Posts by Jeremiah Peschka

Managing Oracle Performance with Statistics

Oracle
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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…
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The Basics of Oracle Statistics

Oracle
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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…
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Oracle Flashback: Undeleting Data

Oracle
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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…
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Oracle Wait Events

Oracle
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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…
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Oracle HA & DR Basics [With Video]

Oracle
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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…
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Announcing sp_BlitzCache™ v2.4

SQL Server
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Welcome to sp_BlitzCache™ v2.4. This release brings a few changes and bug fixes. Fixed a logical error in detecting the output table. Thanks to Michael Bluett for pointing that out. Sorting by executions per second finally works. Thanks to Andrew Notarian and Calvin Jones for submitting this week. Added a @query_filter parameter – this allows…
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A Guide to Contributing Code

SQL Server
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So you’ve got a great idea for a new feature to add to sp_BlitzSomethingOrOther, what’s the best way to get started? The Documentation Says… If you read our code contribution guidelines, you should write new code, write a test, sign an agreement, and then send us your code. That’s technically correct, but it’s a daunting task. After…
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Sample output from the Oracle v$session_event table.

Introduction to the Oracle Data Dictionary

Oracle
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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…
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Five Oracle Myths

Oracle
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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…
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Getting Started with Oracle

Oracle
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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…
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Oracle Backup Basics for SQL Server DBAs [Video]

Oracle
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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…
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Monitoring Oracle with Statspack

Oracle
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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:…
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Generating Identities

SQL Server
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The only thing you ever need to use for database identity is an IDENTITY, right? Well, maybe. There are a lot of different options and they all have different pros and cons. IDENTITY columns The default way to identify objects in SQL Server is to use an INT or BIGINT column marked as an IDENTITY. This guarantees relatively sequential numbers, barring…
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Why Archive Data?

Oracle, SQL Server
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The data story so far Meet Margot. Margot is an application developer who works for a small company. Margot’s application collects and generates a lot of data from users including their interactions with the site, emails and texts that they send, and user submitted forms. Data is never deleted from the database, but only a…
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What’s New in Oracle 12.1.0.2?

Oracle
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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…
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Getting an Oracle Execution Plan

Oracle
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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 –…
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Backing Up an Oracle Database

Oracle
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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).…
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