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Oracle

Quick Pluggable Database (PDB) Update…

I’ve been playing around with using SQL Developer and Cloud Control 12cR3 for managing pluggable databases (PDBs) this morning. I’ve added a couple of quick references to my PDB article.

If you understand the DBCA and SQL*Plus approach, the SQL Developer and Cloud Control screens are pretty self explanatory, so I’ve made my references to them brief. :)

Cheers

Tim…

TCP Trace Analysis for NFS

How do we know where latency comes from when  there is a disparity in reported I/O latency on  the I/O subsystem and that of the latency reported on the  client box requesting the I/O.

For example if I have an Oracle database requesting I/O  and Oracle says an 8Kb request takes 50 ms yet the I/O storage subsystem says 8Kb I/Os are taking 1ms (averages) , then where does the 49  extra ms come from?

When the I/O subsystem is connected to Oracle via NFS  then there are a lot of layers that could be causing the extra latency.

Screen Shot 2013-08-23 at 1.35.20 PM

Where does the difference in latency come from between NFS Server and Oracle’s timing of pread?

Oracle time units in V$ views

Oracle has a crazy mix of units of time in various v$ views

  • seconds
  • centi-seconds
  • milliseconds
  • microseconds

Some are straight forward such as time_waited_micro, but what unit is “TIME_WAITED”  or “WAIT_TIME” in? For example

v$session
WAIT_TIME -  centi
SECONDS_IN_WAIT – seconds

v$session_wait
WAIT_TIME – centi
SECONDS_IN_WAIT – seconds

v$system_event
TIME_WAITED – centi
AVERAGE_WAIT – centi
TIME_WAITED_MICRO – micro

v$system_wait_class
TIME_WAITED – centi

v$eventmetric
TIME_WAITED – centi

Oracle 12c Multitenant Option : CDBs and PDBs…

I started trying to play with the Oracle multitenant option (all that pluggable database stuff) a little while ago and gave up. It’s wasn’t that it was that difficult. More than anything my problem was I didn’t know what to focus on first. There is so much to it and it’s all interrelated, so you start to write about one small piece and before you know it your article has lost focus and is growing too big. As a result I decided to let it simmer in the background and start looking at some of the other smaller 12c new features first…

My next stumbling block was just about everything in 12c seems to relate back to pluggable databases in some way. So you either pretend it doesn’t exist and have gaping wholes in everything you write, or you have to bite the bullet and get to grips with pluggable databases. So back I came to pluggable databases…

Scalar Subqueries in Oracle SQL WHERE clauses (and a little bit of Exadata stuff too)

My previous post was about Oracle 12c SQL Scalar Subquery transformations. Actually I need to clarify its scope a bit: the previous post was about scalar subqueries inside a SELECT projection list only (meaning that for populating a field in the query resultset, a subquery gets executed once for each row returned back to the caller, instead of returning a “real” column value passed up from a child rowsource).

I did not cover an other use case in my previous post – it is possible to use scalar subqueries also in the WHERE clause, for filtering the resultset, so let’s see what happens in this case too!

Enkitec is a finalist for the UKOUG Engineered Systems Partner of the Year Award

Enkitec has made it to the shortlist of UKOUG Partner of the Year Awards, in the Engineered Systems category. So if you like what we have done in the Exadata and Engineered Systems space, please cast your vote! :-)

Note that you need to be an Oracle user – using your company email address in order to vote. (the rules are explained here).

Thanks!!!

C-MOS: How to get rid of the annoying “The Page has Expired” dialog in My Oracle Support

So, how many of you do hate the dialog below?

MOS page expired dialog

Good news – there is a fix! (or well, a hack around it ;)

Before showing the fix, you can vote & give your opinion here:

Distributed Queries – 3

A comment I’ve made many times in the past about distributed queries is that Oracle doesn’t try to retrieve histogram information from remote databases when optimizing a query. Checking back through previous posts, though, I don’t think I’ve ever mentioned it on the blog – so here’s an example demonstrating the point.

I’ll start with 11.2.0.3, with some fixed system stats (as they could make a difference to repeatability), and the following data set.

Please, please, please instrument your code!

I’m always telling people to instrument their code. Invariably they don’t. Then this happens:

MV Refresh

Here’s a funny little problem I came across some time ago when setting up some materialized views. I have two tables, orders and order_lines, and I’ve set up materialized view logs for them that allow a join materialized view (called orders_join) to be fast refreshable. Watch what happens if I refresh this view just before gathering stats on the order_lines table.

I have a little script that start with “set echo on”, then calls two packaged procedures, one to refresh the join view, the other to collect stats on the order_lines table; here’s the output from that script: