Oracle

pete.sharman's picture

EM Express versus EM Cloud Control

Recently I was asked the question “What is the real difference between EM Cloud Control [NOTE: I’ll refer to this as EM12c through the rest of this post] and EM Database Express in 12c?” It was (for me) a pretty easy question to answer, but I wanted to provide the questioner with a link to the place in the Enterprise Manager documentation where it covers that in detail. Somewhat to my surprise, I wasn’t able to find such a link – well, not quickly anyway. I think the reason for that is the documentation for EM Express (as it’s more commonly abbreviated to) falls under the database documentation which is owned by a different group in Oracle than the Enterprise Manager documentation. Well, that’s my speculation anyway. It may just be there in the documentation and I couldn’t find it in my quick search.

Jonathan Lewis's picture

Understanding SQL

From time to time someone publishes a query on the OTN database forum and asks how to make it go faster, and you look at it and think it’s a nice example to explain a couple of principles because it’s short, easy to understand, obvious what sort of things might be wrong, and easy to fix. Then, after you’ve made a couple of suggestions and explained a couple of ideas the provider simply fades into the distance and doesn’t tell you any more about the query, or whether they’ve taken advantage of your advice, or found some other way to address the problem.

Such a query, with its execution plan, appeared a couple of weeks ago:

pete.sharman's picture

Installing Enterprise Manager 12c For Testing

A question I get asked fairly often when I’m at conferences, either during the Q&A for my sessions or in general chit chat (a.k.a. networking) afterwards is “I want to play around with the features in Enterprise Manager 12c but don’t want to do that in our Production environment. How do I go about installing a copy of Enterprise Manager 12c somewhere else in the easiest way as a test environment?” The answer to that is pretty straightforward. It’s to download the relevant VM template from Oracle’s Software Delivery Cloud. Note: The screenshots shown in this post are from the new and enhanced Oracle Software Delivery Cloud, rather than the classic Software Delivery Cloud, so if you use the classic form your screens will be different. On the first screen, make sure you understand the export restrictions and click “Accept”:

dbakevlar's picture

SQL ID Specific Performance Information

When you need to have information about one SQL_ID and don’t need everything and the kitchen sink, there are a few different ways to collect this via Oracle.  I’m surprised how rarely this is covered in performance tuning/optimization, (whatever the current “acceptable” term is for fixing a database when there are performance issues arise… J)  classes, manuals and documentation.

Jonathan Lewis's picture

Migrated rows

I received an email recently describing a problem with a query which was running a full tablescan but: “almost all the waits are on ‘db file sequential read’ and the disk read is 10 times the table blocks”.  Some further information supplied was that the tablespace was using ASSM and 16KB block size; the table had 272 columns (ouch!) and the Oracle version was 11.2.0.4.

Jonathan Lewis's picture

Quiz Night

How many rows will you return from a single table query if you include the predicate


        rownum > 2

in the where clause.

Warning: this IS a catch question

To make it easier and avoid ambiguity, you may assume the table is the standard SCOTT.EMP table.

 

Part 2:

This posting was prompted by noticing a note that Dominic Brooks posted a few months ago.

Can you supply a workaround for the little oddity he’s described.

Jonathan Lewis's picture

Instance stats

+

pete.sharman's picture

Troubleshooting Target Status Availability Issues

If you’ve been using EM12c (or any of its precursors for that matter), you’d know that it can sometimes be problematic to troubleshoot an availability issue for targets.  You can see they might be up (hopefully!), down, pending, unreachable or showing a metric collection error, but understanding what’s causing that particular status (and indeed why it can sometimes be wrong) can be difficult at times.

Jonathan Lewis's picture

Parallel Query

According to the Oracle Database VLDB and Partitioning Guide (10g version and 11g version):

A SELECT statement can be executed in parallel only if the following conditions are satisfied:

Jonathan Lewis's picture

Efficiency

Here’s a question to which I don’t know the answer, and for which I don’t think anyone is likely to need the answer; but it might be an entertaining little puzzle for thr curious.

Assume you’re doing a full tablescan against a simple heap table of no more than 255 columns (and not using RAC, Exadata, In-memory, etc. etc. etc.), and the query is something like:


select  {columns 200 to 250}
from    t1
where   column_255 = {constant}
;

To test the predicate Oracle has to count its way along each row column by column to find column 255. Will it:

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