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EnterpriseDB: Memory Management & Performance
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Memory management is tightly coupled with performance.  While performance can be impacted by design and internals such as locking mechanisms, without appropriate memory management, performance will suffer.

As with most items in the comparison between EnterpriseDB and Oracle, Oracle provides more functionality at the cost of complexity.  You can tweak many of the EnterpriseDB memory parameters if you have time to play with them.  In reality, you need only set a single parameter (edb_dynatune, Chapter 2) and EnterpriseDB will do the rest.

It is possible to install Oracle and accept default memory configurations.  I can honestly say that I have never seen a production instance that was configured that way.  Usually 8-10 configuration parameters must be tweaked for individual installations.

There used to be many more parameters that needed to be tweaked.  Recent versions of Oracle have simplified this step dramatically.  Configure several buffers and set some maximum and minimum memory limits and the database is ready to go.

Database memory structures are somewhat of an arcane science to most people but those memory structures are really very standard and are based on generally accepted theory and, at least conceptually, is not that different between database vendors.

Non-memory related performance is also fairly standardized.  The rule in a database to increase performance is to decrease locking and IO.  EnterpriseDB inherits one of the most advanced locking mechanisms, the multi-version concurrency control or MVCC. 

Oracle and EnterpriseDB use the same locking model (via different implementations) so that a reader does not wait for a writer and a writer does not wait for a reader.  Different database sessions may see a different version of the data depending on the operations being performed on that data.

Oracle users know about rollback segments and/or undo space.  MVCC is much the same in concept.  EnterpriseDB undo is "cleaned up" in a process called vacuuming while Oracle's undo is performed in another tablespace and is maintained in parallel.  The result is the same: highly efficient locking.

A benefit of MVCC is the ability to perform hot backups on your data.  Because each session will get its own version of the data should it need it (to maintain consistency), hot backups are feasible. 

Performance having to do with IO will be the same between EnterpriseDB and Oracle.  All database applications need to be analyzed and designed to make the best trade-offs between IO and overhead.  Decisions such as indexing and data relationships are the same for most any database.

Database professionals currently working with Oracle will have no problems understanding, configuring or troubleshooting memory and performance issues within EnterpriseDB.  The similarities between Oracle and EnterpriseDB are impressive.

Availability/Reliability

Oracle is the king of availability.  From RAC to Data Guard to Streams, Oracle currently holds the crown of availability.  EnterpriseDB does not provide the feature set of availability that Oracle does.

It does compete in the replication arena though.  With add-ons such as Slony I and II for EnterpriseDB to and from EnterpriseDB/PostgreSQL providing much of the same functionality as Streams Replication and Data Guard and the EnterpriseDB Replication Console providing data migration between Oracle and EnterpriseDB, EnterpriseDB is a highly available database.

The implementation of the availability is primarily via replication.  Replication, while fairly simple to configure, is different from Oracle replication.  Database professionals should not have a problem understanding, configuring or troubleshooting EnterpriseDB replication.  EnterpriseDB replication is covered in detail in Chapter 7.

The reliability of EnterpriseDB is truly enterprise-class.  PostgreSQL has been around for 20 years and has been considered a reliable production class database for 10.  Past performance is the best indicator of future performance.




This is an excerpt from the book "EnterpriseDB: The Definitive Reference" by Rampant TechPress.

  
 

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