Re: Refresh option for Materialized view , want to use it during refresh - for

David,

Glad to be of help.

Looking at your list of steps, I see that your questions is whether building an MV on the table T is beneficial. Tables and MVs, on prebuilt table or not, are stored as segments in the database; so space-sise there is no difference, nor there is any change in the way the MV/Table is accessed.

There are a few situations where you may want to convert a table to MV. They are:

• Building an MV enables Query Rewrite, where Oracle smartly decides to rewrite a user query to select from the MV instead of the main tables. This is not possible on a regular table. The user must explicitly select from it.
• If you want to refresh FAST, then MVs are required. You can do a fast refresh on a table, but you have to write your own procedures for that. DBMS_MVIEW package does it for you on MVs.
• Your designer software will recognize MV as one and will report it to all users, who are aware of the fact that it's an MV, useful for queries. A mere table will not be clear on that regard.

Converting a table to MV does not cost any resource, as the change is done inside the data dictionary only. So, if you are in doubt, you may just convert the table to MV anyway.

HTH. Arup Nanda

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Tuesday, October 28, 2003 12:04 PM refresh - for

> Arup,
>
> I really appreciate your answer in great details. I got "on prebuilt
table"
> work. Thanks a lot for your help. Here is another question:
>
> Do you see any advantage to use materialized view on prebuilt table for my
> data loading over just simple renaming tables as steps below:
>
> 1. create table t that is always accessed by applications
> 2. create table t1 that is a temp table for loading
> 3. load data into table t1
> 4. rename table t to table t2
> 5. rename table t1 to t
> 6. rename table t2 to t1
> 7. truncate table t1 for next day loading
>
> David
>
>
> >From: "Arup Nanda" <orarup_at_hotmail.com>
> >Reply-To: ORACLE-L_at_fatcity.com
> >To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> >Subject: Re: Refresh option for Materialized view , want to use it during
> >refresh - for
> >Date: Fri, 24 Oct 2003 18:04:33 -0800
> >
> >David,
> >
> >Answers to your questions:
> >
> >(1) Without knowing your exact needs, I wil offer a few different
> >scenarios.
> >I am assuming that you are doing a complete refresh every time. The
> >following pertain to that.
> >
> >Say, your name of the MV is MV1. Here are the steps the first time.
> >
> >1. Create table MV1
> >2. Create MV MV1 on that table.
> >
> >When you want to refresh complete:
> >
> >1. Create table MV1_TEMP. Choose a suitable method: CTAS across dblink
> >(with
> >NOLOGGING), SQL*Loader, Direct Load Insert, or simpley exp/imp.
> >2. Drop MV MV1. This drops the MV but doesn't drop the table.
> >3. Drop table MV1.
> >4. Rename table MV1_TEMP to MV1.
> >5. Recreate MV MV1.
> >6. Allow users to proceed as usual.
> >
> >Note the time consumed between Steps 2 and 6 are in the order of a few
> >seconds. And it's the only time the users will not have access to the MV,
> >as
> >opposed to a full refresh using dbms_mview.refresh approach., which will
> >lock the MV for the entire duration and generate tons of redo and
rollback.
> >
> >Even if you do a incremental refresh, this is still a better approach. In
> >that case, you don't drop the table during the refresh.
> >
> >(2) Yes, the option is available in 8i, at least in 8.1.7. Make sure the
> >syntax is correct.
> >
> >create materialized view MV1
> >on prebuilt table
> >refresh fast
> >as
> >select ... from ....
> >
> >In the article I mentioned, you can find the complete syntax.
> >www.proligence.com/downloads.html is the site. It also dscribes a step by
> >step solution to the issue and compares the common solution with this new
> >one.
> >
> >Hope this helps.
> >
> >Arup Nanda
> >
> >----- Original Message -----
> >To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
> >Sent: Friday, October 24, 2003 12:34 PM
> >refresh - for
> >
> >
> > > Hi Arup,
> > >
> > > This is a very good method. I would like to use it to modify some of
my
> > > data loading procedures. Here are my questions:
> > > 1. Do I need to create the table on the step 1 every time when I
refresh
> >the
> > > data If I refresh data once per day?
> > > 2. Is "ON PREBUILT TABLE" available on Oracle 8i? When I was trying
the
> > > method on Oracle 8i, I got missing keyword error on "PREBUILT".
> > >
> > > Dave
> > >
> > > >
> > > >Siddharth,
> > > >
> > > >I will offer a slightly out-of-the-box solution. Please read it
through
> > > >till the end to determine its applicability in your case.
> > > >
> > > >It seems yours refresh interval is once a day and you don't mind
stale
> > > >data for a max of 24 hours. You also refresh is complete, not
> > > >incremental. So, I would suggest the follwoing approach.
> > > >
> > > >(1) Create a table first
> > > >CREATE TABLE CT_PRODUCTID_VW
> > > >TABLESPACE ....
> > > >NOLOGGING
> > > >AS
> > > >SELECT .....
> > > >
> > > >(2) When you are ready to "refresh", drop the MV
> > > >DROP MATERIALIZED VIEW CT_PRODUCTID_VW;
> > > >
> > > >(3) Create the MV with the PREBUILT TABLE option.
> > > >CREATE
> > > >MATERIALIZED VIEW CT_PRODUCTID_VW
> > > >BUILD IMMEDIATE
> > > >REFRESH START WITH SYSDATE
> > > >NEXT (SYSDATE + 1)
> > > >ON PREBUILT TABLE
> > > >AS
> > > >SELECT
> > > > msi.segment1 productid,
> > > >...
> > > >
> > > >Your MV is not accessible between STEP 2 and STEP3, which is really a
> > > >dictionary update and takes about a second or so. So the "outage" is
> > > >really 1 second, not 1/2 hr.
> > > >
> > > >A few explanations are in order here.
> > > >
> > > >(1) Creating an MV on a Prebuilt Table does not consume more space.
The
> > > >segment that used to be a table simply becomes an MV.
> > > >(2) When you drop the MV, the MV is gone, but the table remains
> >instact.
> > > >(3) The table can be create by any means - export/import, SQL*Loader,
> > > >INSERT APPEND, etc.
> > > >(4) IT places less strain on the system comapred to the MV refresh
> > > >option, simply because the MV refresh truncates the segment and then
> > > >builds it.
> > > >
> > > >I presented a paper to the same effect at IOUG Live 2003. You can
> > > >download a modified version of the same from my website
> > > >www.proligence.com/downlaods.html, titled "Painless Master Table
Alter"
> > > >from the Presentations Section.
> > > >
> > > >HTH.
> > > >
> > > >Arup Nanda
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >----- Original Message -----
> > > >To: Multiple recipients of list ORACLE-L
> > > >Sent: Tuesday, October 21, 2003 3:59 AM
> > > >refresh
> > > >
> > > >
> > > >Hi Gurus,
> > > >
> > > >I have a materialized view, which is based on Oracle Apps tables and
on
> > > >remote database. The view refresh takes around ½ hour, during this
time
> > > >period I cannot see any records in the materialized view and
therefore
> > > >my application faces errors.
> > > >The following is the view definition
> > > >
> > > >CREATE
> > > >MATERIALIZED VIEW CT_PRODUCTID_VW
> > > >BUILD IMMEDIATE
> > > >REFRESH START WITH SYSDATE
> > > >NEXT (SYSDATE + 1)
> > > >AS
> > > >SELECT
> > > > msi.segment1 productid,
> > > > msi.description description,
> > > > msi.inventory_item_id inventory_item_id,
> > > > mc.segment1 product_family,
> > > > mc.segment2 product_type
> > > >FROM MTL_CATEGORY_SETS_at_CME_ODSPROD mcs,
> > > > MTL_CATEGORIES_at_CME_ODSPROD mc,
> > > > MTL_ITEM_CATEGORIES_at_CME_ODSPROD mic,
> > > > MTL_SYSTEM_ITEMS_at_CME_ODSPROD msi
> > > >where 1=1
> > > >and mc.structure_id = 50112
> > > >and mc.segment3 != 'SPARE'
> > > >and mc.global_name = 'US'
> > > >and mc.enabled_flag = 'Y'
> > > >and mcs.global_name = mc.global_name
> > > >and mcs.category_set_name = 'PROD GROUP'
> > > >and mic.category_set_id = mcs.category_set_id
> > > >and mic.category_id = mc.category_id
> > > >and mic.global_name = mc.global_name
> > > >and mic.organization_id = 1
> > > >and mic.inventory_item_id = msi.inventory_item_id
> > > >and msi.organization_id = mic.organization_id
> > > >and msi.global_name = mc.global_name
> > > >AND msi.auto_created_config_flag = 'N'
> > > >AND msi.item_type IN ('ATO MODEL','CONFIG SPARE','CONFIG
> > > >SUB','FEATURE PACK','PRODUCT LIST>$0','PTO MODEL','SPARE')
> > > >and msi.inventory_item_status_code IN
> > > >('ENABLE-MAJ','ENABLE-NON','ENABLE-OPT','NONORD')
> > > >
> > > >Please note that the tables referenced are remote tables and Oracle
> >Apps
> > > >tables and not logging on it is possible.
> > > >Please suggest an appropriate refresh mechanism to see the records
even
> > > >during refresh period.
> > > >
> > > >Thanks in advance.
> > > >
> > > >With Warm Regards
> > > >
> > > >
> > > >
> > > >Siddharth Haldankar
> > > >Zensar Technologies Ltd.
> > > >Cisco Systems Inc.
> > > >(Offshore Development Center)
> > > ># : 091 020 4128394
> > > >shaldank_at_cisco.com
> > > >s.haldankar_at_zensar.com
> > > >
> > >
> > > _________________________________________________________________
> > > Cheer a special someone with a fun Halloween eCard from American
> >Greetings!
> > > Go to

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> > >
> > > --
> > > Please see the official ORACLE-L FAQ: http://www.orafaq.net
> > > --
> > > Author: David Boyd
> > > INET: davidb158_at_hotmail.com
> > >
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> >--
> >Author: Arup Nanda
> > INET: orarup_at_hotmail.com
> >
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>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Arup Nanda
  INET: orarup_at_hotmail.com

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