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Oracle 10gr2 and Oracle 11g sorting performance improvements

Oracle Tips by Burleson Consulting

Large Oracle disk sorting has traditionally been slower than third-party products, and super-large sort operations were sometimes executed by third-party sort products such as Syncsort and CoSORT's new FAst extraCT unload tool for Oracle (FACT).  This was especially true for data warehouse bulk loads operations (SQL*Loader), where huge datasets are pre-sorted before loading into the database.

As we know, sorting starts in Oracle PGA RAM (defined by the limits of sort_area_size and pga_aggregate_target 5% session limit), and a "disk sort" is invoked when the sort exceeds the maximum PGA allowed for the session.  Oracle says that the new sorting makes use of more PGA RAM resources. Oracle states that "The new sort algorithm shows more performance improvement for in-memory sorts.".

In a paper titled Advanced Management of Working Areas in Oracle 9i/10g", author Joze Senegacnik notes a new method for sorting in Oracle 10g release 2 and a hidden parameter called "_newsort_enabled" that turns-on the new sorting:  (the download password is network)

Oracle10gRw introduced a new sort algorithm which is using less memory and CPU resources [9],[10]. A hidden parameter _newsort_enabled = {TRUE|FALSE} governs whether the new sort algorithm will be used.

In Oracle 10g, disk sort reliability was also improved by using temporary tablespace groups.  In an article titled "Super-Sizing A Database: Oracle 10g Tablespace Enhancements", author Jim Czuprynski notes some common disk sorting problems:

"Temporary tablespaces can be the occasional bane of an Oracle DBA's existence. Since they are primarily used as sort work areas, when there are insufficient resources for sorting a result set directly in memory, it is not uncommon for a database to run out of space in a temporary tablespace at the most inopportune moments.

Oracle also uses temporary tablespaces to create and store an instance of each global temporary table (GTT) for each user session that invokes any PL/SQL using GTTs."

Czuprynski concludes that Oracle temporary tablespace groups help to limit (if not finally eliminate) out-of-space conditions for sort work areas during large aggregation and sorting operations.


Sorting enhancements in Oracle 10g release 2


This whitepaper titled "Sort Performance Improvements in Oracle Database 10g Release 2", we see that in-memory sorting (using the sort_area_size RAM PGA region) has been improved: 

"The improvements of the new sort implementation are significant: improved sort-performance of up to 5 times has been measured in lab conditions."

The paper also suggests that the new sorting helps with disk sort speed, but this may be due to the in-memory sort being faster before the sort spills out into the TEMP tablespace for a disk sort.  We also see that in-memory sorts are CPU-intensive, and that faster processors will also improve in-memory sort performance.

"The new sort algorithm also benefits from faster CPUs. You will see more performance improvements on a system with fast CPUs than you will on a system with slower CPUs."

To keep-up with research on the internals of the Oracle sorting improvements, try running this Google search to find 10gr2 sorting articles:


"oracle10g"|"oracle 10g" r2|"release 2" sort|sorting performance|improvements|improved

If you like Oracle tuning, see my latest book "Oracle Tuning: The Definitive Reference". 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts: 




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