This probably only is relevant for customers that run Oracle on big servers with lots of cores, like some of my clients that make use of the Exadata Xn-8 servers, like a X4-8 with 120 cores / 240 CPUs per node.
They recently came up with a re-write of a core application functionality. Part of this code did start the same code path for different data sets potentially several times concurrently ending up with many (more...)
It's probably not that well known that Oracle can actually rollback / re-start the execution of a DML statement should the cursor become invalidated. By rollback / re-start I mean that Oracle actually performs a statement level rollback (so any modification already performed by that statement until that point gets rolled back), performs another optimization phase
of the statement on re-start (due to the invalidation) and begins the execution of the statement from scratch. Note (more...)
As mentioned in the first
part of this instalment the different available distribution methods of the new parallel FILTER are selected automatically by the optimizer - in this last post of this series I want to focus on that optimizer behaviour.It looks like there are two new optimizer related parameters that control the behaviour of the new feature: "_px_filter_parallelized"
is the overall switch to enable/disable the new parallel filter capability - and (more...)
A new version 4.22 of the XPLAN_ASH utility is available for download.As usual the latest version can be downloaded here.
This version primarily addresses an issue with 12c - if the HIST mode got used to pull ASH information from AWR in 12c it turned out that Oracle forgot to add the new "DELTA_READ_MEM_BYTES" columns to DBA_HIST_ACTIVE_SESS_HISTORY - although it got officially added to V$ACTIVE_SESSION_HISTORY in 12c. So now I had to implement (more...)
Thanks to the many attendees that came to my presentation "Oracle 12c Parallel Execution New Features" at the DOAG conference 2015. You can download the presentation material here in Powerpoint
format, as well as check the Slideshare
Note that the Powerpoint format adds value in that sense that many of the slides come with additional explanations in the notes section.
If you are interested in more details I recommend visiting this post (more...)
Picking up from the first part
of this instalment I'll focus in this post on the available distribution methods for the new parallel FILTER subquery feature.In this post I won't go into the details how the optimizer selects the distribution method automatically - this will be covered in the last part.Here I merely describe the different available methods and how to control them using the new PQ_FILTER
hint, which is also mentioned in (more...)