISTOGRAM view shows how many work areas in that group were able to run in optimal mode, how many were able to run in one-pass mode, and finally how many ran in multi-pass mode. The DBA can take a snapshot at the beginning and the end of a desired time interval to derive the same statistics for that interval.

SELECT
low_optimal_size/1024 “Low (K)”,
(high_optimal_size + 1)/1024 “High (K)”,
optimal_executions “Optimal”,
onepass_executions “1-Pass”,
multipasses_executions “>1 Pass”
FROM v$sql_workarea_histogram
WHERE total_executions <> 0;

Low (K) High (K) Optimal 1-Pass >1 Pass
———- ———- ———- ———- ———-
2 4 6254487 0 0
64 128 110568 0 0
128 256 20041 0 0
256 512 86399 0 0
512 1024 145082 0 0
1024 2048 31207 0 0
2048 4096 104 0 0
4096 8192 79 2 0
8192 16384 116 0 0
16384 32768 30 0 0
32768 65536 4 0 0

Low (K) High (K) Optimal 1-Pass >1 Pass
———- ———- ———- ———- ———-
65536 131072 2 0 0

12 rows selected.

You can check the proportion of work areas since you started the Oracle instance, using optimal, 1-pass, and multipass PGA memory sizes.

SELECT name PROFILE, cnt COUNT,
DECODE(total, 0, 0, ROUND(cnt*100/total)) PERCENTAGE
FROM (SELECT name, value cnt, (sum(value) over ()) total
FROM V$SYSSTAT
WHERE name like ‘workarea exec%’);

PROFILE COUNT PERCENTAGE
————————————————– ———- ———-
workarea executions – optimal 6650608 100
workarea executions – onepass 2 0
workarea executions – multipass 0 0

Since almost all the sorting and temporary operation are carried out inder optimal catagory we can conclude that out PGA is sized correctly.

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SAP BRTOOLS for table reorganization

** Tested with UNIX / Solarise operating system.

Sorry guy’s for delay on new post.As we were on trip to GOA for one week.So now we will continue with BR Tool.

So here is another one tested example for table reorganization using the BRTOOL. Hope you guys enjoy with this one as well…..!!!!

bash-3.00$ /oracle/brspace -u / -f tbreorg -t BALDAT -degree 8
BR1001I BRSPACE 7.00 (51)
BR1002I Start of BRSPACE processing: sefphmbn.tbr 2011-04-06 07.40.07
BR0484I BRSPACE log file: /oracle/P2/sapreorg/sefphmbn.tbr
BR1301W Error message from likeywlib:
===…could not load SSF library /usr/sap/SAM/SYS/exe/run/libsapsecu.so .

BR1301W Error message from likeywlib: likey_init: Tried to load SAPSECU lib (“/usr/sap/SAM/SYS/exe/run/libsapsecu.so”), rc = 10.
BR1301W Error message from likeywlib:
===…could not load SSF library libsapsecu.so .

BR1301W Error message from likeywlib: likey_init: Couldn’t load SAPSECULIB (“libsapsecu.so”) using function SsfSupInit (), rc = 10.
BR1302W Initialization of license key library likeywlib failed, return code 1
BR1304W Checking SAP license failed at location BrLicCheck-108
BR0602W No valid SAP license found – please contact SAP

BR0280I BRSPACE time stamp: 2011-04-06 07.40.14
BR1009I Name of database instance: SAM

BR1010I BRSPACE action ID: sefphmbn
BR1011I BRSPACE function ID: tbr
BR1012I BRSPACE function: tbreorg

BR0280I BRSPACE time stamp: 2011-04-06 07.40.22
BR0657I Input menu 353 – please enter/check input values
——————————————————————————-
Options for reorganization of tables: SAPSR3.BALDAT (degree 1)

 1 ~ New destination tablespace (newts) …….. []
 2 ~ Separate index tablespace (indts) ……… []
 3 – Parallel threads (parallel) …………… [1]
 4 ~ Table/index parallel degree (degree) …… [8]
 5 – Create DDL statements (ddl) …………… [yes]
 6 ~ Category of initial extent size (initial) . []
 7 ~ Sort by fields of index (sortind) ……… []
 8 – Table reorganization mode (mode) ………. [online]

Standard keys: c – cont, b – back, s – stop, r – refr, h – help
——————————————————————————-
BR0662I Enter your choice:
c
BR0280I BRSPACE time stamp: 2011-04-06 07.40.39
BR0663I Your choice: ‘c’
BR0259I Program execution will be continued…

BR0280I BRSPACE time stamp: 2011-04-06 07.40.39
BR1108I Checking tables for reorganization…

BR0280I BRSPACE time stamp: 2011-04-06 07.40.40
BR1112I Number of tables selected/skipped for reorganization: 1/0

BR0280I BRSPACE time stamp: 2011-04-06 07.40.41
BR0370I Directory /oracle/SAM/sapreorg/sefphmbn created

BR0280I BRSPACE time stamp: 2011-04-06 07.40.41
BR1101I Starting online table reorganization…
BR0280I BRSPACE time stamp: 2011-04-06 07.40.42
BR1124I Starting online reorganization of table SAPSR3.BALDAT …
BR0280I BRSPACE time stamp: 2011-04-06 07.54.13
BR1105I Table SAPSR3.BALDAT reorganized successfully

BR0280I BRSPACE time stamp: 2011-04-06 07.54.13
BR1141I 1 of 1 table processed – 14230500 of 14230500 rows done
BR0204I Percentage done: 100.00%, estimated end time: 7:54
BR0001I **************************************************

BR0280I BRSPACE time stamp: 2011-04-06 07.54.13
BR1102I Number of tables reorganized successfully: 1

BR0280I BRSPACE time stamp: 2011-04-06 07.54.13
BR0670I Enter ‘c[ont]’ to continue, ‘b[ack]’ to go back, ‘s[top]’ to abort:
s
BR0280I BRSPACE time stamp: 2011-04-06 07.57.27
BR0257I Your reply: ‘s’
BR0679I Do you really want to cancel BRSPACE? Enter y[es]/n[o]:
y
BR0280I BRSPACE time stamp: 2011-04-06 07.57.36
BR0257I Your reply: ‘y’
BR0260E BRSPACE cancelled by user

BR1008I End of BRSPACE processing: sefphmbn.tbr 2011-04-06 07.57.36
BR0280I BRSPACE time stamp: 2011-04-06 07.57.37
BR1007I BRSPACE terminated with errors

Expert are always welcome for their valuable comment or suggestion for the above post.

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SAP BRTOOLS for tablespace extend

** Tested with UNIX / Solarise operating system.

In our organisation SAP is front end application. So as DBA we do have exposure on BRTOOL,BRSPACE etc.So just sharing the BR tool handling issue from todays onwards.

So here is one tested example for adding datafile in tablespace using the BRTOOL. Hopw you guys enjoy with this one…..!!!!

 

bash-3.00$ brtools
BR0651I BRTOOLS 7.00 (11)

BR0280I BRTOOLS time stamp: 2011-04-06 07.10.35
BR0656I Choice menu 1 – please make a selection
——————————————————————————-
BR*Tools main menu

 1 = Instance management
 2 – Space management
 3 – Segment management
 4 – Backup and database copy
 5 – Restore and recovery
 6 – Check and verification
 7 – Database statistics
 8 – Additional functions
 9 – Exit program

Standard keys: c – cont, b – back, s – stop, r – refr, h – help
——————————————————————————-
BR0662I Enter your choice:
2
BR0280I BRTOOLS time stamp: 2011-04-06 07.10.39
BR0663I Your choice: ‘2’

BR0280I BRTOOLS time stamp: 2011-04-06 07.10.39
BR0656I Choice menu 5 – please make a selection
——————————————————————————-
Database space management

 1 = Extend tablespace
 2 – Create tablespace
 3 – Drop tablespace
 4 – Alter tablespace
 5 – Alter data file
 6 – Move data file
 7 – Additional space functions
 8 – Reset program status

Standard keys: c – cont, b – back, s – stop, r – refr, h – help
——————————————————————————-
BR0662I Enter your choice:
1
BR0280I BRTOOLS time stamp: 2011-04-06 07.10.57
BR0663I Your choice: ‘1’

BR0280I BRTOOLS time stamp: 2011-04-06 07.10.57
BR0657I Input menu 81 – please check/enter input values
——————————————————————————-
BRSPACE options for tablespace extension

 1 – BRSPACE profile (profile) …… [initSAM.sap]
 2 – Database user/password (user) .. [/]
 3 ~ Tablespace name (tablespace) … []
 4 – Confirmation mode (confirm) …. [yes]
 5 – Scrolling line count (scroll) .. [20]
 6 – Message language (language) …. [E]
 7 – BRSPACE command line (command) . [-p initSAM.sap -s 20 -l E -f tsextend]

Standard keys: c – cont, b – back, s – stop, r – refr, h – help
——————————————————————————-
BR0662I Enter your choice:
3
BR0280I BRTOOLS time stamp: 2011-04-06 07.11.09
BR0663I Your choice: ‘3’

BR0280I BRTOOLS time stamp: 2011-04-06 07.11.09
BR0681I Enter string value for “tablespace” []:
3
BR0280I BRTOOLS time stamp: 2011-04-06 07.11.32
BR0683I New value for “tablespace”: ‘3’

BR0280I BRTOOLS time stamp: 2011-04-06 07.11.32
BR0657I Input menu 81 – please check/enter input values
——————————————————————————-
BRSPACE options for tablespace extension

 1 – BRSPACE profile (profile) …… [initSAM.sap]
 2 – Database user/password (user) .. [/]
 3 ~ Tablespace name (tablespace) … [3]
 4 – Confirmation mode (confirm) …. [yes]
 5 – Scrolling line count (scroll) .. [20]
 6 – Message language (language) …. [E]
 7 – BRSPACE command line (command) . [-p initSAM.sap -s 20 -l E -f tsextend -t 3]

Standard keys: c – cont, b – back, s – stop, r – refr, h – help
——————————————————————————-
BR0662I Enter your choice:
3
BR0280I BRTOOLS time stamp: 2011-04-06 07.12.55
BR0663I Your choice: ‘3’

BR0280I BRTOOLS time stamp: 2011-04-06 07.12.55
BR0681I Enter string value for “tablespace” [3]:

BR0280I BRTOOLS time stamp: 2011-04-06 07.13.17
BR0686I The value of “tablespace” was not changed

BR0280I BRTOOLS time stamp: 2011-04-06 07.13.17
BR0657I Input menu 81 – please check/enter input values
——————————————————————————-
BRSPACE options for tablespace extension

 1 – BRSPACE profile (profile) …… [initSAM.sap]
 2 – Database user/password (user) .. [/]
 3 ~ Tablespace name (tablespace) … [3]
 4 – Confirmation mode (confirm) …. [yes]
 5 – Scrolling line count (scroll) .. [20]
 6 – Message language (language) …. [E]
 7 – BRSPACE command line (command) . [-p initSAM.sap -s 20 -l E -f tsextend -t 3]

Standard keys: c – cont, b – back, s – stop, r – refr, h – help
——————————————————————————-
BR0662I Enter your choice:
3
BR0280I BRTOOLS time stamp: 2011-04-06 07.13.59
BR0663I Your choice: ‘3’

BR0280I BRTOOLS time stamp: 2011-04-06 07.13.59
BR0681I Enter string value for “tablespace” [3]:
PSAPSR3
BR0280I BRTOOLS time stamp: 2011-04-06 07.14.51
BR0683I New value for “tablespace”: ‘PSAPSR3’

BR0280I BRTOOLS time stamp: 2011-04-06 07.14.51
BR0657I Input menu 81 – please check/enter input values
——————————————————————————-
BRSPACE options for tablespace extension

 1 – BRSPACE profile (profile) …… [initSAM.sap]
 2 – Database user/password (user) .. [/]
 3 ~ Tablespace name (tablespace) … [PSAPSR3]
 4 – Confirmation mode (confirm) …. [yes]
 5 – Scrolling line count (scroll) .. [20]
 6 – Message language (language) …. [E]
 7 – BRSPACE command line (command) . [-p initSAM.sap -s 20 -l E -f tsextend -t PSAPSR3]

Standard keys: c – cont, b – back, s – stop, r – refr, h – help
——————————————————————————-
BR0662I Enter your choice:
c
BR0280I BRTOOLS time stamp: 2011-04-06 07.15.13
BR0663I Your choice: ‘c’
BR0259I Program execution will be continued…

BR0291I BRSPACE will be started with options ‘-p initSAM.sap -s 20 -l E -f tsextend -t PSAPSR3’

BR0280I BRTOOLS time stamp: 2011-04-06 07.15.13
BR0670I Enter ‘c[ont]’ to continue, ‘b[ack]’ to go back, ‘s[top]’ to abort:
c
BR0280I BRTOOLS time stamp: 2011-04-06 07.15.25
BR0257I Your reply: ‘c’
BR0259I Program execution will be continued…

###############################################################################

BR1001I BRSPACE 7.00 (11)
BR1002I Start of BRSPACE processing: sefphjwn.tse 2011-04-06 07.15.25

BR0280I BRSPACE time stamp: 2011-04-06 07.15.26
BR1009I Name of database instance: SAM
BR1010I BRSPACE action ID: sefphjwn
BR1011I BRSPACE function ID: tse
BR1012I BRSPACE function: tsextend

BR0280I BRSPACE time stamp: 2011-04-06 07.15.26
BR0657I Input menu 303 – please check/enter input values
——————————————————————————-
Options for extension of tablespace PSAPSR3 (1. file)

 1 * Last added file name (lastfile) ……. [/oracle/SAM/sapdata2/sr3_30/sr3.data30]
 2 * Last added file size in MB (lastsize) . [10240]
 3 – New file to be added (file) ……….. [/oracle/SAM/sapdata2/sr3_31/sr3.data31]
 4 ~ Raw disk / link target (rawlink) …… []
 5 – Size of the new file in MB (size) ….. [10240]
 6 – File autoextend mode (autoextend) ….. [no]
 7 # Maximum file size in MB (maxsize) ….. []
 8 # File increment size in MB (incrsize) .. []
 9 – SQL command (command) …………….. [alter tablespace PSAPSR3 add datafile ‘/oracle/SAM/sapdata2/sr3_31/sr3.data31’ size 10240M autoextend off]

Standard keys: c – cont, b – back, s – stop, r – refr, h – help
——————————————————————————-
BR0662I Enter your choice:
3
BR0280I BRSPACE time stamp: 2011-04-06 07.16.07
BR0663I Your choice: ‘3’

BR0280I BRSPACE time stamp: 2011-04-06 07.16.07
BR0681I Enter string value for “file” (<file>|<sapdata>|<N>) [/oracle/SAM/sapdata2/sr3_31/sr3.data31]:
/oracle/SAM/sapdata2/sr3_31/sr3.data31
BR0280I BRSPACE time stamp: 2011-04-06 07.17.24
BR0683I New value for “file”: ‘/oracle/SAM/sapdata2/sr3_31/sr3.data31’

BR0280I BRSPACE time stamp: 2011-04-06 07.17.24
BR0657I Input menu 303 – please check/enter input values
——————————————————————————-
Options for extension of tablespace PSAPSR3 (1. file)

 1 * Last added file name (lastfile) ……. [/oracle/SAM/sapdata2/sr3_30/sr3.data30]
 2 * Last added file size in MB (lastsize) . [10240]
 3 – New file to be added (file) ……….. [/oracle/SAM/sapdata2/sr3_31/sr3.data31]
 4 ~ Raw disk / link target (rawlink) …… []
 5 – Size of the new file in MB (size) ….. [10240]
 6 – File autoextend mode (autoextend) ….. [no]
 7 # Maximum file size in MB (maxsize) ….. []
 8 # File increment size in MB (incrsize) .. []
 9 – SQL command (command) …………….. [alter tablespace PSAPSR3 add datafile ‘/oracle/SAM/sapdata2/sr3_31/sr3.data31’ size 10240M autoextend off]

Standard keys: c – cont, b – back, s – stop, r – refr, h – help
——————————————————————————-
BR0662I Enter your choice:
c
BR0280I BRSPACE time stamp: 2011-04-06 07.17.49
BR0663I Your choice: ‘c’
BR0259I Program execution will be continued…

BR0280I BRSPACE time stamp: 2011-04-06 07.17.49
BR1091I Next data file can be specified now
BR0675I Do you want to perform this action?
BR0676I Enter ‘y[es]’ to perform the action, ‘n[o]/c[ont]’ to skip it, ‘s[top]’ to abort:
c
BR0280I BRSPACE time stamp: 2011-04-06 07.18.17
BR0257I Your reply: ‘c’
BR0678I The action will be skipped…
BR0259I Program execution will be continued…

BR0280I BRSPACE time stamp: 2011-04-06 07.18.17
BR0370I Directory /oracle/SAM/sapreorg/sefphjwn created

BR0280I BRSPACE time stamp: 2011-04-06 07.18.18
BR0319I Control file copy created: /oracle/SAM/sapreorg/sefphjwn/cntrlSAM.old 14237696

BR0280I BRSPACE time stamp: 2011-04-06 07.18.18
BR0370I Directory /oracle/SAM/sapdata2/sr3_31 created

BR0280I BRSPACE time stamp: 2011-04-06 07.18.18
BR1088I Extending tablespace PSAPSR3…

BR0280I BRSPACE time stamp: 2011-04-06 07.19.33
BR1016I SQL statement ‘alter tablespace PSAPSR3 add datafile ‘/oracle/SAM/sapdata2/sr3_31/sr3.data31′ size 10240M autoextend off’ executed successfully
BR1051I Tablespace PSAPSR3 extended successfully with file: /oracle/SAM/sapdata2/sr3_31/sr3.data31 10240M

BR0280I BRSPACE time stamp: 2011-04-06 07.19.33
BR0340I Switching to next online redo log file for database instance SAM…
BR0321I Switch to next online redo log file for database instance SAM successful

BR0280I BRSPACE time stamp: 2011-04-06 07.19.35
BR0319I Control file copy created: /oracle/SAM/sapreorg/sefphjwn/cntrlSAM.new 14237696

BR0280I BRSPACE time stamp: 2011-04-06 07.19.35
BR0670I Enter ‘c[ont]’ to continue, ‘b[ack]’ to go back, ‘s[top]’ to abort:
s
BR0280I BRSPACE time stamp: 2011-04-06 07.21.00
BR0257I Your reply: ‘s’
BR0679I Do you really want to cancel BRSPACE? Enter y[es]/n[o]:
yes
BR0280I BRSPACE time stamp: 2011-04-06 07.21.03
BR0257I Your reply: ‘yes’
BR0260E BRSPACE cancelled by user

BR1008I End of BRSPACE processing: sefphjwn.tse 2011-04-06 07.21.03
BR0280I BRSPACE time stamp: 2011-04-06 07.21.03
BR1007I BRSPACE terminated with errors

###############################################################################

BR0292I Execution of BRSPACE finished with return code 4

BR0668I Warnings or errors occurred – you can continue to ignore them or go back to repeat the last action
BR0280I BRTOOLS time stamp: 2011-04-06 07.21.03
BR0670I Enter ‘c[ont]’ to continue, ‘b[ack]’ to go back, ‘s[top]’ to abort:
s
BR0280I BRTOOLS time stamp: 2011-04-06 07.21.08
BR0257I Your reply: ‘s’
BR0679I Do you really want to cancel BRTOOLS? Enter y[es]/n[o]:
yes
BR0280I BRTOOLS time stamp: 2011-04-06 07.21.11
BR0257I Your reply: ‘yes’
BR0260E BRTOOLS cancelled by user

BR0280I BRTOOLS time stamp: 2011-04-06 07.21.11
BR0654I BRTOOLS terminated with errors
bash-3.00$

Expert are always welcome for their valuable comment or suggestion for the above post.

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Table Compression in Oracle

Recently i had to move a schema of size 70GB to another database[Oracle 10.2.0.1]. That was a readonly schema and never had any DML on any of the tables. In the new database i did compress the tables and the size was brought down from 70Gb to 22Gb.

1]Divided the tables based on the size.
2]Created the tablesapces.
3]Pre-created the tables on respective tablespaces.
4]Imported the tables.
5]Compressed and moved big tables from APP_BIG_TABLES_TEMP to APP_BIG_TABLES.
6]Rebuild the primary key indexes of the moved tables.
7]Droped APP_BIG_TABLES_TEMP.
8]Created the indexes.

The tables where create with PCTFREE 0 to take maximum advantage of the space in each extents as i was sure that never an UPDATE would happen on any of these tables.

Compress statement with “move”
======================
ALTER TABLE <table_name> MOVE TABLESPACE <to new tablespace> COMPRESS NOLOGGING PARALLEL (degree N);
eg: ALTER TABLE SALES_INFORMATION MOVE TABLESPACE APP_BIG_TABLES COMPRESS NOLOGGING PARALLEL (degree 8);

COMPRESS alone will only compress the tables, to recalim the space use MOVE in the statement.
My Server had 32 CPUs, but i just used 8. I should leave the rest for other applications.

To move tables with LOB segments:
ALTER TABLE <TABLE_NAME> MOVE TABLESPACE <new_tablespace> LOB(<lob_column_1) STORE AS (TABLESPACE <new_tablespace) LOB(<lob_column_2) STORE AS (TABLESPACE <new_tablespace);

Why did not i compress and move the table in the same tablespace?
COMPRESS and MOVE of tables in the same tablespace will not bring down the datafiles high water mark and i will not be able to resize the datafiles to a smaller size. So i found it easy to drop the very big APP_BIG_TABLES_TEMP once the tables were compressed and moved to APP_BIG_TABLES.

BEFORE COMPRESS
================
OBJECT_TYPE COUNT SIZE(in GB)
—————— ———- ———-
INDEX 110 7.73681641
TABLE 55 62.6555786
———-
sum 70.392395
AFTER COMPRESS
===============
OBJECT_TYPE COUNT SIZE(in GB)
—————— ———- ———-
INDEX 110 2.375
TABLE 55 19.8398438
———-
sum 22.2148438

Expert are always welcome for their valuable comment or suggestion for the above post.

 

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Step by Step Upgrading Oracle 10g to Oracle 11g

Recently we did database upgrade from 10g to Oracle 11g.I would like share that activity with you.

Pre-Requisite:

You should have the Oracle database 10g, which you want to migerate.
Also here we are upgrading to Oracle Database 11g – Beta 6 (11.1.0.6)

Step 1) Installing Oracle 11g Home

We cannot upgrade the existing Oracle Home, since 11g is not a patchset. We have to install 11g oracle home as a seperate ORACLE_HOME in parallel to 10g Oracle Home.

Example my 10g Oracle Home is : /u01/app/oracle/oracle/product/10.2.0

then my 11g Oracel Home is : /u01/app/oracle/oracle/product/11.1.0

Just a parallel 11.1.0 directory can be created and we can install oracle home in this location.

Start the installation using the below command

./runInstaller -invPtrLoc /u01/app/oracle/oracle/product/11.1.0/oraInst

Screen 1 – Select Product Install
select “Oracle Database 11g”

Screen 2 – Select Installation Method
Choose “Advanced Installation”

Screen 3 – Specify Inventory directory and creditials
Note: We are providing local inventory here inside the corresponding ORACLE_HOME location.

Screen 4 – Select Installation Type
Choose “Enterprise Edition”

Screen 5 – Installation Location
Oracle Base as parent directory of ORACLE HOME

Screen 6 – Product Specific Pre-requisite Checks
It may gives below warning, we can ignore and proceed further

Screen 7 – Upgrade an Existsing Database
Choose “No”

Screen 8 – Select Configuration Option
Choose “Install Software Only”

Screen 9 – Privileged system groups

Based on the group of oracle user, this value has to be set.

Screen 10 – Summary
Click on “Install”

At the end of installation, installer will ask to run root.sh script. Do not press OK button.
Run root.sh as a root user and once done, press OK button. This will complete the software installation for Oracle Database 11g.

Step 2) Pre-Upgrade Utility

In 11g Home you installed, go to $ORACLE_HOME/rdbms/admin and copy the file utlu111i.sql to some temp location.

[oracle]$ cd $ORACLE_HOME
[oracle]$ cd rdbms/admin/
[oracle]$ pwd
/u01/app/oracle/oracle/product/product/11.1.0/db_1/rdbms/admin
[oracle]$ cp utlu111i.sql /tmp

The utility will give the output in the form of recommendations to be implemented before starting the upgrade. Unless these requirements are met, the upgrade will fail.

Most of the time issue use to come up with time zone….

Then login to the 10g oracle database and run the above sql you copied.

Oracle Database 11.1 Pre-Upgrade Information Tool 23-02-2011 01:34:07
.
**********************************************************************
Database:
**********************************************************************
–> name: ORCL
–> version: 10.2.0.1.0
–> compatible: 10.2.0.1.0
–> blocksize: 8192
–> platform: Linux IA (32-bit)
–> timezone file: V2
.
**********************************************************************
Tablespaces: [make adjustments in the current environment]
**********************************************************************
–> SYSTEM tablespace is adequate for the upgrade.
.
.
.
.
WARNING: –> Database contains schemas with objects dependent on network
packages.
…. Refer to the 11g Upgrade Guide for instructions to configure Network ACLs.
…. USER SYSMAN has dependent objects.
WARNING: –> EM Database Control Repository exists in the database.
…. Direct downgrade of EM Database Control is not supported. Refer to the
…. 11g Upgrade Guide for instructions to save the EM data prior to upgrade.
.

PL/SQL procedure successfully completed.

The utility will give the output in the form of recommendations to be implemented before starting the upgrade. Unless these requirements are met, the upgrade will fail.

Step 3) Executing the recommended steps

Following are the critical steps to be executed based on above warnings. These commands are to be executed while connecting to database from 10g Oracle Home

WARNING: –> Database is using an old timezone file version.
…. Patch the 10.2.0.1.0 database to timezone file version 4
…. BEFORE upgrading the database. Re-run utlu111i.sql after
…. patching the database to record the new timezone file version.

Finding the Version of existing timezone files:

SQL> select * from v$timezone_file;

FILENAME VERSION
———— ———-
timezlrg.dat 2

SQL> SELECT CASE COUNT(DISTINCT(tzname))
WHEN 183 then 1
WHEN 355 then 1
WHEN 347 then 1
WHEN 377 then 2
WHEN 186 then case COUNT(tzname) WHEN 636 then 2 WHEN 626 then 3 ELSE 0 end
WHEN 185 then 3
WHEN 386 then 3
WHEN 387 then case COUNT(tzname) WHEN 1438 then 3 ELSE 0 end
WHEN 391 then case COUNT(tzname) WHEN 1457 then 4 ELSE 0 end
WHEN 392 then case COUNT(tzname) WHEN 1458 then 4 ELSE 0 end
WHEN 188 then case COUNT(tzname) WHEN 637 then 4 ELSE 0 end
WHEN 189 then case COUNT(tzname) WHEN 638 then 4 ELSE 0 end
ELSE 0 end VERSION
FROM v$timezone_names;

VERSION
———-
2

If the Version of the existing timezone is less than 4, then apply the patch for Version 4 timezone files.

Check the database version

SQL> select banner from v$version;

BANNER
—————————————————————-
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 – Prod
PL/SQL Release 10.2.0.1.0 – Production
CORE 10.2.0.1.0 Production
TNS for Linux: Version 10.2.0.1.0 – Production
NLSRTL Version 10.2.0.1.0 – Production

For 10.2.0.1 check the metalink note ID 413671.1. We have a table which defines the patch to be applied.

Always try to use the official patch
The script (and on 10g also the csv file) are normally delivered through installation of a patch in the Oracle home. Please note that before using this note you are advised to double check that the time zone patches are not available for your patchset. Applying the “correct” patch through opatch is always preferable to the manual method described in this note.

If there is no official patchset for the version you are currently having then you can Identify the utltzuv2.sql & timezdif.csv combination patch for a different patchset, but same release.

For example if you run 10.2.0.1 and you are trying to find the utltzuv2.sql script & timezdif.csv file you can find the correct patch 5632264 for 10.2.0.2 and this will be applicable to 10.2.0.1 as well.

Please follow the metalink note ID 396387.1

Once you identify the correct patchset(5632264 for 10.2.X), download the same and unzip it.
[oracle]$ unzip p5632264_10202_LINUX.zip
[oracle]$ ls
etc files README.txt
[oracle]$ cd files/oracore/zoneinfo
[oracle]$ ls
readme.txt timezlrg.dat timezone.dat

Backup $ORACLE_HOME/oracore/zoneinfo directory

[oracle]$ cp -R $ORACLE_HOME/oracore/zoneinfo $ORACLE_HOME/oracore/zoneinfo_backup

Copy the .dat files

[oracle]$ cp timezone.dat timezlrg.dat $ORACLE_HOME/oracore/zoneinfo

Bounce the database and check the TIMEZONE version again

SQL> select * from v$timezone_file;

FILENAME VERSION
———— ———-
timezlrg.dat 4

SQL> SELECT CASE COUNT(DISTINCT(tzname))
WHEN 183 then 1
WHEN 355 then 1
WHEN 347 then 1
WHEN 377 then 2
WHEN 186 then case COUNT(tzname) WHEN 636 then 2 WHEN 626 then 3 ELSE 0 end
WHEN 185 then 3
WHEN 386 then 3
WHEN 387 then case COUNT(tzname) WHEN 1438 then 3 ELSE 0 end
WHEN 391 then case COUNT(tzname) WHEN 1457 then 4 ELSE 0 end
WHEN 392 then case COUNT(tzname) WHEN 1458 then 4 ELSE 0 end
WHEN 188 then case COUNT(tzname) WHEN 637 then 4 ELSE 0 end
WHEN 189 then case COUNT(tzname) WHEN 638 then 4 ELSE 0 end
ELSE 0 end VERSION
FROM v$timezone_names;

VERSION
———-
4

WARNING: –> Database contains stale optimizer statistics.
…. Refer to the 11g Upgrade Guide for instructions to update
…. statistics prior to upgrading the database.
…. Component Schemas with stale statistics:
…. SYS
…. SYSMAN

Gather Dictionary stats:

Connect as sys user and gather statistics
SQL> EXEC DBMS_STATS.GATHER_DICTIONARY_STATS;

SQL> EXEC DBMS_STATS.GATHER_SCHEMA_STATS(‘SYS’);

PL/SQL procedure successfully completed.

SQL> EXEC DBMS_STATS.GATHER_SCHEMA_STATS(‘SYSMAN’);

PL/SQL procedure successfully completed.

Step 4) Run Pre-Upgrade Utility again

After executing the recommended steps, run the pre-upgrade utility once again to make sure, you don’t get any critical warnings.

Run the pre-upgrade utility script on 10g database while connecting from 10g oracle home.

If every thing looks fine, Shut down the database from 10g Oracle Home

This time make sure you dont have the critical warnings like the one with TIMEZONE version.

Step 5) Starting Upgrade

Source the following variables for 11g Oracle Home

[oracle]$ export ORACLE_HOME=/u01/app/oracle/oracle/product/product/11.1.0/db_1
[oracle]$ export PATH=$ORACLE_HOME/bin:$PATH
[oracle]$ export ORACLE_SID=orcl
[oracle]$ export TNS_ADMIN=$ORACLE_HOME/network/admin

connected to the database sys as sysdba

sqlplus “/ as sysdba” –> will be connected to idle instance

SQL> startup upgrade
ORA-32004: obsolete and/or deprecated parameter(s) specified
ORACLE instance started.

Total System Global Area 611000320 bytes
Fixed Size 1301588 bytes
Variable Size 201327532 bytes
Database Buffers 402653184 bytes
Redo Buffers 5718016 bytes
Database mounted.
Database opened.
SQL> SPOOL upgrade.log
SQL> @catupgrd.sql

Once the upgrades finishes. It will shut down the database automatically.
Login again as sysdba and startup in normal mode.

Check the dba_registry for the components and its status

Step 6) Post-Upgrade Steps

Once the upgrade completes, restart the instance to reinitialize the system parameters for normal operation.

SQL> STARTUP

Run utlu111s.sql to display the results of the upgrade:

SQL> @?/rdbms/admin/utlu111s.sql
.
Oracle Database 11.1 Post-Upgrade Status Tool 23-02-2011 05:22:40
.
Component Status Version HH:MM:SS
.
Oracle Server
. VALID 11.1.0.6.0 00:19:02
JServer JAVA Virtual Machine
. VALID 11.1.0.6.0 00:02:55
Oracle Workspace Manager
. VALID 11.1.0.6.0 00:00:54
OLAP Analytic Workspace
. VALID 11.1.0.6.0 00:00:26
OLAP Catalog
. VALID 11.1.0.6.0 00:00:58
Oracle OLAP API
. VALID 11.1.0.6.0 00:00:25
Oracle Enterprise Manager
. VALID 11.1.0.6.0 00:11:00
Oracle XDK
. VALID 11.1.0.6.0 00:00:53
Oracle Text
. VALID 11.1.0.6.0 00:00:50
Oracle XML Database
. VALID 11.1.0.6.0 00:03:52
Oracle Database Java Packages
. VALID 11.1.0.6.0 00:00:21
Oracle Multimedia
. VALID 11.1.0.6.0 00:04:25
Spatial
. VALID 11.1.0.6.0 00:05:18
Oracle Expression Filter
. VALID 11.1.0.6.0 00:00:13
Oracle Rules Manager
. VALID 11.1.0.6.0 00:00:12
Gathering Statistics
. 00:04:03
Total Upgrade Time: 00:55:57

PL/SQL procedure successfully completed.

Run catuppst.sql, located in the ORACLE_HOME/rdbms/admin directory, to perform upgrade actions that do not require the database to be in UPGRADE mode:

SQL> @?/rdbms/admin/catuppst.sql

Run utlrp.sql to recompile

SQL> select count(*) from dba_objects
2 where status = ‘INVALID’;

COUNT(*)
———-
1576

SQL> @?/rdbms/admin/utlrp.sql

SQL> select count(*) from dba_objects
2 where status = ‘INVALID’;

COUNT(*)
———-
0

This completes the upgrade.

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How to adjust the high watermark in ORACLE 10g – ALTER TABLE SHRINK

Yesterday my junior team member was confused about fragmentation and High water mark concepts.Also there was good comment on my fragmentation post, so it inspire me to write something about the High Watermark and the Oracle 10gR1 New Feature SEGMENT SHRINKING.About fragmentation I have already disscused in my previous post.

The High Watermark is the maximum fill-grade a table has ever reached.
Above the high watermark are only empty blocks.
These blocks can be formatted or unformatted.

First let’s have a look at the question when space is allocated

– when you create a table at least one extent (contiguous blocks) is allocated to the table
– if you have specified MINEXTENTS the number of MINEXTENTS extents
will be allocated immedaitely to the table
– if you have not specified MINEXTENTS then exactely one extent
will be allocated .

Immediately after creation of the segment (table) the high watermark will be at the first block of the first extent as long as there are no inserts made.

When you insert rows into the table the high watermark will be bumped up step by step.
This is done by the server process which makes the inserts.

Now let us take a look at when space is released again from a segment like a table or index:

Let’s asume that we have filled a table with 100’0000 rows.
And let’s asume that we deleted 50’000 rows afterwards.
In this case the high watermark will have reached the level of 100’000 and will have stayed there. Which means that we have empty blocks below the high watermark now.
Oracle has a good reason this: it might occur that you delete rows and immediately this you insert rows into the same table. In this case it is good that the space was not released with the deletes, because it had to be get reallocate again for the following inserts, which would mean permanent changes to the data dictionary
(=> dba_free_space, dba_extents, dba_segements …) .
Furthermore the physical addresses of the deleted row get recycled by new rows.

These empty blocks below the high watermark can get annoying in a number of situations because they are not used by DIRECT LOADs and DIRECT PATH LOADs:

1. seriell direct load:
INSERT /*+ APPEND */
INTO hr.employees
NOLOGGING
SELECT *
FROM oe.emps;

2. parallel direct load:
ALTER SESSION ENABLE PARALLEL DML;
INSERT /*+PARALLLEL(hr.employees,2)
INTO hr.employees
NOLOGGING
SELECT *
FROM oe.emps;

3. direct path loads:
sqlldr hr/hr control=lcaselutz.ctl … direct=y (default is direct=n)

All the above actions case that the SGA is not used for the inserts but the PGA:
there wil be temporary segements filled and dumped into newly formatted blocks above the high watermark.

So we might want to get high watermark down before we load data into the table in order to use the free empty blocks for the loading.

So how can we release unused space from a table?

There are a number of possible options which are already available before Oracle 10g:
– What we always could do is export and import the segment.
After an import the table will have only one extent.
The rows will have new physical addresses and
the high watermark will be adjusted.
– Another option would be to TRUNCATE the table.
With this we would loose all rows which are in the table.
So we cannot use this if we want to keep existing records.

With Oracle 9i another possibilty was implemented:
ALTER TABLE emp MOVE TABLESPACE users;
This statement will also cause that
– the rows will have new physical addresses and
– the high watermark will be adjusted.
But for this:
– we need a full (exclusive) table lock
– the indexes will be left with the status unusable (because they contain the old rowids) and must be rebuilt.

Starting with ORACLE 10gR1 we can use a new feature for adjusting the high watermark,
it is called segment shrinking and is only possible for segments which use ASSM, in other words, which are located in tablespaces which use Automatic Segement Space Management.
In such a tablespace a table does not really have a High watermark!
It uses two watermarks instead:
– the High High Watermark referred to as HHWM, above which alle blocks ar unformatted.
– the Low High Watermark referred to as LHWM below which all blocks are formatted.
We now can have unformatted blocks in the middle of a segment!

ASSM was introduced in Oracle 9iR2 and it was made the default for tablespaces in Oracle 10gR2.
With the table shrinking feature we can get Oracle
to move rows which are located in the middle or at the end of a segment
further more down to the beginning of the segment and by
this make the segment more compact.
For this we must first allow ORACLE to change the ROWIDs of these rows by issuing
ALTER TABLE emp ENABLE ROW MOVEMENT;
ROWIDs are normally assigned to a row for the life time of the row at insert time.

After we have given Oracle the permission to change the ROWIDs
we can now issue a shrink statement.
ALTER TABLE emp SHRINK SPACE;

This statement will procede in two steps:
– The first step makes the segment compact
by moving rows further down to free blocks at the beginning of the segment.
– The second step adjusts the high watermark. For this Oracle needs an exclusive table lock,
but for a very short moment only.

Table shrinking…
– will adjust the high watermark
– can be done online
– will cause only rowlocks during the operation and just a very short full table lock at the end of the operation
– indexes will be maintained and remain usable
– can be made in one go
– can be made in two steps
(this can be usefull if you cannot get a full table lock during certain hours:
you only make the first step and adjust the high watermark later
when it is more conveniant:

– ALTER TABLE emp SHRINK SPACE; – only for the emp table
– ALTER TABLE emp SHRINK SPACE CASCADE; – for all dependent objects as well

– ALTER TABLE emp SHRINK SPACE COMPACT; – only makes the first step (moves the rows)

How are the indexes maintained?
In the first phase Oracle scans the segment from the back to find the position of the last row.
Afterwards it scan the segment from the beginning to find the position of the first free slot in a block in this segment. In case the two positions are the same, there is nothing to shrink. In case the two positions are different Oracle deletes the row from the back and inserts it into the free position at front of the segement. Now Oracle scan the segement from the back and front again and again until it finds that the two positions are the same.
Since it is DML statements performed to move the rows, the indexes are maintained at the same time. Only row level locks are used for these operations in the first pase of SHRINK TABLE statement.

The following restrictions apply to table shrinking:

1.) It is only possible in tablespaces with ASSM.
2.) You cannot shrink:
– UNDO segments
– temporary segments
– clustered tables
– tables with a colmn of datatype LONG
– LOB indexes
– IOT mapping tables and IOT overflow segments
– tables with MVIEWS with ON COMMIT
– tables with MVIEWS which are based on ROWIDs

The Oracle 10g Oracle comes with a Segment Advisor utility.
The Enterprise Manager, Database Control, even has a wizzard which can search for shrink candidates.

This advisor is run automatically by an autotask job on a regular basis in the default maintainance window.

You can use the built in package DBMS_SPACE to run the advisor manually as well.
I will blog about this later on some time.

Expert are always welcome for their valuable comment or suggestion for the above post.

Related Post:

https://samadhandba.wordpress.com/2011/01/20/table-fragmentation-how-to-avoid-same/

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