Materialized Views Concepts – Discussion Series 2

We have seen Discussion Series 1 of materialized view concepts and we know how to create materialized view and also what each clause of Mview creation mean.

In this article we will see all backend tables that can be accessed to check the details of materialized view.

We will begin with identifying materialized view

DBA_SNAPSHOTS (On MView site)

Most important table for checking MView info is DBA_SNAPSHOTS.

We need to query this table on snapshot site (where MView is created)

SQL>select name, table_name, MASTER, MASTER_LINK, REFRESH_METHOD, UPDATABLE , LAST_REFRESH, STATUS, PREBUILT, REFRESH_MODE from dba_snapshots where name = 'T_REP';
NAME TABLE_NAME MASTER MASTER_LINK REFRESH_MET UPD LAST_REFRESH STATUS PRE REFRESH_
---------- ---------- -------------------- ------------------------------ ----------- --- ---------------- ------- --- --------
T_REP T_REP T @"DB1.AMAZON" PRIMARY KEY NO 2012-10-13:22:26 UNKNOWN YES DEMAND

DBA_REFRESH_CHILDREN (On Mview Site)

we can group multiple materialized views into a group and refresh all materialized view all at once.

This can be done by creating a refresh group.

You can see all steps to create refresh group at http://docs.oracle.com/cd/B28359_01/server.111/b28327/rarmviewgroup.htm

Once you create refresh group and add MView to it, you can see the info in MVIEW_REFRESH_GROUPS table

BEGIN
   DBMS_REFRESH.MAKE (
      name => 'TEST_REF_GROP',
      list => '', 
      next_date => SYSDATE, 
      interval => 'SYSDATE + 1/24');
END;
/

BEGIN
   DBMS_REFRESH.ADD (
      name => 'TEST_REF_GROP',
      list => 'T_REP',
lax => FALSE );
END;
/
SQL>select name, RNAME, REFGROUP, INTERVAL, TYPE from dba_refresh_children where name = 'T_REP';

NAME       RNAME REFGROUP INTERVAL TYPE
------------------------------ ------------------------------ ---------- ------------------------------ ------------------------------
T_REP       TEST_REF_GROP     3693 SYSDATE + 1/24 SNAPSHOT

SQL>

DBA_SNAPSHOT_LOGS (On Master site):

If we want to check information about MLOG table, we can view this table.

SQL>select master, LOG_TABLE, ROWIDS, PRIMARY_KEY, SNAPSHOT_ID, CURRENT_SNAPSHOTS from dba_snapshot_logs where master = 'T';
MASTER       LOG_TABLE       ROW PRI SNAPSHOT_ID CURRENT_SNAPSHOT
------------------------------ ------------------------------ --- --- ----------- ----------------
T       MLOG$_T       NO  YES     15119 2012-10-13:22:26

Since this is primary key based MLOG, we can see YES for primary key column. CURRENT_SNAPSHOT gives when was this last refreshed. This is same as LAST_REFRESH column in DBA_SNAPSHOTS

DBA_REGISTERED_SNAPSHOTS (On Master site):

To Check how many sites are registered for 1 master table, we can query DBA_REGISTERED_SNAPSHOTS

This table has a column called name which is basically the name of Mview on MVIEW site. Since each MVIEW site can have a different name we cannot compare this column to get list of sites registered for 1 master table.

But we don’t have any master column in this table so we join this table with DBA_SNAPSHOT_LOGS to get list of sites which are registered for a master table

SQL>select a.master, b.name, b.snapshot_site from dba_snapshot_logs a, dba_registered_snapshots b
  2  where a.snapshot_id = b.snapshot_id
  3  and a.master = 'T';

MASTER       NAME       SNAPSHOT_SITE
------------------------------ ------------------------------ ------------------------------
T       T_REP       DB1.AMAZON

To check which snapshots has delay

We can use following query to check which snapshots has refresh delay in mins

select a.master, b.name, b.snapshot_site, (sysdate - a.CURRENT_SNAPSHOTS)*24*60 "delay Mins"
from dba_snapshot_logs a, dba_registered_snapshots b
where a.snapshot_id = b.snapshot_id
and (sysdate - a.CURRENT_SNAPSHOTS)*24*60 > &delay;

This will ask for delay and you can enter delay in mins.

After that this will list down all snapshots which are having delay more than what you entered.

Example, if you want to list down all snapshots having delay of more than 10 mins, you need to enter 10.

x$knstmvr

This is another internal table which can be used to check the progress of snapshots.

Columns in this table is self understood.

Following query will provide you the details of snapshot progress

column mvowner format a10 
Column mvname format a30 
column refmode format a8 
column refstate format a12 
column inserts format 99999999 
column updates format 999999999 
column deletes format 999999999 
column event format a30 
column spid format a6 
select  currmvowner_knstmvr mvowner, 
currmvname_knstmvr mvname, 
decode( reftype_knstmvr, 0, 'FAST', 1, 'FAST', 2, 'COMPLETE', REFTYPE_KNSTMVR ) refmode, 
decode(groupstate_knstmvr, 1, 'SETUP', 2, 'INSTANTIATE',3, 'WRAPUP', 'UNKNOWN' ) refstate, 
total_inserts_knstmvr inserts, 
total_updates_knstmvr updates, 
total_deletes_knstmvr deletes, 
b.spid,c.event 
from x$knstmvr X, v$session a, v$process b, v$session_wait c 
WHERE type_knst=6 
and a.paddr = b.addr 
and a.sid = c.sid 
and x.SID_KNST = a.sid 
and x.SERIAL_KNST = a.serial#;

In the next article about MView discussion series we will discuss about MLOG table and some internal details about fast refresh and how it works.

Hope this helps !!

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