Tag: linux
- Written by: ilmarkerm
- Category: Blog entry
- Published: August 7, 2014
When cloning pluggable databases Oracle gives you also SNAPSHOT COPY clause to utilize storage system snapshot capabilities to save on storage space. But it works only when datafiles are placed on ACFS, ZFS Appliance over DNFS or Netapp (Oracle Multitenant Pluggable Database Snapshot Cloning: Use Cases and Supported Platforms Doc ID 1597027.1) and you also cannot unplug/drop the source PDB and you also cannot unplug the clone PDB.
Recently I’ve started to like BTRFS (only on test systems!) and it also has builting snapshot capabilities. In this article I’ll try to use BTRFS snapshots to create pluggable database clones. It is not as automated as Oracle builtin snapshots, but possible.
What I have before cloning:
SQL> select name, open_mode, guid from v$pdbs;
NAME OPEN_MODE GUID
------------------------------ ---------- --------------------------------
PDB$SEED READ ONLY FFCDD773320B2767E0432700FA0A06D0
DB1 MOUNTED FFCC6C3F473E124BE0432700FA0A429E
DB2 READ WRITE 000A7D190B3C15A1E0532700FA0A3C10
SQL> alter session set container=db2;
Session altered.
SQL> select round(bytes/1024/1024) mb, file_name from dba_data_files;
MB FILE_NAME
---------- -------------
280 /u01/db2/system01.dbf
690 /u01/db2/sysaux01.dbf
5 /u01/db2/users01.dbf
100 /u01/db2/tdata01.dbf
2048 /u01/db2/tlarge01.dbf
My goal is to clone DB2 to new PDB called DB3. Currently my DB2 is stored under /u01/db2/ that is a dedicated subvolume under BTRFS filesystem /u01. The file system is currently using 21.23GB.
[root@cdbtest u01]# btrfs subvolume list -a -t /u01
ID gen top level path
-- --- --------- ----
256 1543 5 app
281 736 5 app_bak
285 1545 5 data
286 1297 5 data_bak
287 1544 5 db2
289 1333 5 db2_bak
[root@cdbtest u01]# ls -l /u01/db2
total 3198048
-rw-r----- 1 oracle oinstall 723525632 Aug 7 17:40 sysaux01.dbf
-rw-r----- 1 oracle oinstall 293609472 Aug 7 17:42 system01.dbf
-rw-r----- 1 oracle oinstall 104865792 Aug 7 17:21 tdata01.dbf
-rw-r----- 1 oracle oinstall 20979712 Aug 7 16:56 temp01.dbf
-rw-r----- 1 oracle oinstall 2147491840 Aug 7 17:21 tlarge01.dbf
-rw-r----- 1 oracle oinstall 5251072 Aug 7 17:21 users01.dbf
[root@cdbtest u01]# btrfs filesystem df /u01
Data: total=29.01GB, used=21.23GB
System, DUP: total=8.00MB, used=4.00KB
System: total=4.00MB, used=0.00
Metadata, DUP: total=1.00GB, used=124.73MB
Metadata: total=8.00MB, used=0.00
Now, lets start. First need to open DB2 read only and create description XML file from it:
SQL> exec dbms_pdb.describe(pdb_descr_file=>'/u01/db2_pdb.xml');
PL/SQL procedure successfully completed.
And create a BTRFS snapshot under directory /u01/db3
[root@cdbtest u01]# btrfs subvolume snapshot db2 db3
Create a snapshot of 'db2' in './db3'
[root@cdbtest u01]# btrfs filesystem df /u01
Data: total=29.01GB, used=21.23GB
System, DUP: total=8.00MB, used=4.00KB
System: total=4.00MB, used=0.00
Metadata, DUP: total=1.00GB, used=124.75MB
Metadata: total=8.00MB, used=0.00
[root@cdbtest u01]# ls -l
total 8
drwxr-xr-x 1 oracle oinstall 50 Aug 4 11:55 app
drwxr-xr-x 1 oracle oinstall 50 Aug 4 11:55 app_bak
drwxrwxr-x 1 oracle oinstall 60 Aug 5 15:16 data
drwxrwxr-x 1 oracle oinstall 60 Aug 5 15:16 data_bak
drwxr-xr-x 1 oracle oinstall 136 Aug 7 17:53 db2
drwxr-xr-x 1 oracle oinstall 112 Aug 7 15:47 db2_bak
-rw-r--r-- 1 oracle oinstall 6370 Aug 7 17:53 db2_pdb.xml
drwxr-xr-x 1 oracle oinstall 136 Aug 7 17:53 db3
[root@cdbtest u01]# ls -l db3
total 3198048
-rw-r----- 1 oracle oinstall 723525632 Aug 7 17:49 sysaux01.dbf
-rw-r----- 1 oracle oinstall 293609472 Aug 7 17:49 system01.dbf
-rw-r----- 1 oracle oinstall 104865792 Aug 7 17:49 tdata01.dbf
-rw-r----- 1 oracle oinstall 20979712 Aug 7 16:56 temp01.dbf
-rw-r----- 1 oracle oinstall 2147491840 Aug 7 17:49 tlarge01.dbf
-rw-r----- 1 oracle oinstall 5251072 Aug 7 17:49 users01.dbf
I have a snapshot now and no additional space used! 🙂 Lets try to connect it as a new PDB.
SQL> alter session set container=cdb$root;
Session altered.
SQL> create pluggable database db3 using '/u01/db2_pdb.xml' source_file_name_convert=('/u01/db2/','/u01/db3/') nocopy tempfile reuse;
create pluggable database db3 using '/u01/db2_pdb.xml' source_file_name_convert=('/u01/db2/','/u01/db3/') nocopy tempfile reuse
*
ERROR at line 1:
ORA-65122: Pluggable database GUID conflicts with the GUID of an existing container.
Simple plug in does not work, since the database already has a PDB with the same GUID. Create pluggable database command has a AS CLONE clause to generate new GUID and DBID values.
SQL> create pluggable database db3 AS CLONE using '/u01/db2_pdb.xml' source_file_name_convert=('/u01/db2/','/u01/db3/') nocopy tempfile reuse;
Pluggable database created.
SQL> select name, open_mode, guid from v$pdbs;
NAME OPEN_MODE GUID
------------------------------ ---------- --------------------------------
PDB$SEED READ ONLY FFCDD773320B2767E0432700FA0A06D0
DB1 MOUNTED FFCC6C3F473E124BE0432700FA0A429E
DB2 READ ONLY 000A7D190B3C15A1E0532700FA0A3C10
DB3 MOUNTED 000C54AE44352331E0532700FA0AFA69
SQL> alter session set container=db3;
Session altered.
SQL> select name from v$datafile;
NAME
----------------------------------------------------
/u01/data/CDB2/datafile/o1_mf_undotbs1_9xyyw5dc_.dbf
/u01/db3/system01.dbf
/u01/db3/sysaux01.dbf
/u01/db3/users01.dbf
/u01/db3/tdata01.dbf
/u01/db3/tlarge01.dbf
6 rows selected.
Looks good from the DB side (ignore the UNDO datafile, this is CDB undo datafile, since PDB does not have its own). How does the storage usage look?
[root@cdbtest u01]# btrfs filesystem df /u01
Data: total=29.01GB, used=21.23GB
System, DUP: total=8.00MB, used=4.00KB
System: total=4.00MB, used=0.00
Metadata, DUP: total=1.00GB, used=124.87MB
Metadata: total=8.00MB, used=0.00
Still 21.23GB. Lets open both DB2 and DB3 and see what happens.
SQL> alter session set container=cdb$root;
Session altered.
SQL> alter pluggable database db2 close;
Pluggable database altered.
SQL> alter pluggable database db2 open;
Pluggable database altered.
SQL> alter pluggable database db3 open;
Pluggable database altered.
SQL> select name, open_mode, guid from v$pdbs;
NAME OPEN_MODE GUID
------------------------------ ---------- --------------------------------
PDB$SEED READ ONLY FFCDD773320B2767E0432700FA0A06D0
DB1 MOUNTED FFCC6C3F473E124BE0432700FA0A429E
DB2 READ WRITE 000A7D190B3C15A1E0532700FA0A3C10
DB3 READ WRITE 000C54AE44352331E0532700FA0AFA69
[root@cdbtest u01]# btrfs filesystem df /u01
Data: total=29.01GB, used=21.23GB
System, DUP: total=8.00MB, used=4.00KB
System: total=4.00MB, used=0.00
Metadata, DUP: total=1.00GB, used=124.90MB
Metadata: total=8.00MB, used=0.00
Still no additional storage used by the snapshot. I’ll modify some data in DB3 tables, then it must consume additional space.
SQL> alter session set container=db3;
Session altered.
SQL> select count(*) from t1.large;
COUNT(*)
----------
1897686
SQL> desc t1.large
Name Null? Type
----------------------------------------------------- -------- ------------------------------------
OWNER NOT NULL VARCHAR2(128)
OBJECT_NAME NOT NULL VARCHAR2(128)
SUBOBJECT_NAME VARCHAR2(128)
OBJECT_ID NOT NULL NUMBER
DATA_OBJECT_ID NUMBER
OBJECT_TYPE VARCHAR2(23)
CREATED NOT NULL DATE
LAST_DDL_TIME NOT NULL DATE
TIMESTAMP VARCHAR2(19)
STATUS VARCHAR2(7)
TEMPORARY VARCHAR2(1)
GENERATED VARCHAR2(1)
SECONDARY VARCHAR2(1)
NAMESPACE NOT NULL NUMBER
EDITION_NAME VARCHAR2(128)
SHARING VARCHAR2(13)
EDITIONABLE VARCHAR2(1)
ORACLE_MAINTAINED VARCHAR2(1)
SQL> update t1.large set owner = substr(owner, 1, 2);
1897686 rows updated.
SQL> commit;
Commit complete.
SQL> alter system checkpoint;
System altered.
SQL> select round(bytes/1024/1024) mb from dba_segments where owner='T1' and segment_name = 'LARGE';
MB
----------
256
[root@cdbtest u01]# btrfs filesystem df /u01
Data: total=29.01GB, used=21.78GB
System, DUP: total=8.00MB, used=4.00KB
System: total=4.00MB, used=0.00
Metadata, DUP: total=1.00GB, used=130.33MB
Metadata: total=8.00MB, used=0.00
I tried to change every block on that table. Table is 256MB and 21.78-21.23=0.55GB was changed on the disk. Just for a test, lets try the update again (just to see how BTRFS snapshots work a little).
SQL> update t1.large set owner = 'AX';
1897686 rows updated.
SQL> commit;
Commit complete.
SQL> alter system checkpoint;
System altered.
[root@cdbtest u01]# btrfs filesystem df /u01
Data: total=29.01GB, used=22.00GB
System, DUP: total=8.00MB, used=4.00KB
System: total=4.00MB, used=0.00
Metadata, DUP: total=1.00GB, used=132.34MB
Metadata: total=8.00MB, used=0.00
I should have modified the same blocks, but BTRFS used another 0.22GB of disk space. Need to look more into how BTRFS snapshots work. But here you have it, PDB snapshot cloning without restrictions 🙂