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partitioning

Interval Partition(s)

A quirky little feature of interval partitioning showed up on Twitter today – a parallel insert that would only use a single PX slave to do the inserting. With 1.1 billion rows and the option for running parallel 32 this made the loading process rather slower than it ought to have been.

Fortunately it’s quite easy to model (and work around) the oddity. So here’s a small data set and an empty partitioned table to work with:

Char problems

The semantics of comparing character columns of different types can lead to some confusion, so before I get into the main body of this note here’s a little test based on a table with one row:


create table t1(c2 char(2), c3 char(3), vc2 varchar2(2), vc3 varchar2(3));

insert into t1 values ('XX','XX','XX','XX');
commit;

select count(*) c2_c3   from t1 where c2 = c3;
select count(*) c2_vc3  from t1 where c2 = vc3;
select count(*) c3_vc2  from t1 where c3 = vc2;
select count(*) c3_vc3  from t1 where c3 = vc3;

I’ve inserted one row, using the same value for every single column; then I’ve been counting the row(s) where various pairs of columns match. Which (if any) of the four queries return the value 1 and which (if any) return the value zero ?

Online Statistics Collection during Bulk Loads on Partitioned Tables

Introduction

One of the enhancements to statistics collection and management in Oracle 12c was the ability of the database will automatically collect statistics during either a create-table-as-select operation or during the initial insert into a freshly created or freshly truncated table, provide that insert is done in direct-path mode (i.e. using the APPEND hint).
When that occurs, there is an additional operation in the execution plan; OPTIMIZER STATISTICS GATHERING.

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| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

Practical Application Performance Tuning: Applying Theory in Practice

I gave this presentation at the UKOUG Techfest 19 conference.  It is closely based on a previous presentation about PeopleSoft nVision performance tuning, and uses the experience of a PeopleSoft project as a case study, so I am also posting here and on my PeopleSoft blog.
This video was produced as a part of the preparation for this session.  The slide deck is also available on my website.

Split Partition

This is a little case study on “pre-emptive trouble-shooting”, based on a recent question on the ODC database forum asking about splitting a range-based partition into two at a value above the current highest value recorded in a max_value partition.

The general principle for splitting (range-based) partitions is that if the split point is above the current high value Oracle will recognise that it can simply rename the existing partition and create a new, empty partition, leaving all the indexes (including the global and globally partitioned indexes) in a valid state. There are, however, three little wrinkles to this particular request:

HIGH_VALUE (and other LONG columns) revisited

Just a quick post to ensure people don’t get caught out by a recent “trick” I saw on an AskTOM question for extracting the HIGH_VALUE out of it’s LONG storage in the dictionary to a more appropriate datatype. A reviewer (I’m sure in good faith) posted the following mechanism to extract the HIGH_VALUE

MERGE and ORA-8006

I’m sure there will be a slew of post-Kscope wrap up posts coming out into the blogosphere, so in lieu of that, and the the fact that I’m just stuck in an airport waiting for a flight, I’ll offer something slightly more technical. I did a post a while back about a curious error “unable to get a stable set of rows” when using MERGE. Here is another variant which can occur when you allow rows to physically move during a MERGE.

How is that possible?” I hear you ask. Easy. All we need is partitioned table with ENABLE ROW MOVEMENT.

MIN/MAX Optimization and Asynchronous Global Index Maintenance

In this short post I would like to point out a non-obvious issue that one of my customers recently hit. On the one hand, it’s a typical case where the query optimizer generates a different (suboptimal) execution plan even though nothing relevant (of course, at first sight only) was changed. On the other hand, in this case after some time the query optimizer automatically gets back to the original (optimal) execution plan.

Let’s have a look at the issue with the help of a test case…

The test case is based on a range partitioned table:

Re-partitioning 2

Last week I wrote a note about turning a range-partitioned table into a range/list composite partitioned table using features included in 12.2 of Oracle. But my example was really just an outline of the method and bypassed a number of the little extra problems you’re likely to see in a real-world system, so in this note I’m going to bring in an issue that you might run into – and which I’ve seen appearing a number of times: ORA-14097: column type or size mismatch in ALTER TABLE EXCHANGE PARTITION.

Re-partitioning – 18

In yesterday’s note on the options for converting a range-partioned table into a composite range/list parititioned table I mentioned that you could do this online with a single command in 18c, so here’s some demonstration code to demonstrate that claim: