Concepts Guide: 5/27 - Schema Objects

I found that reading the Guide is quite hard if you are already tired. ;-)

As always, I like pictures. Figure 5-1 on page 5-3 does justice. Although they would make their point more clear by labelling the schemas.

Was not aware of intra-block chaining (pp 5-5) - interesting concept. Especially since it does not affect performance (does not increase the number of IO calls).

Figure 5-3 is good in that it really helps to see the various pieces of a block and the row, including the headers.

As much as I hate how nulls are handled in Oracle, the one good thing is that I like how Oracle just does not even record information for null-trailing rows (ie, column-length not stored in block). Except, of course, if you have LONG data - DO NOT USE LONG! =)

I was not aware how table compression actually worked. Now that I know a little more about it, I am surprised the guide did not mention any limitations. For example, if a block has 100% unique data (uncompressable), would the symbol table still be built and populated? If not, what is the cut-off? At what point does Oracle deem compression worthwhile, pragamatically?

I have never seen a practical use for nested tables, but I'll keep my eyes open. I jumped to 27-7 as referenced just to see what it said. I still have never seen a practical use for nested tables.

The fact that sessions are "bound" to temp tables was new to me; I did not realize you could not do ddl on a temp table if is already bound to a session. Kinda makes sense, though. I wonder why they do not simply call it "locking"? =) Afterall, that is how normal tables are handled.

Ojbect Views really confuse me, not being familiar with the concept. And this being the Concepts Guide, I found that the short little blurb did not really help me much at all.

I also did not realize that one could put declaritive constraints on views; interesting way to propagate metadata information for restricted environments.

The short paragraph on Materialized View Logs did not do the concept any justice. I get the impression that either space and/or time was restrained when this section was done. =)

The intro section to Dimensions left my head whirling. I am not a Warehousing guy by any means; while I appreciate the extra background and the quasi-example, I find that it deep-dives too quick for me. And using an example of a year being tied to a year-row is just the most absurd thing I have ever heard. Why not a practical, real-life example that "anyone" can grasp?

Good discussion for sequences; I like how the good is balanced with the bad - the "Caution" is stronger than I expected, but I think very important and am glad to see that the authors made it stand out.

Nice long section on indexes. *grin* I always find it strange to find in 10g documentation references to "analyze table", when most of the time I believe they really mean collect stats, for which we are told to use dbms_stats instead. The intro to deterministic (user-defined) indexes was quite interesting. I would personally consider this an example of "black magic" in Oracle. Another one of those cases where there is a strong lack of practical examples.

Figure 5-7 starts out looking like a great pictoral example. However I found it to be quite confusing. Actually, what I really want to see is how an index is built, starting with one row. At the very least, it would be helpful to augment the figure with text explaining the function of the values for the branch blocks. However, excellent information on how searches are mathematically bounded (big-O notation).

Excellent piece on bitmap indexes; great examples, wonderful discourse. I appreciate the balanced approach to addressing the pros and cons of bitmap indexes, which may at the outset seem to be the pancea of query performance issues. The sidebar on cardinality was very well done as well.

The section on Index-organized tables was also quite interesting, however I wonder why, if they are so highly recommended for OLTP applications, why are they not more popular?

Application Domain indexes, and the Oracle Data Cartridge in general, are another area of black magic that I fear ever going back to. I dabbled in it once when attempting to define custom statistics for a function and never looked back. =) I am sure they have their place on some "True Expert"'s shelf, but not here....

Like IOTs, the Concepts Guide does a good job selling Clusters and Hash Clusters as beneficial methods, but I do not see many folks using it in Real Life. Is it merely the learning curve that keeps the standard DBA away from these features? We have a lot of third-party apps; shall we assume that the vendors simply do not have the expertise to utilize these fun but advanced toys?

Interesting stuff none-the-less.