When you configure a standby database, you want the application to transparently connect to the primary database, wherever it is. That’s the role of Transparent Application Failover, but this requires configuration on the client side. If you can’t configure TAF, you can use a virtual IP address. But then the question is how to configure the listener.ora to handle connections to this VIP.
Don’t worry, if you configured everything as recommended, with the hostname declared in /etc/hosts, and listener.ora referencing this host name, then you can simply ignore the VIP for your configuration. The reason is that when the host specified in the listener.ora resolves to the same IP address as the hostname of the server, then Oracle listener binds the port on all interfaces, and this includes the VIP.
When we have a tablespace with multiple datafiles, we are used to seeing the datafiles filled evenly, the extents being allocated in a round-robin fashion. In the old time, we used that to maximize performance, distributing the tables to all disks. Today, we use LVM striping, maximum Inter-Policy, ASM even distribution. And we may even use bigfile tablespaces, so that we don’t care about having multiple datafiles.
But recently, during test phase of migration, I came upon something like this:
It’s hard to understand all the ramifications of Oracle’s undo handling, and it’s not hard to find cases where the resulting effects are very confusing. In a recent post on the OTN database forum resulted in one response insisting that the OP was obviously updating a table with frequent commits from one session while querying it from another thereby generating a large number of undo reads in the querying session.
A recent OTN posting asked how the optimizer dealt with “like” predicates for character types quoting the DDL and a query that I had published some time ago in a presentation I had done with Kyle Hailey. I thought that I had already given a detailed answer somewhere on my blog (or even in the presentation) but found that I couldn’t track down the necessary working, so here’s a repeat of the question and a full explanation of the working.
The query is very simple, and the optimizer’s arithmetic takes an “obvious” strategy in the arithmetic. Here’s the sample query, with the equiavalent query that we can use to do the calculation:
I was in a COE, (Center of Excellence) meeting yesterday and someone asked me, “Kellyn, is your blog correct? Are you really speaking at a Blockchain event??” Yeah, I’m all over the technical map these days and you know what?
I’m itching to dig more into the SQL Server 2016 optimizer enhancements, but I’m going to complete my comparison of indices between the two platforms before I get myself into further trouble with my favorite area of database technology.
A recent posting on OTN raised the question of whether or not the “parallel” hint and the “first_rows(n)” hint were mutually incompatible. This reminded me that from time to time other posters on OTN (copying information from various websites, perhaps) have claimed that “parallel doesn’t work with first rows” or, conversely, “first rows doesn’t work with parallel”. This is one of those funny little myths that is so old that the script I’ve got to demonstrate the misconception is dated 2003 with a first test version of 220.127.116.11.
Since I haven’t run the test on any version of Oracle newer than 18.104.22.168 I thought it was time to dust it down, modernise it slightly, and run it again. So here’s the bit that creates a sample data set:
Here it is: plugin for Chrome. It took me 2 seconds to come up with a name – MOS-cow and about 3 hours to prepare plugin.
I just uploaded my slides from Collaborate 2017 to Slideshare, but also, the findings missing from my slide deck I used for Oak Table World on War of the Indices- Oracle and SQL Server. Feel free to download them here.