AskDba.org Weblog

There are situations when we see “temporary segments” in permanent tablespaces hanging around and not getting cleaned up.
These temporary segments in permanent tablespace can be created by DDL operations like CTAS and “alter index..rebuild” because
the new object is created as a temporary segment in the target tablespace and when the DDL action finishes it will be changed to permanent type.
These temporary segments take actual disk space when SMON fails to perform its assigned job to cleanup stray temporary segments.
Following query finds out these segments:

 SQL > select tablespace_name, owner, sum(bytes/1024/1024) from dba_segments
where segment_type = 'TEMPORARY' group by tablespace_name, owner;

TABLESPACE_NAME     OWNER          SEGMENT_NAME     SUM(BYTES/1024/1024)
------------------- ------------   ------------     --------------------
xxxx_DATA           SYS              123.8365          137706
BDEPST_INDEX        SYS              345.8756            8910
KMRPT_DATA          SYS                345.87       25284.875
BILL_INDEX          SYS                                   .25
DSS_DATA            SYS                                   798
MRKT_INDEX          SYS                                   208
SPCT_DATA           SYS                              69642.25
SPCT_INDEX          SYS                              956.4375

Here we can see that tablespace KMRPT_DATA, SPCT_INDEX and SPCT_DATA have large temporary segments.

To know if any DDL is active which can create temporary segments we can use the following:

SQL> conn / as sysdba
SQL> select owner FROM dba_segments WHERE segment_name='345.87';
SQL> select pid from v$process where username='owner from above query';
SQL> alter session set tracefile_identifier='TEMPORARY_SEGMENTS';
SQL> oradebug setorapid <pid obtained>
SQL> oradebug dump errorstack 3
SQL > oradebug tracefile_name

It will give you the tracefile name, open that file and check for the “current sql”
If it is a DDL like CTAS or index rebuild, then wait for the operation to complete. If there is no pid
returned then these segments are “stray segements” and needs to cleaned up manually.

There are two ways to force the drop of temporary segments:

1. Using event DROP_SEGMENTS
2. Corrupting the segments and dropping these corrupted segments.

1. Using DROP_segments:

Find out the tablespace number (ts#) which contains temporary segments:
SQL> select ts# from sys.ts$ where name = 'tablespace name';

Suppose it comes out to be 10, use the following command to cleanup temporary segments:

SQL> alter session set events 'immediate trace name DROP_SEGMENTS level 11';

level is ts#+1 i.e 10+1=11 in this case.

2. Corrupting temporary segments for drop:
For this following procedures are used:
- DBMS_SPACE_ADMIN.TABLESPACE_VERIFY
- DBMS_SPACE_ADMIN.SEGMENT_CORRUPT
- DBMS_SPACE_ADMIN.SEGMENT_DROP_CORRUPT

– Verify the tablespace that contains temporary segments (In this case it is KMRPT_DATA)

SQL&gt; exec <span style="color: #ff0000;">DBMS_SPACE_ADMIN.TABLESPACE_VERIFY</span>('KMRPT_DATA');

– Corrupt the temporary segments in tablespace KMRPT_DATA

SQL&gt; select 'exec <span style="color: #ff0000;">DBMS_SPACE_ADMIN.SEGMENT_CORRUPT</span>(' || chr(39) || tablespace_name || chr(39) || ',' || HEADER_FILE || ',' || HEADER_BLOCK || ');'  from dba_segments where SEGMENT_TYPE like 'TEMP%' and tablespace_name = 'KMRPT_DATA';

– Drop the corrupted temporary segments

SQL&gt; select 'exec <span style="color: #ff0000;">DBMS_SPACE_ADMIN.SEGMENT_DROP_CORRUPT</span> (' || chr(39) || tablespace_name || chr(39) || ',' || HEADER_FILE || ',' || HEADER_BLOCK || ');' from dba_segments where SEGMENT_TYPE like 'TEMP%' and tablespace_name = 'KMRPT_DATA';

– Verify the tablespace again to update the new dictionary information:

SQL&gt; EXECUTE <span style="color: #ff0000;">DBMS_SPACE_ADMIN.TABLESPACE_VERIFY</span>('KMRPT_DATA');

This will remove temporary segments from permanent tablespace.

Cheers!!!

Saurabh Sood