Re: External table performance

I *think* I'd take the approach of treating this as a WH load job and run something like

INSERT INTO STAGING_TABLE SELECT * FROM EXTERNAL_TABLE; COMMIT; Staging table can and should be indexed as required.

Depending on the nature of the data in the external tables and the requirements around old data you might well have yet another real, partitioned data and post-load you would partition exchange into a new partition, but the base argument, like Kims, is get the data into the database where the normal power of the dbms engine can be appropriately used.

There are also enhancements to external tables in 12.2 that might be worth looking at.

On Sun, Jan 14, 2018 at 9:24 AM, Kim Berg Hansen <kibeha_at_gmail.com> wrote:

> Hello, Sanjay
>
> You write the external table is extensively used and indexes could be
> helpful. You've thought about MVs, and I would suggest you try that.
> The "problem" with the external table in your case seems that you often
> query just "some rows" (particularly a given state/county/period), but
> querying an external table has to read the entire file every time you query
> it.
>
>
> What I often do for such situations is something like this:
>
> - Create external table.
> - Create materialized view REFRESH COMPLETE ON DEMAND as select * from
> external table.
> - Create desired index(es) on state, county, period, whatever you need on
> the mview.
> - In the procedure or script or whatever updates a new file, include a
> call to DBMS_REFRESH.REFRESH to do a complete refresh of the mview right
> after the new file is in place.
> - Use the mview in all your queries. (In this case since you have existing
> queries, perhaps rename the external table to something else and give the
> mview the original name of the ext.table.)
>
>
> I've used this method often. For example we had a case of having to
> retrieve datafiles from a datasupplier regularly via FTP.
> I wrote a procedure that used FTP_UTIL_PKG (from Tim Hall, ORACLE-BASE) to
> retrieve the files and then call DBMS_REFRESH.REFRESH.
> This procedure was then called periodically by scheduler (or DBMS_JOB) and
> that way the mview was continually refreshed with the content of the files
> from the FTP server.
> And all our queries used the mview that had suitable indexes on it.
>
> Just a suggestion :-)
>
>
> Cheerio
> /Kim
>
>
> Regards
>
>
> Kim Berg Hansen
> Oracle ACE
>
> http://www.kibeha.dk
> kibeha_at_kibeha.dk
> _at_kibeha <http://twitter.com/kibeha>
>
>
>
> On Fri, Jan 12, 2018 at 9:29 PM, Sanjay Mishra <
> dmarc-noreply_at_freelists.org> wrote:
>
>> Mark
>>
>> Oracle 12.1.2 and it is Single Node RAC instance and is Enterprise
>> Edition. The issue with Select is where Clause for 2-3 column where Index
>> can definitely be helpful but External table dont allow index. Select was
>> Tried with Parallel but no difference in terms of performance. One option
>> trying is MV and as data is not much but table is extensively used for
>> various purpose.
>>
>> Sanjay
>>
>> On Friday, January 12, 2018, 2:29:48 PM EST, Powell, Mark <
>> mark.powell2_at_dxc.com> wrote:
>>
>>
>> Sanjay, you did not identify your Oracle version and edition nor post the
>> actual code you have an issue with but consider the following.
>>
>> I do not have access to a server where I can test right now but I believe
>> that you can select from an external table using parallel query if you are
>> on EE.
>>
>>
>> Mark Powell
>> Database Administration
>> (313) 592-5148
>>
>>
>> ------------------------------
>> *From:* oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> on
>> behalf of Sanjay Mishra <dmarc-noreply_at_freelists.org>
>> *Sent:* Friday, January 12, 2018 2:23:40 PM
>> *To:* Oracle-L Freelists
>> *Subject:* External table performance
>>
>> Can someone share the Tuning activites that can be done for Selecting
>> data from External table in 12c (12.1)? I am working on project that is
>> getting every 6hourly data as flat file from external source and then has
>> to be selected from ORacle table for some processing. Data is only 50K
>> records but Select is taking time. It is Local Storage where File is
>> located. I don;t think we can have indexes yet and so checking experience
>> from the experts.
>>
>> Tx
>> Sanjay
>>
>
>

-- 
Niall Litchfield
Oracle DBA
http://www.orawin.info

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