Thinking Out Loud

May 5, 2018

DBFS Nightmare

Filed under: 12c,GoldenGate — mdinh @ 4:19 pm
====================================================================================================
How to cleanup DBFS tablespace after removing files at DBFS filesystem (Doc ID 2331565.1)	
====================================================================================================
High level overview of the DBMS_DBFS_SFS.REORGANIZEFS procedure:
----------------------------------------------------------------------------------------------------
1) Create a NEW tablespace
2) Create a temporary filesystem with dbms_dbfs_sfs.createFilesystem in the new tablespace.
3) Run dbms_dbfs_sfs.reorganizeFS -->>
   EXEC DBMS_DBFS_SFS.REORGANIZEFS(SRCSTORE=>'FS_FS1', DSTSTORE=>'FS_TMP_FS');
4) The dbfs data is now in the smaller NEW tablespace.
5) Drop the temporay filesystem with dbms_dbfs_sfs.dropFilesystem
6) The OLD original tablespace is empty now.
----------------------------------------------------------------------------------------------------
To reuse the same tablespace again please follow the below steps
----------------------------------------------------------------------------------------------------
7) Create a temporary filesystem with dbms_dbfs_sfs.createFilesystem in the OLD ORIGINAL tablespace.
8) Run dbms_dbfs_sfs.reorganizeFS
9) The dbfs data is now in the smaller the ORIGINAL tablespace.
10) Drop the temporay filesystem with dbms_dbfs_sfs.dropFilesystem
11) The NEW small tablespace is empty now and can be dropped.

====================================================================================================
DBFS tablespace keep growing not using expired blocks (Doc ID 2327299.1)	
====================================================================================================
----------------------------------------------------------------------------------------------------
First perform the DBFS re-org to cleanup the tablespace after removing the files at file system level by following below document
----------------------------------------------------------------------------------------------------
How to cleanup DBFS tablespace after removing files at DBFS filesystem (Doc ID 2331565.1)

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After the re-org, set the  below parameter to reuse the expired blocks
----------------------------------------------------------------------------------------------------
ALTER SYSTEM SET "_ENABLE_SPACE_PREALLOCATION" = 0;

====================================================================================================
ORA-1654 - DBFS FREE SPACE NOT RECLAIMED AFTER CLEARING FILES (Doc ID 1948305.1)	
====================================================================================================
----------------------------------------------------------------------------------------------------
a) Check Lob retention setting:
----------------------------------------------------------------------------------------------------
  ex. SQL> select 
  table_name,retention_type,retention_value,retention,securefile from dba_lobs 
  where table_name = 'T_FS1';

----------------------------------------------------------------------------------------------------  
b) Change LOB retention to none.
----------------------------------------------------------------------------------------------------
  ex. SQL> alter table DBFS_USER.T_FS1 modify lob (FILEDATA) (retention none);

After countless discussions, team found GOLD.

12.1 Shrinking and Reorganizing DBFS Filesystems

STEPS:

sqlplus /as sysdba
create bigfile tablespace DBFS_NEW datafile size 8G autoextend on next 1G maxsize 70G;
grant dba to dbfs_user;
alter user dbfs_user default role all;
exit

+++ REORGANIZE DBFS FILESYSTEM FS1 IN TABLESPACE DBFS_TS INTO A NEW TABLESPACE DBFS_NEW, 
+++ USING A TEMPORARY FILESYSTEM NAMED TMP_FS, WHERE ALL FILESYSTEMS BELONG TO DATABASE USER DBFS_USER
cd $ORACLE_HOME/rdbms/admin
sqlplus dbfs_user
@dbfs_create_filesystem DBFS_NEW TMP_FS
exec dbms_dbfs_sfs.reorganizefs('FS1','TMP_FS');
@dbfs_drop_filesystem TMP_FS
purge user_recyclebin;
exit

sqlplus / aa sysdba 
revoke dba from dbfs_user;
select count(*) from dba_extents where tablespace_name='DBFS_TS'; 
select count(*) from dba_extents where tablespace_name='DBFS_NEW'; 
-- DROP TABLESPACE HAVING ZERO EXTENTS
-- BE CAREFUL IN CASE USER AND DBFS ARE USING SAME TABLESPACE
Example:
create user dbfs_user identified by **** default tablespace dbfs_ts quota unlimited on dbfs_ts;
@$ORACLE_HOME/rdbms/admin/dbfs_create_filesystem.sql dbfs_ts FS1

TRUE CONFESSION:

I created an imperfect plan at first that might have saved me from a major catastrophe.

Create DBFS_TMP in a separate Disk Group since I was concern existing may not have enough storage.
Reorg from DBFS_TS to DBFS_TMP (bad idea to name tablespace as DBFS_TMP as LOB Segments migrated here).
Reorg from DBFS_TMP back to DBFS_TS.
Drop tablespace DBFS_TMP.

There’s 29G difference between old and new. How much if this space will be reclaimable due to HWM in data file?

Performing reorg twice is really not an option in prod.

RESULTS:

SEGMENT_NAME                   TABLESPACE_NAME                        MB    EXTENTS
------------------------------ ------------------------------ ---------- ----------
LOB_SFS$_FST_1                 DBFS_TS                        30647.1875       1851
LOB_SFS$_FST_6225924           DBFS_NEW                         1025.125        130

WARNINGS:

This has only been tested in a vacuum (non-prod env w very low activities) – YMMV.

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