Search

OakieTags

Who's online

There are currently 1 user and 51 guests online.

Online users

Recent comments

Affiliations

Oracle

Top Misconceptions about DBaaS Snapclone

The last couple weeks I’ve been lucky enough to get time with a new ZFSSA Simulator, (it will be out soon for everyone, so you’ll have to just play with the current one available, patience grasshopper!

“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:

NL History

Even the simplest things change – here’s a brief history of nested loop joins, starting from 8i, based on the following query (with some hints):

select
	t2.n1, t1.n2
from
	t2,t1
where
	t2.n2 = 45
and	t2.n1 = t1.n1
;

There’s an index to support the join from t2 to t1, and I’ve forced an (unsuitable) index scan for the predicate on t2.

Basic plan for 8i (8.1.7.4)

As reported by $ORACLE_HOME/rdbms/admin/utlxpls.sql.
Note the absence of a Predicate Information section.

RHEL7 and Oracle Linux 7 beta

Nearly two weeks ago, Oracle announced the Oracle Linux 7 Beta 1. Being the Linux fanboy I am, I downloaded it straight away from here.

Oracle Linux is a clone of the Red Hat Enterprise Linux (RHEL) distribution. The RHEL7 beta, and therefore OL7 beta, distro is based on a cut of Fedora 19, although depending on who you ask, it’s possibly more a mix of Fedora 18, 19 and 20… Suffice to say, there are a lot of changes compared to the RHEL6/OL6 distribution.

Restoring Controlfile When AUTOBACKUP Fail

Allow me to present the snapshot of a day from the life of John--the DBA at Acme Bank. On this particular day a database John manages crashed entirely and had to be restored from the backup. He takes regular (backupset) RMAN backups to tape. Since everything--including the controlfile--had crashed, John had to first restore the controlfile and then restore the database. The controlfile is always backed up with the backup database command. John was sure of that. However, restore controlfile from autobackup gave the error:

RMAN-06172: no AUTOBACKUP found or specified handle is not a valid copy or piece

Without the controlfile, the recovery was stuck, even though all the valid pieces were there. It was a rather alarming situation. Others would have panicked; but not John. As always, he managed to resolve the situation by completing recovery. Interested to learn how? Read on.

Some new Oracle Database 12c Articles

I’ve recently put some new Oracle 12c articles on the website.

The privilege usage stuff is really cool. Normally, trying to figure out what you can remove from a user is always a complete pain in the ass. Some of the databases I’m currently working with have used GRANT like it’s going out of fashion. Trying to identify what is really necessary is a tough job. Features like this are going to be hard to wait for…

Cheers

Tim…

 

ASH Analytics- Tracking Down an Issue, Part I

This is the first of many posts I’ll do where we take a particular issue and trouble-shoot.  I’ll go through multiple scenarios to show the common steps to take via the Enterprise Manager 12c from discovery to identification to research to explanation.

This blog will use the following features:

Running scripts in CDBs and PDBs in Oracle Database 12c

You’ve been sold on the whole concept of the multitenant option in Oracle 12c and you are launching full steam ahead. Your first database gets upgraded and converted to a PDB, so you start testing your shell scripts and bang! Broken! Your company uses CRON and shell scripting all over the place and the multitenant architecture has just gone and broken the lot in one fell swoop! I think this will end up being a big shock to many people.

Coincindences

I had another of those odd timing events today that make me think that Larry Ellison has access to a time machine. I found (yet another example of a) bug that had been reported on MoS just a few days before it appeared on an instance I was running. How is it possible that someone keeps doing things that I’m doing, but just a few days before I do them !

For no good reason I happened to browse through a load of background trace files on an 11.2.0.4 instance and found the following in an “m000″ file:

REPVFY Diagnostics, Part I of…Well, A Zillion

There are a number of Verification Utilities for Enterprise Manager 12c, (EM12c) and I’ve written about them before, but today I’m going to start on the Repository Verification Utility, (REPVFY).  This will be an ongoing series, as there are so many valuable features rolled into the utility and new ones that will be added as new patc