Tanel Poder Blog

Back in the (really) old days, systemstate dumps had to be used for diagnosing hangs and finding blockers of hung databases.

When you troubleshoot an Oracle (performance) problem you usually want to find out what are the problem sessions doing (wrong) and then why are they doing it.

There was a question in Oracle-L about where is the LOB data actually stored (in the row or the LOB segments) and what are the exact conditions when a switch from one to another may happen.

There was a question in the twitter-sphere about whether using sequences (sequence.NEXTVAL) in your select query’s projection list would somehow disable smart scans happening?

I just noticed that (finally) in 11.2 this syntax is supported: SQL> CREATE DATABASE LINK demo_x2  2 CONNECT TO tanel IDENTIFIED BY password  3 USING 'exadb03:1521/DEMO'; Database link created.

In case you didn’t know, Jonathan Lewis’es new Oracle Core: Essential Internals for DBAs and Developers book is out (for a few weeks already).

If you work with SQL Trace files (and profile them) then you should check out the awesome novel use of the “external table preprocessor” feature explained by Adrian Billington here: http://www.oracle-developer.net/display.php?

Relax, I’m talking about the Oracle Database kernel here, not the corporation ;-) Here’s a couple of more reasons why not to play around with undocumented debug events unless you’re really sure why and how would they help to solve your specific problem (a…

Ok, I think it’s time to write another blog entry.

So, what he hell is that V8 Bundled Exec call which shows up in various Oracle 11g monitoring reports?!

I have uploaded the latest hacking session video.

In almost all of the Exadata migration projects I’ve been part of, the client sees immediate speedup & performance increase when testing their workload on Exadata (of course, we’ve made sure that we do plan & execute the tasks right).

There was a very good question asked in Oracle-L list today, which has bothered me too in past.

One of my blog readers recently dropped me an email noting that he had noticed some cache buffers chains latch contention recently and successfully troubleshooted it with LatchProf.

I just noticed that Jonathan Lewis has announced that he’s writing a new Oracle (fundamental) internals book, due to be out in November.

In May I received the IOUG Select Journal Editor’s Choice Award for my Systematic Oracle Latch Contention Troubleshooting article where I introduced my LatchProfX tool for advanced drilldown into complex latch contention problems (thanks IOUG and John Kan…

Today I received a question which was a good example of systematic problem solving approach.

I just wasted a few minutes troubleshooting one of my scripts – and realized that while SELECT … INTO :bind_variable does not error out when executed as top-level SQL, it doesn’t seem to populate the resulting bind variable: SQL> VAR blah VARCHAR2(10) SQL>

Steve Bamber has written up a case study of library cache latch contention troubleshooting of an Apex application with LatchProf.

Update: Based on the original MOATS built by Adrian Billington and myself, other folks have built cool variations of MOATS (either based on our code or written completely new ones): MOATS (original) by Adrian Billington & Tanel: https://github.com/oracle-…

A lot of people have asked me whether there’s some sort of index or “table of contents” of my TPT scripts (there’s over 1000 in my TPT script repo right now).

A few days ago I looked into a SQL Tracefile of some LOB access code and saw a LOBREAD entry there.

Wow, I wasn’t aware that Oracle can also do an implicit datatype conversion for literal strings during parsing phase!

Note that the live event is over by now, but you can see the recording from Enkitec.tv On Tuesday 22nd March I’ll hold two (yes two) Secret Oracle Hacking Sessions – about ORA-04031: unable to allocate x bytes of shared memory errors, cursor management is…

As I’m finishing up a performance chapter for the Exadata book (a lot of work!)

There was a question in LinkedIn forum about whether Linux Hugepages should be used in Oracle Exadata Database layer, as they aren’t enabled by default during ACS install.

I had a question about how to quickly identify which Oracle process runs out of which ORACLE_HOME on Linux.

I just noticed that there’s a new cursor_bind_capture_destination parameter in Oracle 11.2.0.2 (which is really more like Oracle 11gR3 version because of the large amount of new features in it, as opposed to just bugfixes).

Here are my UKOUG 2010 slides about Exadata migration performance, this is real life stuff, not repeating the marketing material: Tanel Poder – Performance stories from Exadata Migrations View more presentations from tanelp.

I’m talking about this: select-1from from dual; Looks like invalid, right?

As I promised last year, I have 2 christmas gifts for you.

A lot of people have started seeing “asynch descriptor resize” wait event in Oracle 11gR2.

If you’ve taken any shared pool dumps from 11g+ databases lately, you might have wondered about what all the memory allocation reason codes like SQLA^ea880c38, KGLS^da11791e might mean.

I was running tests on some very large tables on an Exadata cluster and found an interesting bug.

The title pretty much says it.

Basically the most fundamental (or biggest or most important) difference between nested loop and hash joins is that: Hash joins can not look up rows from the inner (probed) row source based on values retrieved from the outer (driving) row source, nested l…

Thanks to everybody who attended my OCW hacking session!

So, which number takes more bytes inside an Oracle row?

I finally finished my first Exadata performance troubleshooting article.

You probably already know that it’s possible to drop tables in Oracle read only tablespaces… (You did know that already, right?

I haven’t written any blog entries for a while, so here’s a very sweet treat for low-level Oracle troubleshooters and internals geeks out there :) Over a year ago I wrote that Oracle 11g has a completely new low-level kernel diagnostics & tracing infrastr…

Randolf Geist has written a good article about systematic troubleshooting of a PL/SQL memory allocation & CPU utilization problem – and he has used some of my tools too!

At Hotsos Symposium Training Day I used rlwrap with sqlplus – which gives nice command line editing and history capabilities for tools like sqlplus.

Here’s a little trick question.

Did you know that it’s possible to use EXPLAIN PLAN FOR CREATE INDEX ON table(col1,col2,col3) syntax for explaining what exactly would be done when an index is created?

I recently consulted one big telecom and helped to solve their sporadic performance problem which had troubled them for some months.

Some time ago I wrote that since Oracle 10.2, some of the buffer cache can physically reside within shared pool granules.

Gwen Shapira has written an article about a good example of a non-trivial performance problem.

Some time ago I wrote an article about the 10g+ SQL_ID being just a hash value of the SQL statement text.

I wrote a latch contention troubleshooting article for IOUG Select journal last year (it was published earlier this year).