partitioning

There an interesting example of a deadlock on the OTN database forum:

DEADLOCK DETECTED ( ORA-00060 )
[Transaction Deadlock]

Deadlock graph:
                       ---------Blocker(s)--------  ---------Waiter(s)---------
Resource Name          process session holds waits  process session holds waits
PS-00000001-00000011        92     423     S             33     128     S     X
BF-2ed08c01-00000000        33     128     S             92     423     S     X

One of the responses to the post points out that Oracle error ORA-00060 is an application error and the OP needs to fix his code – and that’s usually a valid comment, especially if the deadlock involves only TX enqueues, TM enquees or a mixture of both; but this deadlock is between a BF and a PS enqueue.

I posted this question on twitter earlier on today (It was a thought that crossed my mind during a (terrible) presentation on partitioning that I had to sit through a few weeks ago – it’s always possible to be prompted to think of some interesting questions no matter how bad the presentation is, though):

Quiz: if you create a virtual column as trunc(date_col,’W') and partition on it – will a query on date_col result in partition elimination?

The answer is yes – on the version of Oracle that I happened to have to hand (12c) the next time I had a few minutes spare. Here’s a quick and dirty demo – with data adjusted to the publication date, so you may need to adjust the code to your current date.

A quick check-list on testing new partitioning features:

• Step 1 – test with a small amount of data in place, just to see if it works at all
• Step 2 – test with a reasonably large amount of data in place so that you can spot any unexpected time being lost
• Step 3 – test with a few uncommitted transactions from other sessions so that you can spot locking problems easily
• Step 4 – test with SQL tracing enabled so that you can check the trace files for any recursive SQL threats
• Step 5 – (optional, and harder to recognise) test with event 10704 set so that you can check the trace files for locking threats

Whatever else you do, though, make sure that you always have some data in every object because Oracle has some special optimisations for dealing with partitions that are known to be empty so, in the absence of data, you may be testing something that will never happen in production.

I have a fairly strong preference for choosing simple solutions over complex solutions, and using Oracle-supplied packaged over writing custom code – provided the difference in cost THere’(whether that’s in human effort, run-time resources, or licence fees) is acceptable. Sometimes, though, the gap between simplicity and cost is so extreme that a hand-crafted solution is clearly the better choice. Here’s an idea prompted by a recent visit to a site that makes use of materialized views and also happens to be licensed for the partitioning option.

Thank you all who attended my sessions at NYOUG Fall Conference this morning. I appreciate spending you most precious commodity - your time - with me. I sincerely hope you found both the presentations enlightening as well as entertaining.

Please see the details of the sessions below along with the download links.

Keynote: Oracle 12c Gee Whiz Features

Yet another Oracle version is out and so are about 1500 new features in a variety of areas. Some are well marketed (e.g. pluggable database or the multitenant option) and some shine by their sheer usefulness. And there are some that do not get a whole lot of coverage but are are hidden gems. In this session you learned 12 broad areas of Oracle Database 12c I feel are worth learning about to make your job as a DBA or developer better, easier, smoother and, in some cases, even make it possible what was hitherto impossible or impractical.

As I discussed previously in Part I, the space occupied by orphaned row entries associated with asynchronously maintained global indexes is not automatically reclaimed by subsequent DML operations within the index. Hence the need to clean out these orphaned index entries via the various options discussed in Part II. However, a good question by Jason […]

In Part I, I discussed how global indexes can now be asynchronously maintained in Oracle 12c when a table partition is dropped or truncated. Basically, when a table partition is dropped/truncated with the UPDATE GLOBAL INDEXES clause, Oracle simply keeps track of the object numbers of those table partitions and ignores any corresponding rowids within the […]

I previously looked at how global index maintenance was performed when dropping a table partition prior to Oracle Database 12c. Let’s see how things have now changed since the introduction of 12c. Let’s start by creating the same partitioned table and global indexes as previously: If we look at the current state of affairs, all […]

Before I discuss another Oracle Database 12c new feature, Asynchronous Global Index Maintenance, thought it might be worthwhile discussing how Global Indexes were handled prior to 12c. I’ll begin by creating and populating a simple range partitioned table: I’ll now create two global indexes, one non-partitioned, the other partitioned: So we currently have two happy […]

In Partial Indexes Part I, we looked at how it was possible with the 12c database  to create a Partial Index based on data from only selected table partitions. The resultant Partial Index can be either a Global or Local Index. In Part I, we only really looked at Global Indexes, so let’s look at […]