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Exadata

How Exadata smartscans work

I guess everybody who is working with Oracle databases and has been involved with Oracle Exadata in any way knows about smartscans. It is the smartscan who makes the magic happen of full segment scans with sometimes enormously reduced scan times. The Oracle database does smartscans which something that is referred to as ‘offloading’. This is all general known information.

But how does that work? I assume more people are like me, and are anxious to understand how that exactly works. But the information on smartscans is extremely scarce. Of course there is the Oracle public material, which looks technical, but is little/nothing more than marketing. On My Oracle Support, I can’t find anything on the inner working. Even in the ‘Expert Oracle Exadata’ book (which I still regard as the best source of Exadata related information) there is no material on the mechanics of smartscans.

Enkitec + Accenture = Even More Awesomeness!

Enkitec is the best consulting firm for hands on implementation, running and troubleshooting your Oracle based systems, especially the engineered systems like Exadata. We have a truly awesome group of people here; many are the best in their field (just look at the list!!!).

This is why I am here.

This is also why Accenture approached us some time ago – and you may already have seen today’s announcement that Enkitec got bought!

Mysterious new Oracle compression type

As part of our research for our joint presentation at OGH.nl and E4 my colleague Frits Hoogland made an interesting discovery. He verified the compression format for updated rows previously compressed using Hybrid Columnar Compression (HCC). In that particular example we researched HCC data on Exadata storage. As you may know, reading HCC data in its compressed form is limited to Exadata, Pillar Axiom, and the ZFS Storage Appliance (ZFSSA).

Background

Mysterious new Oracle compression type

As part of our research for our joint presentation at OGH.nl and E4 my colleague Frits Hoogland made an interesting discovery. He verified the compression format for updated rows previously compressed using Hybrid Columnar Compression (HCC). In that particular example we researched HCC data on Exadata storage. As you may know, reading HCC data in its compressed form is limited to Exadata, Pillar Axiom, and the ZFS Storage Appliance (ZFSSA).

Background

Compression Units – 6

I received an email recently asking me if I knew how Oracle found specific rows and columns in a compression unit. This is a topic that I’ve spoken about a couple of times, and I’ve published several notes on the blog about it, including an image of a critical slide from one of my presentations, and I was expecting to find some notes somewhere about Oracle catalogues all the bits and pieces.

“external table write” wait events… but I am only running a query?

I was helping a customer debug some external table load problems.  They are developing some code to do massive inserts via external tables.  As the code was being tested, we saw a fair number of tests that were doing simple queries of an external table.  I expected to see “external table read” wait events, but was surprised when we saw more “external table write” wait events than reads.

I thought this was due to writes to the “log” file and possible “bad” file, but I had to be sure.  I searched the docs but could not find reference to this wait event.  I specifically was seeing the following:

How important is a Disaster Recovery site for you?

I regularly read threads on the oracle-l mailing list, and occasionally feel very tempted to reply to one. Just recently I saw one that I liked a lot. It is specifically about using an Oracle Database Appliance (ODA) as a Disaster Recovery (DR) solution for an Exadata system. The Exadata configuration was not specified, I assume it was a smaller (eighth rack/quarter rack) configuration.

There were lots of arguments pro and against that Exadata->ODA architecture, and that leads to a broader question: how important is DR for your organisation? This blog post is about my personal experience, and probably strongly influenced by where I live in work (Europe), yours might be different.

About the original discussion

How important is a Disaster Recovery site for you?

I regularly read threads on the oracle-l mailing list, and occasionally feel very tempted to reply to one. Just recently I saw one that I liked a lot. It is specifically about using an Oracle Database Appliance (ODA) as a Disaster Recovery (DR) solution for an Exadata system. The Exadata configuration was not specified, I assume it was a smaller (eighth rack/quarter rack) configuration.

There were lots of arguments pro and against that Exadata->ODA architecture, and that leads to a broader question: how important is DR for your organisation? This blog post is about my personal experience, and probably strongly influenced by where I live in work (Europe), yours might be different.

About the original discussion

Where does the Exadata storage() predicate come from?

On Exadata (or when setting cell_offload_plan_display = always on non-Exadata) you may see the storage() predicate in addition to the usual access() and filter() predicates in an execution plan:

SQL> SELECT * FROM dual WHERE dummy = 'X';

D
-
X

Check the plan:

12c pq_replicate

Another day, another airport lounge – another quick note: one of the changes that appeared in 12c was a tweak to the “broadcast” distribution option of parallel queries. I mentioned this in a footnote to a longer article a couple of months ago; this note simply expands on that brief comment with an example. We’ll start with a simple two-table hash join – which I’ll first construct and demonstrate in 11.2.0.4: