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January 2014

12c Online Partitioned Table Reorganisation Part II (Move On)

In Part I, we looked at some of the issues associated with locking and unusable indexes when Moving both tables and table partitions. The Oracle 12c Database has introduced a number of great new capabilities associated with online DDL activities. One of these really useful features is the capability to now move table partitions online while […]

Does parallel_degree_limit work with parallel_degree_policy=manual?

The Oracle 11g parameter parallel_degree_limit is designed to put a cap on the maximum DOP for a statement.

The Oracle Database Reference 11g Release 2 (11.2) says this:

A numeric value for this parameter specifies the maximum degree of parallelism the optimizer can choose for a SQL statement when automatic degree of parallelism is active. Automatic degree of parallelism is only enabled if PARALLEL_DEGREE_POLICY is set to AUTO or LIMITED.

But that’s not entirely correct because it turns out you can enable auto DOP via a hint. The PARALLEL hint without a valid object on which to act will enable auto DOP for the statement. Here is an example:

OEM CLI Commands for Bulk Property Changes

This will be a brief post, mostly so I can save this command somewhere besides the bash_history file on my OEM server. It may prove useful to a few others too… it has been absolutely essential for me on several occasions! (I was just using it again recently which reminded me to stick it in this blog post.) This is how you can make bulk property changes to a large group of targets in OEM:

OEM CLI Commands for Bulk Property Changes

This will be a brief post, mostly so I can save this command somewhere besides the bash_history file on my OEM server. It may prove useful to a few others too… it has been absolutely essential for me on several occasions! (I was just using it again recently which reminded me to stick it in this blog post.) This is how you can make bulk property changes to a large group of targets in OEM:

OEM CLI Commands for Bulk Property Changes

This will be a brief post, mostly so I can save this command somewhere besides the bash_history file on my OEM server. It may prove useful to a few others too… it has been absolutely essential for me on several occasions! (I was just using it again recently which reminded me to stick it in this blog post.) This is how you can make bulk property changes to a large group of targets in OEM:

Single block reads

When a “cache read” tablescan (or index fast full scan) takes place we generally expect to see waits on “db file scattered read” as Oracle performs multi-block reads to do the scan. But we all know that Oracle will skip over blocks that are already in the cache and can therefore end up doing multi-block reads of many different sizes, even down to the point where it does single block reads (waiting for “db file sequential read”).

A quirky little question came up on OTN a little while ago: “for a large table we expect multiblock reads to be positioned at the end of the LRU for prompt re-use; but when Oracle does a single block read as part of a tablescan does it go to the end of the LRU (because it’s part of a large tablescan) or does it go to the mid-point of the LRU (because it’s a single block read)?”

xDollar

I see Tanel has just started a short series of articles on where the X$ data come from so, for those with time on their hands (?anyone?) here’s a little script I wrote a few years ago when I wanted to check which v$ objects corresponded to the same internal structure in the SGA: (as v$session and v$session_wait used to)

It starts with a function that has to be created in the SYS schema – so no doing this on production systems. The it’s a pipelined function so that we can treat its output like a table, which means I need to create an object type and a table type before creating the function.  In the function I select each x$ name from the list of x$ names (x$kqfta) and for each table I construct a dynamic SQL statement selecting the first row from the table.

Public Speaking Tips

I figured this would be a series of 5 posts max and it ended up being two weeks of daily posts. :)

Here is the list of posts:

Public Speaking Tip 14 : What do I present? (the pursuit of cool)

Deciding what to speak about is one of the most difficult things to do. I still struggle with it now, but this last year has been a turning point for me. I’ve already said you should present about something you are interested in, but what?

It is very easy to fall into the trap of “the pursuit of cool”. You quite fancy doing a presentation on subject X, but think it’s not new or cool enough. The pursuit of cool also makes you question how your choice will be perceived by others, because you are trying to impress specific people or groups of people. If you feel yourself falling into the trap of the pursuit of cool, just remember the following:

Public Speaking Tip 13 : Understand your motivation for speaking

In yesterday’s post I talked about what I believe is the most important reason for public speaking, but different people have different motivation and I think it’s good for you to understand what you want to get out of the experience, as it might affect how you approach the journey.

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