Troubleshooting

Jonathan Lewis's picture

Fixed Stats

There are quite a lot of systems around the world that aren’t using the AWR (automatic workload repository) and ASH (active session history) tools to help them with trouble shooting because of the licensing requirement – so I’m still finding plenty of sites that are using Statspack and I recently came across a little oddity at one of these sites that I hadn’t noticed before: one of the Statspack snapshot statements was appearing fairly regularly in the Statspack report under the “SQL Ordered by Elapsed Time” section – even when the application had been rather busy and had generated lots of other work that was being reported. It was the following statement – the collection of file-level statistics:

Jonathan Lewis's picture

My session workload

My old website (www.jlcomp.demon.co.uk) will be disappearing in a couple of weeks – but there are a couple of timeless articles on it that are worth saving and although the popularity of this one has probably been surpassed by Tanel Poder’s Snapper script, or other offerings by Tom Kyte or Adrian Billington, it’s still one of those useful little things to have around – it’s a package to takes a snapshot of your session stats.

The package depends on a view created in the SYS schema, and the package itself has to be installed in the SYS schema – which is why other strategies for collecting the information have become more popular; but if you want to have it handy, here are the two scripts:

Jonathan Lewis's picture

Kill CPU

My old website (www.jlcomp.demon.co.uk) will be disappearing in a couple of weeks – but there are a couple of timeless articles on it that are worth saving and a method for soaking up all the CPU on your system with a simple SQL statement against a small data set is, surely, one of them. Here, then is a little script that I wrote (or, at least, formalised) 15 years ago to stress out a CPU:

Jonathan Lewis's picture

Stats collection time

Yesterday I posted a note about querying dba_optstat_operations to get a quick report of how long calls to dbms_stats had been taking but said I had another script that helped to fill some of the gaps it left. One of my readers points out fairly promptely that 12c enhances the feature considerably, with a view dba_optstat_operation_tasks that (for example) lists all the tables processed during a single call to gather_schema_stats.

Well, I wrote my script years (if not decades) before 12c came out, so I’m going to publish it anyway.

Jonathan Lewis's picture

Stats time

I don’t really remember how long it’s been since Oracle created an automatic log of how long a call to the dbms_stats package took, though it was probably some time in the 10g time-line. It wasn’t until it had been around for several years, though before I wrote little script (possibly prompted by a comment from Martin Widlake) that I’ve used occasionally since to see what’s been going on in the past, how variable stats collection times have been, and what unexpected dbms_stats call an application may have been making. Here’s what it currently looks like:

Jonathan Lewis's picture

Securefile space

Here’s a little script I hacked together a couple of years ago from a clone of a script I’d been using for checking space usage in the older types of segments. Oracle Corp. eventually put together a routine to peer inside securefile LOBs:

Jonathan Lewis's picture

Space Usage

Here’s a simple script that I’ve used for many years to check space usage inside segments.  The comment about freelist groups may be out of date  – I’ve not had to worry about that for a very long time. There is a separate script for securefile lobs.

Uwe Hesse's picture

How to fix a problem with the spfile in #Oracle

An invalid entry in the spfile may prevent the instance from starting up:

SQL> alter system set sga_target=500m scope=spfile;

System altered.

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORA-00821: Specified value of sga_target 512M is too small, needs to be at least 1392M

The instance doesn’t come up! This is easy to fix without having to restore the spfile from backup:

SQL> create pfile='/home/oracle/init.ora' from spfile;

File created.

SQL> host vi /home/oracle/init.ora

Now correct the value in the text file. I just removed the sga_target parameter from it here. Then

Jonathan Lewis's picture

DML and Bloom

One of the comments on my recent posting about “Why use pl/sql bulk strategies over simple SQL” pointed out that it’s not just distributed queries that can change plans dramatically when you change from a simple select to “insert into … select …”; there’s a similar problem with queries that use Bloom filters – the filter disappears when you change from the query to the DML.

This seemed a little bizarre, so I did a quick search on MoS (using the terms “insert select Bloom Filter”) to check for known bugs and then tried to run up a quick demo. Here’s a summary of the related bugs that I found through my first simple search:

jeremy.schneider's picture

Understanding CPU on AIX Power SMT Systems

This month I worked with a chicagoland company to improve performance for eBusiness Suite on AIX. I’ve worked with databases running on AIX a number of times over the years now. Nevertheless, I got thrown for a loop this week.

TLDR: In the end, it came down to a fundamental change in resource accounting that IBM introduced with the POWER7 processor in 2010. The bottom line is twofold:

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