Will Materialized view log reduces the performance of DML statements on the master table

Hi all,
I need to refresh a on demand fast refresh Materialized view in Oracle 11GR2. For this purpose I created a Materialized view log on the table (Non partitioned) in which records will be inserted @ rate of 5000/day as follows.
CREATE MATERIALIZED VIEW LOG ON NOTES NOLOGGING WITH PRIMARY KEY INCLUDING NEW VALUES;
This table already has 20L records and adding this Mview log will reduce the DML performance on the table ?
Please guide me on this.

Having the base table maintain a materialised view log will have an impact on the speed of DML statements - they are doing extra work, which will take extra time. A more sensible question would be to ask whether it will have a significant impact, to which the answer is almost certainly "no".
5000 records inserted a day is nothing. Adding a view log to the heap really shouldn't cause any trouble at all - but ultimately only your own testing can establish that.

Similar Messages

Materialized View Logs on OLTP DB- Performance issues

Hi All,
We have a request to check what would be the performance impact of having Matirialized View (with FAST refresh each 5 and each 30 min).
We have been using some APIs( I don't have full details of this job) to refresh tables in Reportign DB and want to switch to MVIEWS in the next release.
The base tables for this MVs are in DB1 with high DML activity.
We are planing to create 7 MVs on a reporting DB pointing to the corresponding tables in DB1.
I am setting up the env with the required tables to test this and also want to know your experiences in implementing Mviews with Fast refresh pointing to a typical OLTP DB as I am new to MVIEWS.
How it affects the performance of DML statements on base tables?
How often you had to do complete refresh because of invalid/outdated Mview Logs?
other Maintenance overheads?
any possible workarounds?
Oracle Version: 9.2.0.8
OS : HP-UX
Thank you for sharing your experiences.

Doing incremental refreshes every 5 minutes willadd some amount of load to the OLTP system. Again,
depending on your environment, that may or may not be
significant.
what factors can effet this? Among other things, the size of the materialized view logs that need to be read, which in turn depends on the number of transactions and the setup of the materialized views, the current load on the OLTP system, etc. If you're struggling with an I/O or CPU bottleneck at peak processing now, for example, having a dozen materialized view refresh processes running as well would probably generate noticable delays in the system. If you have plenty of spare CPU & I/O bandwidth, the refreshes will be less noticable.
is it the same in 10g R2 too? we are upgrading to the
same in coming October.Streams is far easier to deal with in 10.2.
Justin

Materialized View Log table with sequence

I have a materialized view log in Database A..a very simple one...similar to "create materialized view log on t WITH PRIMARY KEY"...The primary key is a composite key of 2 columns...Description of the mlog table looks like this...
desc mlog$_t
emp_ctr NUMBER
emp_date DATE
SNAPTIME$$ DATE
DMLTYPE$$ VARCHAR2(1)
OLD_NEW$$ VARCHAR2(1)
CHANGE_VECTOR$$ RAW(255)
The Materialized view is in database B...again a simple one...no aggregation...This gets refreshed on demand manually evey week. The records that get accumulated in the MLOG every week is ~ 300K..The manual refresh used to finish in about 20mins but since last week it is running for ever. Upon reviewing the contents of MLOG I noticed that it contained a mixture of inserts and updates. I'm not sure if the MLOG contanied only inserts in the past when the MV used to refresh very quickly...Based on the documentation, Oracle recommends creating MLOGS with "sequence" whenever inserts/updates/deleted are expected. I'm planning to drop and recreate the MLOG with sequence with the hope that this would fix the slow refresh issue...Appreciate if you could let me know your thoughs...
I'm also planning to trace the session to get some wait event statistics to find out the reason for the slow refresh...

There are a few reasons why refreshes slow down over time.
1. Is the log table being cleared out after a refresh? If not, you may have another mview (maybe even one that doesn't exist any more) registered against this log. When this happens, the log table never stops growing.
2. How big is the segment occupied by the table? If it has grown very large at some time in the past (e.g., because refresh was delayed), then when the refresh does a FTS on the log it will scan the whole segment - even if only a few rows are present.
3. It may help to add an index to the PK columns, and another to SNAPTIME$$. Without them, the refresh will FTS the log. For a big segment, that can take a long time.
-- Phil

Query on Materialized view and materialized view log

I am creating a materialized view something like this.but getting following error:
ERROR at line 1:
ORA-12032: cannot use rowid column from materialized view log on "SCOTT"."EMP"
SQL> create snapshot log on scott.emp;
Materialized view log created.
SQL> create materialized view scott_emp refresh fast on demand as select deptno,sum(sal) sum_sal from scott.emp group by deptno;
ERROR at line 1:
ORA-12032: cannot use rowid column from materialized view log on "SCOTT"."EMP"
Note when i have my query in materialized view as "select * from emp;" in place of
"select deptno,sum(sal) sum_sal from scott.emp group by deptno;" This code works fine.
How do i have a materialized with with a group by clause.
Thanks in Advance

Got the answer myself.
I wasnt adding all the required columns.
CREATE MATERIALIZED VIEW LOG ON scott.emp
WITH SEQUENCE, ROWID (<all the required columns>)
INCLUDING NEW VALUES;
Anyways,
Thanks guys...

ORA-12096: error in materialized view log on a table

Hi while updating a table getting below error
ORA-12096: error in materialized view log on "FII"."FII_GL_JE_SUMMARY_B"
What might be the problem.
Thanks.

might be table definition has changed, you may need to drop the mview log and recreate it.

Performance consequences to adding materialized view logs to tables?

I am writing a very complex query for a client of our transactional database system and this will require the creation of a materialized viewbecause all attempts at tuning to make performance acceptable have failed.
I want to enable fast refresh of the MVIEW but I am confused regarding the consequences of the addition of adding materialized view logs to the base tables.
Some of the tables are large and involved in alot of transactions and I am wondering if the performance of INSERT/UPDATES will be seriously affected by the presence of an mview log.
This may be a simple question to answer but I was unable to find a clear cut answer in the literature.
Thanks for any answers!!
Chris Mills
Biotechnology Data Management Consultant

Last time i looked into this there were three cases to consider
If you're doing conventional row-by-row DML then the impact is just one insert into a heap table per row modified.
If you are modifying a high number of rows using bulk-binds then the overhead is very severe because modifying 1,000 rows on the base table causes 1,000 non-bulk bound inserts into the log table.
Direct path inserts have extremely low overhead because the MV log is not touched. Instead, the range of new rowids added is logged in ALL_SUMDELTA
http://oraclesponge.wordpress.com/2005/09/15/optimizing-materialized-views-part-ii-the-direct-path-insert-enhancement/

Creating a Materialized View Log After the Data has been instered

Hi,
I am trying to create a method of replication from Oracle to MySQL using the Materialized View Log table.
This has been done before and works quite well, the only problem is that I am trying to impliment the log after the table has been created and populated and wish to push all the existing data through the log file...
Does anyone know if it is possible to refresh the Materialized View Log and not a Materialized View.
The way the replication is intended to work is:
Oracle> Data inserted into table
Oracle> writes the vector data to the MVL
Script> Monitors the MVL and can see the changes being made to the Oracle Table
Script> Updates MySQL with the data and removes the rows from the MVL
MySQL is then used with other unix systems
Currently we export the data from the table using Triggers and a cronjob running every x minute to check for changes in the TriggerTables
Many thanks for your time on this, I have been checking for almost a whole working day and not found the answer to this problem.

Thats what I thought, the MVL will only read data that has changed since it was created and wont have the option to load in all the data as though it was made before the table was created.
From what I have read, the MVL is quicker than a Trigger and I have some free code that prooved to work from a MVL using it as a reference to know what records to update. There is not that much to a MVL, a record ID and type of update, New, Update or Delete.
I think what I will have to do is work on a the same principle for the MVL but use a Trigger as this way we can do a full reload if required at any point.
Many thanks for your help.

Whats the purpose of materialized view log?whats create view log with rowi

Why we create materialized view log ?????whats the use???
what do you mean by "create view log with rowid"
Regards
Gagan

A materialized view log stores the change vectors made to a particular table in order to allow materialized views that reference that table to be incrementally refreshed rather than re-materializing the data every time. It's a much more efficient way to refresh a materialized view.
WITH ROWID specifies that the materialized view log should store the ROWID of a row with the change vector, which is one way of identifying which row(s) in the materialized view should be updated by which change vector. You can also use the primary key value for this.
Justin

How to CREATE MATERIALIZED VIEW LOG (MV fast refresh) with some JOINS

Hi @ all,
i'm trying to create a MATERIALIZED VIEW LOG for a fast refresh of a MATERIALIZED VIEW.
It works fine with a simple Request in the MATERIALIZED VIEW:
CREATE MATERIALIZED VIEW MV_ZOTD43_P
TABLESPACE GDII
BUILD IMMEDIATE
REFRESH FORCE AS
SELECT * FROM ZOTD43_P;
COMMIT;
CREATE MATERIALIZED VIEW LOG ON ZOTD43_P
TABLESPACE "GDII"
WITH PRIMARY KEY, ROWID, SEQUENCE INCLUDING NEW VALUES;
call DBMS_MVIEW.REFRESH('MV_ZOTD43_P', 'f');
But when I use a complex SQL-Request with some JOINS (one of the Table with spatial Data) in the MATERIALIZED VIEW, I get an error:
CREATE MATERIALIZED VIEW MV_TEST
TABLESPACE GDII
BUILD IMMEDIATE
REFRESH FORCE AS
SELECT lptd04_p.sst_nr AS sst_nr,
lptd03_p.aaaa AS aaaa,
lptd04_geom.geom as geom
FROM lptd04_p lptd04_p
JOIN lptd01_p lptd01_p ON lptd01_p.cre_nr = lptd04_p.sst_nr
JOIN lptd04_geom ON lptd04_geom.sst_nr = lptd04_p.sst_nr
JOIN lptd03_p lptd03_p ON lptd03_p.lief_nr = lptd04_p.lief_nr;
COMMIT;
CREATE MATERIALIZED VIEW LOG ON LPTD04_P
TABLESPACE "GDII"
WITH PRIMARY KEY, ROWID, SEQUENCE INCLUDING NEW VALUES;
call DBMS_MVIEW.REFRESH('MV_TEST', 'f');
Error report:
SQL Error: ORA-12004: REFRESH FAST kann für Materialized View "GDI"."MV_GDI_SST_STAMM" nicht benutzt werden
ORA-06512: in "SYS.DBMS_SNAPSHOT", Zeile 2255
ORA-06512: in "SYS.DBMS_SNAPSHOT", Zeile 2461
ORA-06512: in "SYS.DBMS_SNAPSHOT", Zeile 2430
ORA-06512: in Zeile 1
12004. 00000 - "REFRESH FAST cannot be used for materialized view \"%s\".\"%s\""
*Cause: The materialized view log does not exist or cannot be used. PCT
refresh is also not enabled on the materialized view
*Action: Use just REFRESH, which will reinstantiate the entire table.
If a materialized view log exists and the form of the materialized
view allows the use of a materialized view log or PCT refresh is
possible after a given set of changes, REFRESH FAST will
be available starting the next time the materialized view is
refreshed.
Am I doing something wrong or is it not possible CREATE MATERIALIZED VIEW LOG when the MATERIALIZED VIEW got some JOINS?
Regards,
Greq

Thanks for the link Alessandro ,
the error seems something to do with the Column-Type SDO_GEOMETRY, so
i create a new thread in the Spatial Discussion forum:
FAST REFRESHing of Oracle Materialized Views containing SDO_GEOMETRY column
Regards,
Greq

Creation of Materialized view and Materialized view log.

I wanted to create materialized view with 'REFRESH FAST ON COMMIT' option.
1) Table1 --it is partitioned range + list -- Added primary key
2) view1   -- having primary keys on view's base table
Steps:
1) create materialized view log on Table1 ; -- default primary key
2) create materialized view log on view1. --- It is giving below error.
ORA-00942: table or view does not exist
i wanted to create Materialized view like below
create materialized view
REFRESH fast ON commit
as
select ...
... from table1
where c1 in (select c1 from view1 where ... );
Question:
1) As i am getting above error while creating MV log on view. Can we create MV log on view or we have to create MV log on view base table?
2) To create MV with ''REFRESH FAST ON COMMIT' option , do we need to have primary key on master tables?
Any pointers on this will really helpful.
Thanks
Prasad

Also created MV LOG on 3 tables and tried with joins ..
create materialized view
REFRESH fast ON commit
as
select ...
... from table1 , tab2 t2,tab3 t3
where ....
and ...
Get same error ORA-12052: cannot fast refresh materialized view AVSYS.EVENT_LOG_MV
2052. 00000 - "cannot fast refresh materialized view %s.%s"
*Cause:    Either ROWIDs of certain tables were missing in the definition or
           the inner table of an outer join did not have UNIQUE constraints on
           join columns.
*Action:   Specify the FORCE or COMPLETE option. If this error is got
           during creation, the materialized view definition may have be
           changed. Refer to the documentation on materialized views.

Can't update master table when creating a materialized view log.

Hi all,
I am facing a very strange issue when trying to update a table on which I have created a materialized view log (to enable downstream fast refresh of MV's). The database I am working on is 10.2.0.4. Here is my issue:
1. I can successfully update (via merge) a dimension table, call it TABLEA, with 100k updates. However when I create a materialized view log on TABLEA the merge statement hangs (I killed the query after leaving it to run for 8 hrs!). TABLEA has 11m records and has a number of indexes (bitmaps and btree) and constraints on it.
2. I then create a copy of TABLEA, call it TABLEB and re-created all the indexes and constraints that exist on TABLEA. I created a materialzied view log on TABLEB and ran the same update....the merge completed in under 5min!
The only difference between TABLEA and TABLEB is that the dimension TABLEA is referenced by a number of FACT tables (by FKs on the FACTS) however this surely should not cause a problem. I don't understand why the merge on TABLEA is not completing...even though it works fine on its copy TABLEB? I have tried rebuilding the indexes on TABLEA but this did not work.
Any help or ideas on this would be most appreciated.
Kind Regards
Mitesh
email: [email protected]

Thats what I thought, the MVL will only read data that has changed since it was created and wont have the option to load in all the data as though it was made before the table was created.
From what I have read, the MVL is quicker than a Trigger and I have some free code that prooved to work from a MVL using it as a reference to know what records to update. There is not that much to a MVL, a record ID and type of update, New, Update or Delete.
I think what I will have to do is work on a the same principle for the MVL but use a Trigger as this way we can do a full reload if required at any point.
Many thanks for your help.

Truncate table and materialized view log

I user oracle 10 R2
I have a table and on that table a materialized view log.
I execute in a pl/sql procedure:
1) execute immediate('drop materialized view log on tab1');
then:
2) execute immediate('truncate table tab1');
3) Now I insert a lot of records in tab1
4) execute immediate('create materialized view log on tab1 WITH rowid INCLUDING NEW VALUES');
When I create the materialized view log I recieved this message:
ora32321: refresh fast on tab2 unsupported after detail table truncate
Why?

Refresh fast after truncate operation on container table is not supported, regardless the container table is or is not partitioned.
Perform a refresh complete.
ORA-32321 :
Cause:     A detail table has been truncated and no materialized view
     supports fast refersh after a detail table has been truncated
Action:     Use REFRESH COMPLETE. Note: you can determine why your
     materialized view does not support fast refresh after TRUNCATE
     using the DBMS_MVIEW.EXPLAIN_MV() API.

MATERIALIZED VIEW and MATERIALIZED VIEW LOG

Hello,
I have the following table
create table My_price
(price_id number(10),
product_id number(10),
price_date date,
price_value number(10,2));
I want to create the following materialized view
create materialized view Last_Price_Date
refresh
on commit complete
as
select max(price_date) as max_date, product_id from my_price group by product_id;
Do I have to create materialized view log ? Will my materialized view be refresh on commit without materialized view log ?

As a student the requisite first task is always to study. Thus your assignment is to go to http://tahiti.oracle.com and read the concept and architecture docs on Materialized Views so that you can learn about the different types of MVs and how and when they are refreshed. There you will learn about what ON COMMIT means.
Then please turn your "I want to create" into an "I created it." Then, having read the docs, you will be able to observe how your MV behaves.
PS: Your SELECT statement is not syntactically correct. Start by fixing it so that it works in SQL*Plus.

Materialized view logs for Fast refreshes

Hi,
I created MV and MV logs on the base table/main table. I set the base table in NOLOGGING MODE. so ofcourse redo is not gonna generate during DML but i wanted to know that:
Will NOLOGGING effect the MV logs for fast refreshes?
I came up on conclusion that MV logs are nothing to do with Redo Logs and would have no impact on MV logs for fast refresh since i have set my all base table in NOLOGGING MODE.
Looking forward for expert opinion.
REGARDS,

Though I'm not an expert...
SQL> alter table emp nologging;
Table altered.
SQL> create materialized view log on emp;
Materialized view log created.
SQL> select * from tab;
TNAME TABTYPE CLUSTERID
EMP TABLE
BONUS TABLE
SALGRADE TABLE
RUPD$_EMP TABLE
MLOG$_EMP TABLE
SQL> insert into emp values(1000,'Matt','Test',100,sysdate,1000,1000,10,11,11);
1 row created.
SQL> select *From mlog$_emp;
EMPNO SNAPTIME$ D O
CHANGE_VECTOR$$
1000 01-JAN-00 I N
FEFF

Materialized View Logs

Hi, I need some help understanding MV Logs. The information I find on MV Logs, is very basic, ie. the general syntax of creating a log, the types of logs, how they are refreshed etc.
Let me put my question this way. I want to create an MV, with a where clause that joins 3 tables. This should be simple enough. But how does the LOG(s) work ? Is there an MV Log for each table in the where-clause of the select statement ?
And, is there only 1 way of creating an MV Log? CREATE MATERIALIZED VIEW LOG ON mis.prov_cat_link with .......
Can't I specify the columns I want to "log" ? What if the select statement in my MV create statement only selects certain columns, and not all ? Maybe if I understand how the log works, I will understand the logic behind it, and how to create it.
I hope the above makes sense !

Using the WITH clause you can provide filter columns that are stored in the MV log.
Mike

Will Materialized view log reduces the performance of DML statements on the master table

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