IOT

dbakevlar's picture

Oracle IOTs against SQL Server Clustered Indexes

I’m itching to dig more into the SQL Server 2016 optimizer enhancements, but I’m going to complete my comparison of indices between the two platforms before I get myself into further trouble with my favorite area of database technology.

dbakevlar's picture

Smart Home Update

I make some odd New Year’s Resolutions and mine for 2017 was to add some smart home solutions to our home that made sense.  I’ve seen what can happen if you don’t plan these types of projects out well, (looking at you, Mark Rittman!) and the insanity that ensues!

Jonathan Lewis's picture

IOT limitation

In the right circumstances Index Organized Tables (IOTs) give us tremendous benefits – provided you use them in the ideal fashion. Like so many features in Oracle, though, you often have to compromise between the benefit you really need and the cost of the side effect that a feature produces.

Jonathan Lewis's picture

RI Locks

RI = Referential Integrity: also known informally as parent/child integrity, and primary (or unique) key/foreign key checking.

I’m on a bit of a roll with things that I must have explained dozens or even hundreds of times in different environments without ever formally explaining them on my blog. Here’s a blog item I could have done with to response to  a question that came up on the OTN database forum over the weekend.

What happens in the following scenario:

Jonathan Lewis's picture

Auto Sample Size

In the past I have enthused mightily about the benefits of the approximate NDV mechanism and the benefit of using auto_sample_size to collect statistics in 11g; however, as so often happens with Oracle features, there’s a down-side or boundary condition, or edge case. I’ve already picked this up once as an addendum to an earlier blog note on virtual stats, which linked to an article on OTN describing how the time taken to collect stats on a table increased dramatically after the addition of an index – where the index had this definition:

Jonathan Lewis's picture

IOT Catalogue

I’ve just added a catalogue of Richard Foote’s articles on IOTs to the list I made a couple of years ago of Martin Widlake’s articles, so this is just a temporary note to point people to the updated list.

OIC(A) again

Issues with OICA/OIC (OPTIMIZER_INDEX_COST_ADJ/OPTIMIZER_INDEX_CACHING) parameters have already been mentioned many times. Recently I’ve noticed one more and I think I didn’t see this case somewhere else on the Internet so I’ll share it.


Here’s a simple table T1 holding 1M rows with the indexed column X having 10 distinct values:

Richard Foote's picture

IOT Secondary Indexes – The Logical ROWID Guess Component Part II (Move On)

Having mentioned a couple of dangers associated with IOT Secondary Indexes, thought I might discuss a couple of their nicer attributes. In the previous post, we saw how 50-50 index block splits on the ALBUM_SALES_IOT IOT table caused rows to move to new leaf blocks, resulting in a degradation in the PCT_DIRECT_ACCESS value of the associated ALBUM_SALES_IOT_TOTAL_SALES_I secondary [...]

Richard Foote's picture

IOT Secondary Indexes – The Logical ROWID Guess Component Part I (Lucky)

As discussed previously, an index entry within a Secondary Index on an Index Organized Table (IOT) basically consists of the indexed column(s) and the Logical Rowid, the PK column(s) and a “guess” to the physical block in the IOT containing the corresponding row. Let’s discuss this “guess” component in a bit more detail. When the Secondary [...]

Richard Foote's picture

IOT Secondary Indexes: Primary Key Considerations (Beauty And The Beast)

As discussed previously, one of the nice features of an IOT Secondary Index is that it contains the mandatory Primary Key of the IOT, which is always maintained and can be used to access the necessary rows of the IOT regardless of  row movement within the IOT itself. This can also be beneficial if only the PK [...]

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