Posts by Jeremiah Peschka

Oracle maintains statistics about data stored on disk. The statistics and histograms help guide the optimizer during query plan compilation. These statistics are usually helpful. Sometimes the statistics are not helpful. As data changes, the statistics collected by Oracle may become less accurate. If I’ve created a histogram on the column transaction_date, my histogram won’t…

Databases uses statistics about data to determine the best way to query tables. Should the database seek or scan? How many rows will be returned from tables that are being joined? Oracle is no exception, but the way Oracle treats statistics is different from SQL Server. Oracle Statistics Collection Just like SQL Server, Oracle can…

Or, “Oops, I didn’t mean to do that.” We’ve all had to deal with an accidental deletion or even a dropped table. Sometimes you leave off a where clause, sometimes you drop a table and find out that the change request listed the wrong table. Oracle uses a feature called Flashback to give database professionals…

Knowing what a query has been waiting on helps you figure out where you need to tune that system. Oracle’s wait interface provides a significant amount of information to help a DBA decide where to put tuning resources. There are multiple ways to see what Oracle has been waiting on: Right now: v$session_event For all time: v$system_event…

Oracle has different availability and recovery options from SQL Server. Being aware of what these options are and how you can use them will go a long way toward keeping your Oracle boxes just as safe as your SQL Server boxes. Here’s my 17-minute video explaining it, or you can keep reading and get your…

If you’re going to be working with Oracle, you need to be able to get a better handle on what’s going on with the Oracle database. Just like other database platforms, Oracle provides a data dictionary to help users interrogate the database system. Looking at System Objects Database administrators can view all of the objects…

It’s Hard to Configure Historically speaking, Oracle was a bit painful to configure. A DBA needed to be able to size internal components like the rollback segment, buffer cache, large object cache, sort area, and a number of other memory structures. This gave Oracle a reputation for being difficult to configure. Rightfully so – compared…

Let’s assume you want to get started with Oracle. Maybe your employer is switching to Oracle, maybe you just want a career change. Where do you go to get started? There’s no need to feel lost. Getting the Database You can get a hold of the Oracle database in two main ways – a VM…

To get ready for Tuesday’s webcast, here’s what you have to do: Watch the video below, but watch it today (or over the long weekend). There will be no live presentation this week and we won’t be rehashing all of the material in the video. Write down your questions or comments. (You don’t have to do…

At some point, you’re going to need to know what’s wrong with your Oracle instance. While there are a lot of monitoring tools around, there’s always some reason why third party monitoring tools can’t be installed. Oracle has shipped with something called Statspack that provides DBAs with some ability to monitor their Oracle instance. Statspack:…

Oracle 12.1.0.2 was recently released with some fanfare. One of the most talked about features is Oracle Database In-Memory, but there’s more to this release than just columnar storage. Big Investment in Data Warehousing Almost all of the new features reflect an increased focus on data warehousing. This is similar to recent SQL Server releases and, indeed, most…

Execution plans are fantastic – they make it easier to visualize how a query is running and find tuning opportunities. SQL Server DBAs starting with Oracle may be a bit frustrated by the lack of a clear way to get to execution plans. This covers three ways to get to execution plans in Oracle –…

One of a DBA’s most important tasks is taking backups of databases. As SQL Server DBAs, we’re used to using the same tools to backup the database that we use for the rest of our job. With Oracle, there are two main ways to back up a database: user managed backups and Oracle Recovery Manager (RMAN).…