Oracle

Jonathan Lewis's picture

Closure

It’s been a long time since I said anything interesting about transitive closure in Oracle, the mechanism by which Oracle can infer that if a = b and b = c then a = c but only (in Oracle’s case) if one of a, b, or c is a literal constant rather than a column. So with that quick reminder in place, here’s an example of optimizer mechanics to worry you. It’s not actually a demonstration of transitive closure coming into play, but I wanted to remind you of the logic to set the scene.

kevinclosson's picture

Announcing SLOB 2.2 : Think Time and Limited-Scope User-Data Modification

This is a hasty blog post to get SLOB 2.2 out to those who are interested.

In addition to doing away with the cumbersome “seed” table and procedure.sql, this kit introduces 5 new slob.conf parameters. By default these parameters are disabled.

This SLOB distribution does not require re-executing setup.sh. One can simply adopt the kit and use it to test existing SLOB databases. The following explains the new slob.conf parameters:

DO_UPDATE_HOTSPOT=FALSE

When set to TRUE, modify SQL will no longer affect random rows spanning each session’s schema. Instead, each session will only modify HOTSPOT_PCT percent of their data.

HOTSPOT_PCT=10

This parameter controls how much of each session’s schema gets modified when UPDATE_PCT is non-zero. The default will limit the scope of each session’s data modifications to a maximum of 10% of their data.

dbakevlar's picture

OMS and OMR Performance- Part III, Metrics Page

Before heading off to UKOUG’s Tech 14 conference, thought I would jump back from the Agents performance page and look into the very important page in the Oracle Management Service, (OMS) and Oracle Management Repository, (OMR) regarding metrics.  Standard metrics collection is demanding in itself, so when we add plugins, metric extensions and manual metric collection changes, it’s important t

Jonathan Lewis's picture

Upgrades

I have a simple script that creates two identical tables , collects stats (with no histograms) on the pair of them, then executes a join. Here’s the SQL to create the first table:

fritshoogland's picture

Physical IO on Linux

I posted a fair amount of stuff on how Oracle is generating IOs, and especially large IOs, meaning more than one Oracle block, so > 8KB. This is typically what is happening when the Oracle database is executing a row source which does a full segment scan. Let’s start off with a quiz: what you think Oracle is the maximum IO size the Oracle engine is capable of requesting of the Operating System (so the IO size as can be seen at the SCI (system call interface) layer? If you made up your answer, remember it, and read on!

The real intention of this blogpost is to describe what is going on in the Oracle database kernel, but also what is being done in the Linux kernel. Being a performance specialised Oracle DBA means you have to understand what the operating system does. I often see that it’s of the utmost importance to understand how an IO ends up as a request at the NAS or SAN head, so you understand what a storage admin is talking about.

Jonathan Lewis's picture

Line Numbers

One of the presentations I went to at the DOAG conference earlier on this month was called “PL/SQL Tuning, finding the perf. bottleneck with hierarchical profiler” by Radu Parvu from Finland. If you do a lot of PL/SQL programming and haven’t noticed the dbms_hprof package yet make sure you take a good look at it.

A peripheral question that came up at the end of the session asked about problems with line numbers in pl/sql procedures; why, when you get a run-time error, does the reported line number sometimes look wrong, and how do you find the right line. I can answer (or give at least one reason for) the first part, but not the second part; Julian Dontcheff had an answer for the second bit, but unfortunately I failed to take a note of it.

dbakevlar's picture

Agents Management Via EM12c Release 4 Console

I’m going to take a break from the OMS/OMR Performance pages and jump over to the Agents page in release 12.1.0.4.  You can access this page from the Setup menu drop down in EMCC:

Jonathan Lewis's picture

Lunchtime quiz

There was a question on OTN a few days ago asking the following question:

Here’s a query that ran okay on 11g, but crashed with Oracle error “ORA-01843: not a valid month” after upgrade to 12c; why ?

The generically correct answer, of course, is that the OP had been lucky (or unlucky, depending on your point of view) on 11g – and I’ll explain that answer in another blog posting.

That isn’t the point of this posting, though. This posting is a test of observation and deduction. One of the respondants in the thread had conveniently supplied a little bit of SQL that I copied and fiddled about with to demonstrate a point regarding CPU costing, but as I did so I thought I’d show you the following and ask a simple question.’

pete.sharman's picture

The User Group Tour

Those of you that have been around Oracle for some time may already be aware of the various OTN tours. These tours bring well known speakers to some of the smaller (relatively speaking) regions that often don’t get to see some of the big name speakers, simply because of audience size. Over the past couple of years, I’ve been involved in the OTN APAC tour, and recently returned from the New Zealand leg of the tour for this year. I presented two workshops – one on Database Lifecycle Management and one on DBaaS – as well as standing in for a sick presenter and covering Snap Clone in Enterprise Manager 12c. For me, the best value for the conference was (as it so often is) the time spent interacting both with customers and other speakers / exhibitors. It was great to catch up with so many people I haven’t seen for a long time, both from within Oracle and outside of it.

Jonathan Lewis's picture

Baselines

I’m not very keen on bending the rules on production systems, I’d prefer to do things that look as if they could have happened in a completely legal fashion, but sometimes it’s necessary to abuse the system and here’s an example to demonstrate the point. I’ve got a simple SQL statement consisting of nothing more than an eight table join where the optimizer (on the various versions I’ve tested, including 12c) examines 5,040 join orders (even though _optimizer_max_permutations is set to the default of 2,000 – and that might come as a little surprise if you thought you knew what that parameter was supposed to do):

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