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
What I often do for such situations is something like this:
- Create external table.
- Create materialized view REFRESH COMPLETE ON DEMAND as select * from
- Create desired index(es) on state, county, period, whatever you need on
- 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 :-)
Kim Berg Hansen
On Fri, Jan 12, 2018 at 9:29 PM, Sanjay Mishra <dmarc-noreply@xxxxxxxxxxxxx>
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
On Friday, January 12, 2018, 2:29:48 PM EST, Powell, Mark <
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
*From:* oracle-l-bounce@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> on
behalf of Sanjay Mishra <dmarc-noreply@xxxxxxxxxxxxx>
*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