In-memory Consistency

A comment on one of my early blogs about the 12c in-memory database option asked how Oracle would deal with read-consistency. I came up with a couple of comments outlining the sort of thing I would look for in a solution, and this note is an outline on how I started to tackle the question – with a couple of the subsequent observations. The data is (nearly) the same as the data I generated for my previous article on the (more...)

In-memory Aggregation

The title of this piece is the name given to a new feature in, and since I’ve recently blogged about a limitation of the in-memory option I thought I’d pick this feature as the next obvious thing to blog about. This is a bit of a non sequitur, though, as the feature seems to have nothing whatsoever to do with the in-memory option; instead it’s a cunning mechanism combining aspects of the star-transformation (but without the bitmap indexes), (more...)

Quiz night

Here’s a script to create a table, with index, and collect stats on it. Once I’ve collected stats I’ve checked the execution plan to discover that a hint has been ignored (for a well-known reason):

create table t2
        mod(rownum,200)         n1,
        mod(rownum,200)         n2,
        rpad(rownum,180)        v1
        rownum <= 3000

create index t2_i1 on t2(n1);

                method_opt => 'for all columns size 1'

explain plan for

LOB Length

It’s funny how you can make little savings in work all over the place in Oracle if you’re prepared to look a little closely at what’s going on. Here’s a quirky little example with LOBs and function calls that might just have some greater relevance in other situations. Here’s a little data set, and two queries that I might run against it:

create table tbl(
	c1      clob
lob (c1) store as c_lob(
	disable storage  (more...)

In-memory limitation

I’ve been struggling to find time to have any interaction with the Oracle community for the last couple of months – partly due to workload, partly due to family matters and (okay, I’ll admit it) I really did have a few days’ holiday this month. So making my comeback with a bang – here’s a quick comment about the 12cR2 in-memory feature, and how it didn’t quite live up to my expectation; but it’s also a comment (more...)

Viewing Figures

The day has just started in Singapore – though it’s just coming up to midnight back home – and the view counter has reached 4,00,009 despite the fact that I’ve not been able to contribute much to the community for the last couple of months. Despite the temporary dearth of writing it’s time to have a little review to see what’s been popular and how things have changed in the 10 months it took to accumulate the (more...)

Analogy – 2

I suggested a little while ago that thinking about the new in-memory columnar store as a variation on the principle of bitmap indexes was quite a good idea. I’ve had a couple of emails since then asking me to expand on the idea because “it’s wrong” – I will follow that one up as soon as I can, but in the meantime here’s another angle for connecting old technology with new technology:

It is a feature of in-memory column (more...)

Parallel Plans

I’ve popped this note to the top of the stack because I’ve added an index to Randolf Geist’s series on parallel execution skew, and included a reference his recent update to the XPLAN_ASH utility.

This is the directory for a short series I wrote discussing how to interpret parallel execution plans in newer versions of Oracle.


So is out with a number of interesting new features, of which the most noisily touted is the “in-memory columnar storage” feature. As ever the key to making best use of a feature is to have an intuitive grasp of what it gives you, and it’s often the case that a good analogy helps you reach that level of understanding; so here’s the first thought I had about the feature during one (more...)

Execution Plans

This is the index to a series of articles I’ve been writing for redgate, published on their AllThingsOracle site, about generating and reading execution plans. I’ve completed a few articles that haven’t yet been published, but I’ll add their URLs when they’re available.

I don’t really know how many parts it’s going to end up as – there’s an awful lot that that you could say about reading execution plans, even when you’re trying to cover just (more...)