SAN Migration and moving files with ASM

Here’s a quick post to help with LUN, SAN or File migration when using Oracle ASM.

Please note that this is just an example method, and is not a definitive guide.
You need to ensure your approach is appropriate for your environment.

Did you know that you can add and drop disks on a diskgroup in a single command.
This saves Oracle from doing 2 REBAL actions and speeds things up considerably using a lot fewer resources.

sqlplus / as sysasm;

> ALTER DISKGROUP data 
2   ADD  DISK 'ORCL:disk101','ORCL:disk102' 
3   DROP DISK 'disk042'     ,'disk043' 
4   REBALANCE POWER n;

Diskgroup altered.

You can monitor the REBAL operation:

select * from v$asm_operation;

GROUP_NUMBER OPERA PASS      STAT POWER ACTUAL SOFAR EST_WORK EST_RATE EST_MINUTES ERROR_CODE CON_ID
------------ ----- --------- ---- ----- ------ ----- -------- -------- ----------- ---------- ------
           6 REBAL REBALANCE  RUN     1      1    68    20397     3030           8                 0
           6 REBAL COMPAT    WAIT     1      1     0        0        0           0                 0

If you are just migrating from one SAN to another, without needing to move files between diskgroups, this is a really easy way to achieve it.

From Oracle 12.1 onwards. if you are moving Datafiles from one Diskgroup to a new Diskgroup, that’s straightforward too:

export ORACLE_SID=ORCL
sqlplus  / as sysdba

alter database move datafile '+DATA_DG/ORCL/DATAFILE/system.101.902468275' to '+NEW_DG';

Moving logfiles involves a drop and re-create, but it still fully online.
Take care if using DataGuard that you do not try to drop logfiles before they are archived and applied to the standby:

alter database  add logfile member '+NEW_DG' to group 1;
alter database drop logfile member '+DATA_DG/ORCL/ONLINELOG/group_1.102.902049284';

Moving tempfiles can be tricky. The default gets used really quickly after startup.

You need to add a tempfile and then get all processes to not be using the old tempfile before you can drop it [select * from gv$sort_usage]. Worst-case, this may involve a SHUTDOWN, then a STARTUP RESTRICT to stop processes connecting. Alternatively, create a new default TEMP tablespace and convince processes to use that one.

alter tablespace temp add  tempfile '+NEW_DG';
alter tablespace temp drop tempfile '+DATA_DG/ORCL/TEMPFILE/temp.204.992482742';

Moving controlfiles requires a stop and start of the database. There’s no on-line options here. I tend to do the following:

srvctl stop database -d ORCL

sqlplus / as sysdba
startup nomount
show parameter control_files


rman target /
restore controlfile to '+NEW_DG' from '+DATA_DG/ORCL/CONTROLFILE/current.291.939274434';

sqlplus / as sysdba
alter system set control_files='+NEW_DG/ORCL/CONTROLFILE/current.992.346677889'
                              ,'+FRA_DG/ORCL/CONTROLFILE/current.???.?????????'
                               scope=spfile sid='*';
shutdown

srvctl start database -d ORCL

To move your spfile in ASM is a 2-stage process which will automatically update your database config in grid control:

sqlplus / as sysdba
create  pfile='/tmp/ORCL.ora' from spfile;
create spfile='+NEW_DG'       from pfile='/tmp/ORCL.ora';

Moving a password file in ASM is straightforward too:
NOTE: you are not allowed to move OMF files names and you must copy files via their alias.

as grid:
asmcmd
cp +DATA_DG/ORCL/orapworcl +NEW_DG/ORCL/orapworclexit
as oracle:
srvctl modify database -d ORCL -pwfile +NEW_DG/ORCL/orapworclsrvctl config database -d ORCL | grep Password

If you are using Block Change Tracking, you may need to move that file too:

alter database disable block change tracking;
alter database enable block change tracking using file '+NEW_DG';

Finally, if you’re dropping disk groups don’t forget to modify the disk group dependencies in Grid Infra so your DB isn’t dependent upon groups you have now removed:

srvctl config datbase -d ORCL | grep Group
srvctl modify database -d ORCL -diskgroup 'NEW_DG,FRA_DG,other_DG'

I hope you found this quick guide useful.

Primarys Keys and their supporting indexes

Sometimes things just happen which makes you realise that stuff you thought all experienced DBA’s knew about isn’t common knowledge. I suppose it’s a side effect of working with the same evolving product for over 25 years at dozens of clients, when the colleague you are talking to has a mere decade of experience at fewer companies (and therefore less diversity of challenge).

Today I noticed that a release was creating a table, then an index, and then adding a Primary Key based upon the index. Pretty normal, but the indexes were non-unique. Interesting. Is that valid? (yes) It is sensible? (under some circumstances, also yes). Is it wrong but nobody noticed until it got to me? Probably.

However, there’s more variables at play here than first meets the eye. The Primary Key is being enforced by a pre-existing non-unique index, rather than create its own index “dynamically” (which would be unique under most circumstances). So therefore we have a few questions to answer

  1. Is the index being used optimal?
  2. How do I know it’s using a pre-created index and the constraint did not create its own index?
  3. What happens if I drop the PK constraint?

 

Scenario 1: create table, create constraint

You get a nice neat fast index enforcing the constraint. If you drop the constraint, the index will also get removed. This may or may not be what you want. You may need to put a new index back on the table…

Scenario 2: create table, create unique index, create constraint

You get a nice neat fast index enforcing the constraint. If you drop the constraint, the index does not get removed. This may or may not be what you want. The index which was left behind might cause a problem if you miss the fact it’s still around…

Scenario 3: create table, create non-unique index (same as constraint columns), create constraint

The index enforcing the constraint is slightly less efficient enforcing the constraint as it has to optimize to an index range scan, not a unique scan. However, if you drop the constraint you still have a non-unique index. This may be a very useful ability for bulk data loads with questionable data, although the use-cases are limited and tend to be Warehouse-centric.

If you have a deferrable constraint, you must have a non-unique index to enforce the constraint as there may temporarily be duplicate keys in the table part-way through the transaction.

Scenario 4: create table, create non-unique composite index, create constraint which uses leading columns of that index but not all of the columns

The index may be somewhat less efficient enforcing the constraint by having less rows per block and possibly more levels, but this inefficiency may help overall system efficiency by having to maintain less indexes – maintaining 2 indexes instead of 1 is a 100% overhead in index maintenance. The composite index cannot be a unique index.

 

Some worked example showing the above scenarios (ran on Oracle 12.1.0.2.0 in a PDB) :

NEIL @ ORCL01 > -- Scenario 1
NEIL @ ORCL01 > drop table neil;
Table dropped.
NEIL @ ORCL01 > create table neil (col_id number, col_txt varchar2(10 char));
Table created.
NEIL @ ORCL01 > alter table neil add constraint neil_pk primary key (col_id) ;
Table altered.
NEIL @ ORCL01 > select index_name,uniqueness from user_indexes where table_name = 'NEIL';
INDEX_NAME           UNIQUENESS
-------------------- --------------------
NEIL_PK              UNIQUE
NEIL @ ORCL01 > insert into neil values (1,'A');
1 row created.
NEIL @ ORCL01 > insert into neil values (1,'B');
insert into neil values (1,'B')
*
ERROR at line 1:
ORA-00001: unique constraint (NEIL.NEIL_PK) violated
NEIL @ ORCL01 > commit;
Commit complete.
NEIL @ ORCL01 > alter table neil drop constraint neil_pk;
Table altered.
NEIL @ ORCL01 > -- And the index is gone...
NEIL @ ORCL01 > select index_name,uniqueness from user_indexes where table_name = 'NEIL';
no rows selected
NEIL @ ORCL01 > -- Scenario 2
NEIL @ ORCL01 > drop table neil;
Table dropped.
NEIL @ ORCL01 > create table neil (col_id number, col_txt varchar2(10 char));
Table created.
NEIL @ ORCL01 > create unique index neil_i on neil(col_id);
Index created.
NEIL @ ORCL01 > alter table neil add constraint neil_pk primary key (col_id) ;
Table altered.
NEIL @ ORCL01 > select index_name,uniqueness from user_indexes where table_name = 'NEIL';
INDEX_NAME           UNIQUENESS
-------------------- --------------------
NEIL_I               UNIQUE
NEIL @ ORCL01 > insert into neil values (1,'A');
1 row created.
NEIL @ ORCL01 > insert into neil values (1,'B');
insert into neil values (1,'B')
*
ERROR at line 1:
ORA-00001: unique constraint (NEIL.NEIL_PK) violated
NEIL @ ORCL01 > commit;
Commit complete.
NEIL @ ORCL01 > alter table neil drop constraint neil_pk;
Table altered.
NEIL @ ORCL01 > -- And the index survives
NEIL @ ORCL01 > select index_name,uniqueness from user_indexes where table_name = 'NEIL';
INDEX_NAME           UNIQUENESS
-------------------- --------------------
NEIL_I               UNIQUE
NEIL @ ORCL01 > -- Scenario 3
NEIL @ ORCL01 > drop table neil;
Table dropped.
NEIL @ ORCL01 > create table neil (col_id number, col_txt varchar2(10 char));
Table created.
NEIL @ ORCL01 > create index neil_i on neil(col_id);
Index created.
NEIL @ ORCL01 > alter table neil add constraint neil_pk primary key (col_id) using index neil_i;
Table altered.
NEIL @ ORCL01 > select index_name,uniqueness from user_indexes where table_name = 'NEIL';
INDEX_NAME           UNIQUENESS
-------------------- --------------------
NEIL_I               NONUNIQUE
NEIL @ ORCL01 > insert into neil values (1,'A');
1 row created.
NEIL @ ORCL01 > insert into neil values (1,'B');
insert into neil values (1,'B')
*
ERROR at line 1:
ORA-00001: unique constraint (NEIL.NEIL_PK) violated
NEIL @ ORCL01 > commit;
Commit complete.
NEIL @ ORCL01 > alter table neil drop constraint neil_pk;
Table altered.
NEIL @ ORCL01 > -- And the index survives
NEIL @ ORCL01 > select index_name,uniqueness from user_indexes where table_name = 'NEIL';
INDEX_NAME           UNIQUENESS
-------------------- --------------------
NEIL_I               NONUNIQUE
NEIL @ ORCL01 > -- Scenario 4
NEIL @ ORCL01 > drop table neil;
Table dropped.
NEIL @ ORCL01 > create table neil (col_id number, col_txt varchar2(10 char));
Table created.
NEIL @ ORCL01 > create index neil_i_composite on neil(col_id,col_txt);
Index created.
NEIL @ ORCL01 > alter table neil add constraint neil_pk primary key (col_id) using index neil_i_composite;
Table altered.
NEIL @ ORCL01 > select index_name,uniqueness from user_indexes where table_name = 'NEIL';
INDEX_NAME           UNIQUENESS
-------------------- --------------------
NEIL_I_COMPOSITE     NONUNIQUE
NEIL @ ORCL01 > insert into neil values (1,'A');
1 row created.
NEIL @ ORCL01 > insert into neil values (1,'B');
insert into neil values (1,'B')
*
ERROR at line 1:
ORA-00001: unique constraint (NEIL.NEIL_PK) violated
NEIL @ ORCL01 > commit;
Commit complete.
NEIL @ ORCL01 > alter table neil drop constraint neil_pk;
Table altered.
NEIL @ ORCL01 > -- And the index survives
NEIL @ ORCL01 > select index_name,uniqueness from user_indexes where table_name = 'NEIL';
INDEX_NAME           UNIQUENESS
-------------------- --------------------
NEIL_I_COMPOSITE     NONUNIQUE

So how do I tell if, when I drop my constraint, I will also drop the index? This does not appear to be exposed in any DBA_ view of which I am aware, so I have had to rely upon this post from Jonathan Lewis to help me decipher the information. You need to see if certain bits are set in the column sys.ind$.property. Here’s my worked example to show the information we seek:

NEIL @ ORCL01 > drop table neil_cons_create;
Table dropped.
NEIL @ ORCL01 > create table neil_cons_create (col_id number, col_txt varchar2(10 char));
Table created.
NEIL @ ORCL01 > alter table neil_cons_create add constraint neil_cons_create_pk primary key (col_id);
Table altered.
NEIL @ ORCL01 > drop table neil_pre_create;
Table dropped.
NEIL @ ORCL01 > create table neil_pre_create (col_id number, col_txt varchar2(10 char));
Table created.
NEIL @ ORCL01 > create unique index neil_pre_create_i on neil_pre_create(col_id);
Index created.
NEIL @ ORCL01 > alter table neil_pre_create add constraint neil_pre_create_pk primary key (col_id);
Table altered.
NEIL @ ORCL01 > select index_name,uniqueness from user_indexes where table_name like 'NEIL%';
INDEX_NAME           UNIQUENESS
-------------------- --------------------
NEIL_CONS_CREATE_PK  UNIQUE
NEIL_PRE_CREATE_I    UNIQUE

select do.owner,do.object_name,do.object_id,ind.property, 'Keep Index' action
  from sys.ind$ ind
       ,dba_objects do
where do.object_name like 'NEIL%'
  and do.object_id = ind.obj#
  and bitand(ind.property,4097) = 4097
union all
select do.owner,do.object_name,do.object_id,ind.property, 'Drop Index' action
  from sys.ind$ ind
      ,dba_objects do
where do.object_name like 'NEIL%'
  and do.object_id = ind.obj#
  and bitand(ind.property,4097) <> 4097
order by 1,2,3
/
OWNER        OBJECT_NAME         OBJECT_ID  PROPERTY   ACTION
------------ ------------------- ---------- ---------- --------------------
NEIL         NEIL_CONS_CREATE_PK      93814       4097 Keep Index
NEIL         NEIL_PRE_CREATE_I        93816          1 Drop Index
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