Search

Top 60 Oracle Blogs

Recent comments

September 2013

Metrics vs Statistics



Here are  the tuning metrics tables (SQL  stats are not in “metric” tables per say)

(*DBA_HIST_…_HISTORY views are sort of confusing. AFAI remember they were storing alert history, but apparently they are used for adaptive thresholds – an area for future investigation)

MH900182646

Wait Metrics vs Wait Events



Here is a quick table comparison of  different types of metrics views

metric_tables

The first line of the table is the classic wait event and statistic views. The following lines are the metric views.  The metric views were introduced in Oracle 10g.

Why Metrics are good

Metric views compute deltas and rates  which hugely simplifying the ability to answer simple questions like “what is the I/O rate on my databases right now?” This question, before 10g, was surprisingly tedious to answer. To answer the question one would have to query v$sysstat  for example:

RAC in KVM is possible without iSCSI

(This post is for Jerry. He will know when he reads it)

I have been a great supporter of many flavours of virtualisation and my earliest experience with Xen goes back to Oracle VM 2 which was based on RHEL 4 and an early version of Xen. Why am I saying this? Because Xen is (was?) simple and elegant. Especially for building RAC systems: paravirtualised Linux was all you needed, and a dual-core machine: Xen is very lightweight even though recent achievements in processor architecture (nested page tables, single root IO virtualisation, others) make it more desirable to use hardware virtualisation with paravirtualised drivers. This is what this post is about!

Shared storage in Xen

As you know you need shared block devices for RAC for voting disks, OCR, data files, redo logs, the lot. In Xen that’s as straight forward as it gets:

Bitmap / Btree

Here’s a little note that came about after I tweeted an idle thought on Twitter yesterday

  • 12c allows you to have multiple indexes on the same columns on a table, although only one of them is allowed to be visible at any one time – you can do the same with any recent versions of Oracle “almost”, and without the invisibility requirements. (Thanks to Jason Bucata for suggesting the critical detail on this one.)
  • 12c allows you to have “partial” indexing on partitioned tables -  you can do the same with earlier versions of Oracle “almost” but only if the indexes are local indexes or globally partitioned.
  • 12c doesn’t officially allow you to create an index that is a bitmap in the past and a btree in the present (yet) – although you can almost do this in any recent versions of Oracle.

How to use (almost) the same column definition for two indexes on the same table:

Insync 13 Brisbane

Just a quick note to let you know I’ll upload the slides in the next few days

Endymion

Endymion is the third book in the Hyperion Cantos series by Dan Simmons.

After finding the last book a little patchy at times, this one returned to the same sort of pacing and thrust that made me love the first book. This story picks up nearly 300 years after the last one ends. The daughter of one of the characters from the previous book entered one of the time tombs and appeared in Hyperion 274 years later. Since then things have changed throughout the former web worlds and the church has a vested interest in keeping things the way they are. The last thing they need is a little girl, with the power to topple their stronghold on the galaxy, messing things up for them.

Oracle Cloud Control EMCLI : First Thoughts

Whilst waiting for a new version of Cloud Control, which will hopefully include my job scheduler enhancement requests, I decided to see if I could solve my problem using the command line interface (EMCLI). That spawned this very basic article.

I was initially really excited by the EMCLI, planning to pretty much replace my job creation with EMCLI scripts, but there seem to be a bunch of discrepancies with the EMCLI compared to the regular Cloud Control interface. Now I admit I’m a newbie at this, but here’s what I’ve seen so far.

10053 Trace Files - Global Stats on Partitioned Tables

One of the reasons why it's taken a while to get around to the next 10053 trace file post (apart from the more human reasons I talked about here) is that I'd planned to show how 10053 trace files can show whether the CBO has used Global Statistics on Partitioned Tables or not, which is the example that I used the first few times I gave the 10053 presentation.

Blogging

I think it was Andy C who first mentioned to me that one of the golden rules of blogging was never to apologise or justify your reasons for not blogging. I guess it's because so many people do it so often that it becomes tedious. But my blogging output has been so woeful in the past year or so that I thought it worth mentioning at least one reason why and what I might do to encourage myself to write more useful posts.

The Story of Two Boats and Why Justin Bieber Owes Me £120* (Part 2)

So why does Justin Bieber owe me £120?