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Oracle Performance Tuning – ASH Basics
Recently I got an opportunity to dig into performance of database. We were not facing any performance issue, but we wanted to understand whats happening under the hood. What are the bottlenecks and how...
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Apache Cassandra – NoSQL storage solution
These days I am exploring another storage solution – Cassandra. Apache Cassandra datastore was originally developed by Facebook as open source NoSQL data storage system. Its actually based on Amazon’s...
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Pointing MySQL Read-Replica to new master after failover
Here I am describing a simple scenario where we have a read replica (other than slave) which is currently pointing to master mysql instance. We have another slave which is also pointing to same master....
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direct path read behavior in Oracle 11.2
Prior to 11g, whenever optimizer goes for full table scan, Oracle used to show “db file scattered read” as wait event. But starting from 11g, a full table scan can show (depending on certain...
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Tracing Single SQL in Oracle
Many times, while doing SQL tuning, we want to trace (event 10046) single SQL in database. Instead of going for module level tracing or session level using DBMS_MONITOR, we can simply use below alter...
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Affect of object Statistics on SQL Execution statistics
This is a small article to demonstrate why correct statistics are important and how they affect execution statistics of same plan. In the past we learned that changing table statistics or index...
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Cassandra 2.0 Architecture
In this article, I will cover various key structures that makes up Cassandra. We will also see what structure resides in memory and what resides on disk. In next article, I will give an overview of...
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Coverting MySQL database character set to UTF8
Recently I was engaged to convert the character set for few MySQL databases from latin1 to UTF8 collation utf8_general_ci. This article describes the approach taken for doing the same. First I will...
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How many checkpoints in Oracle database ?
This Question came to my mind when I was discussing “direct path reads” with DBA candidates. I was surprised that many DBAs were not aware of object level checkpoint that happens while doing direct...
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Brief about Workload Management in Oracle RAC
This is a brief article about workload management in RAC. I tried to cover different components of workload management in RAC and how they are configured at client side or server side. I haven’t gone...
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Latches: What do we know ?
Latches are low level serialization mechanism which protects memory areas inside SGA. They are light wait and less sophesticated than enqueues and can be acquired and released very quickly. Latch...
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Mutex: What do we know ?
In my previous article on Latches, I mentioned various things related to latches including different types and their behavior. In this article I will describe similar things about mutexes. Mutex are...
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Library Cache: Mutex X – Bug 20879889 – Fixed in 11.2.0.4
I recently encountered a bug related to MView log causing very high library cache: mutex x wait events. I will brief about the debugging steps I tried and fix for the same. Few things to note before I...
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Previewing Backup Restore
Introduction: This is a short article on RMAN where we can check if our backups are really intact and can help us in critical situation when we have to restore and recover the database. We have a...
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Oracle 12c Learning Series: Automatic Data Optimization – ADO
I am starting Oracle 12c learning series, where I am planning to publish multiple articles on Oracle 12c new features. I hope these articles will be helpful to DBAs aspiring for OCP 12c certification...
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Using UDev to configure ASM disks
This is a small article on using UDev on RHEL 7. I have a virtual box with RHEL 7 and I am configuring ASM diskgroups. Before we configure ASM diskgroups, we need to have disks/partitions available at...
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Fixing SQL plans on ADG using SQL Profiles
With Active Dataguard setup, many of the read only applications runs on ADG and sometime the SQLs that are used by these applications runs into bad plans. ADG being a read only database, its not...
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Oracle 12c Learning Series: In-database Archiving and Temporal Validity
One of the major challenge faced by an Oracle DBA is – how to effectively deal with historical data? Today, if we consider database tables for an enterprise, data in the table goes back several years...
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Monitoring transaction recovery
Sometimes we end up in a situation where our long running transaction is not completing and we are also not sure how much further time it’s going to take. This happened with one of our DBA where they...
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Oracle 12c Learning Series: Automatic Table Recovery Using RMAN
Table recovery was possible in earlier release as well. Until previous release, if we wanted to recover a table, we had following options Database point in time recovery (DBPITR) Tablespace point in...
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