Cache anomaly
Just a quick heads-up for anyone who likes to play around with the Keep and Recycle caches.In 11g Oracle introduced the option for serial direct path reads for tablescans on tables that was...
View ArticleCoincindences
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...
View ArticleBigfiles
It’s always the combinations that catch you out.Bigfile tablespaces have their uses – especially in big systemsMaterialized views have their users – especially in big systemsThere’s absolutely no...
View ArticleCosting Bug
It’s amazing how you can find little bugs (or anomalies) as soon as you start to look closely at how things work in Oracle. I started to write an article for All Things Oracle last night about...
View ArticleSubquery with OR
Prompted by a pingback on this post, followed in very short order by a related question (with a most gratifying result) on Oracle-L, I decided to write up a note about another little optimizer...
View ArticleIgnoring Hints
Does Oracle ignore hints – not if you use them correctly, and sometimes it doesn’t ignore them even when you use them incorrectly!Here’s an example that I’ve run on 11.2.0.4 and 12.1.0.1 create table...
View ArticleSecurefiles
A few weeks ago someone emailed me about a problem they had importing securefiles – it was very slow. Such things are never easy to address by email, of course, but there were three features to...
View ArticleSecurefiles
A few weeks ago someone emailed me about a problem they had importing securefiles – it was very slow. Such things are never easy to address by email, of course, but there were three features to...
View ArticleDelete Costs
One of the quirky little anomalies of the optimizer is that it’s not allowed to select rows from a table after doing an index fast full scan (index_ffs) even if it is obviously the most efficient (or,...
View ArticleDelete Costs
One of the quirky little anomalies of the optimizer is that it’s not allowed to select rows from a table after doing an index fast full scan (index_ffs) even if it is obviously the most efficient (or,...
View ArticleCache anomaly
Just a quick heads-up for anyone who likes to play around with the Keep and Recycle caches.In 11g Oracle introduced the option for serial direct path reads for tablescans on tables that was...
View ArticleCache anomaly
Just a quick heads-up for anyone who likes to play around with the Keep and Recycle caches.In 11g Oracle introduced the option for serial direct path reads for tablescans on tables that was...
View ArticleGroup By Bug
This just in from OTN Database Forum – a surprising little bug with “group by elimination” exclusive to 12c. alter session set nls_date_format='dd-Mon-yyyy hh24:mi:ss'; select /*...
View ArticlePlan depth
A recent posting on OTN reminded me that I haven’t been poking Oracle 12c very hard to see which defects in reporting execution plans have been fixed. The last time I wrote something about the problem...
View Articlefirst_rows(10)
No, not the 10th posting about first_rows() this week – whatever it may seem like – just an example that happens to use the “calculate costs for fetching the first 10 rows” optimizer strategy and does...
View Article12c Downgrade
No, not really – but sometimes the optimizer gets better and gives you worse performance as a side effect when you upgrade. Here’s an example where 11.2.0.4 recognised (with a few hints) the case for a...
View ArticleInvalidation
Someone who attended my sessions at the Bucharest Oracle Summit earlier on this year sent me an example of a quirky little bug, possibly related to the newer “fine-grained” invalidation mechanisms,...
View ArticleSubquery Factoring (10)
What prompted me to write my previous note about subquerying was an upgrade to 12c, and a check that a few critical queries would not do something nasty on the upgrade. As ever it’s always interesting...
View ArticleIN/EXISTS bugs
Here’s a simple data set – I’m only interested in three of the columns in the work that follows, but it’s a data set that I use for a number of different models:read more
View ArticleResult Cache
Yesterday I thought I’d spend half an hour before breakfast creating a little demonstration of a feature; some time about midnight I felt it was time to stop because I’d spent enough time chasing...
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