Identifing the Master node In RAC

In RAC, every data block is mastered by an instance. Mastering a block simply means that master instance keeps track of the state of the block until the next reconfiguration event.
– Remastering can be triggered as result of
    – Manually
    – Resource affinity
    – Instance crash
– Method – I gets info about master node from v$gcspfmaster_info   using data_object_id
– Method – II gets info about master node from v$dlm_ress and v$ges_enqueue   using resource name in hexadecimal format
– Method – III gets info about master node from x$kjbl with x$le using resource name in hexadecimal format
– CURRENT SCENARIO –
– 3 node setup
– name of the database – orcl
— SETUP –
SYS@NODE1>create table scott.emp1 as
             select * from scott.emp;
– Get data_object_id for scott.emp1
SQL> col owner for a10
col data_object_id for 9999999
col object_name for a15
select owner, data_object_id, object_name
from dba_objects
where owner = ‘SCOTT’
and object_name = ‘EMP1?;
OWNER      DATA_OBJECT_ID OBJECT_NAME
———- ————– —————
SCOTT               74652 EMP1

For Method-II and Method-III, we need to find out file_id and block_id and hence GCS  resource name in hexadecimal format

 — Get File_id and range of block_ids of emp1 table
– It can be seen that emp1 lies in block 523 of file 4.
SQL>select dbms_rowid.rowid_relative_fno(rowid) FILE_NO,
min(dbms_rowid.rowid_block_number(rowid)) MIN_BLOCK_ID,
max(dbms_rowid.rowid_block_number(rowid))  MAX_BLOCK_ID
from scott.emp1
group by dbms_rowid.rowid_relative_fno(rowid);

   FILE_NO MIN_BLOCK_ID MAX_BLOCK_ID
———- ———— ————
         4          523          523

– Find the GCS resource name to be used in  the query using blodk_id and data_object_id retrieved above.

   x$kjbl.kjblname = resource name in hexadecimal format([id1],[id2],[type]
   x$kjbl.kjblname2 = resource name in decimal format
   Hexname will be used to query resource master using v$dlm_ress , v$ges_enqueue, $kjbl
   and x$le

SQL> col hexname for a25
col resource_name for a15
select b.kjblname hexname, b.kjblname2 resource_name
from x$le a, x$kjbl b
where a.le_kjbl=b.kjbllockp
and a.le_addr = ( select le_addr
from x$bh
where dbablk = 524
and obj    = 74653
and class  = 1
and state   <> 3);

HEXNAME                   RESOURCE_NAME
————————- —————
[0x21b][0x4],[BL]         524,4,BL

– Manually master the EMP table to node2 –


SYS@NODE1>oradebug lkdebug -m pkey <objectid>

SYS@NODE1>oradebug lkdebug -m pkey 74653


—- GET RESOURCE MASTER NAME ———-


Method – I gets info about master node from v$gcspfmaster_info using data_object_id
– ——-
– Note that current master is node2 (Node numbering starts from 0)
SYS@node1>col object_name for A10
        select o.object_name, m.CURRENT_MASTER
from   dba_objects o, v$gcspfmaster_info m
where o.data_object_id=74653
and m.data_object_id = 74653 ;
OBJECT_NAM CURRENT_MASTER
———- ————–
EMP1                    1

—- Method II gets info about master node from v$dlm_ress and v$ges_enqueue using resource name in hexadecimal format
– check that master node is node2 (node numbering starts with 0)
SYS@NODE1>col resource_name for a22 select a.resource_name,  a.master_node
from   v$dlm_ress a, v$ges_enqueue b
where upper(a.resource_name) = upper(b.resource_name1)
and a.resource_name like ‘%[0x21b][0x4],[BL]%’;

RESOURCE_NAME          MASTER_NODE
———————- ———–
[0x20b][0x4],[BL]                1

Method – III gets info about master node from x$kjbl with x$le   using resource name in hexadecimal format
–  This SQL joins   x$kjbl with x$le to retrieve resource master for a block
– Note that current master is node2(MASTER=1)
SYS@NODE1> select kj.kjblname, kj.kjblname2, kj.kjblmaster master
from (select kjblname, kjblname2, kjblowner, kjblmaster, kjbllockp
from x$kjbl
where kjblname = ‘[0x21b][0x4],[BL]’
) kj, x$le le
where le.le_kjbl = kj.kjbllockp
order by le.le_addr;
KJBLNAME                       KJBLNAME2                          MASTER
—————————— —————————— ———-
[0x20b][0x4],[BL]              524,4,BL                                     1

  • December 30, 2017 | 17 views
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