The intention of this blogpost is to show the Oracle wait time granularity and the Oracle database time measurement granularity. One of the reasons for doing this, is the Oracle database switched from using the function gettimeofday() up to version 11.2 to clock_gettime() to measure time.
This switch is understandable, as gettimeofday() is a best guess of the kernel of the wall clock time, while clock_gettime(CLOCK_MONOTONIC,…) is an monotonic increasing timer, which means it is more precise and does not have the option to drift backward, which gettimeofday() can do in certain circumstances, like time adjustments via NTP.
The first thing I wanted to proof, is the switch of the gettimeofday() call to the clock_gettime() call. This turned out not to be as simple as I thought.
A recent posting on OTN presented a performance anomaly when comparing a parallel “insert /*+ append */” with a parallel “create table as select”. The CTAS statement took about 4 minutes, the insert about 45 minutes. Since the process of getting the data into the data blocks would be the same in both cases something was clearly not working properly. Following Occam’s razor, the first check had to be the execution plans – when two statements that “ought” to do the same amount of work take very different times it’s probably something to do with the execution plans – so here are the two statements with their plans:
First the insert, which took 45 minutes:
This is just a little example of thinking about hinting for short-term hacking requirements. It’s the answer to a question that came up on the Oracle-L listserver a couple of months ago (Oct 2015) and is a convenient demonstration of a principle that can often (not ALWAYS) be applied as a response to the problem: “I can make this query work quickly once, how do I make it work quickly when I make it part of a join ?”
The question starts with this query, which returns “immediately” for any one segment:
Here’s the latest video on my YouTube channel. This one is a quick run through of RDS for Oracle, a DBaaS offering from Amazon Web Services.
If you are not into the video thing, you can see the article this video was based on here.
Galo Balda has now joined the illustrious list of people who have said “.com” on one of my videos.
If you don’t want to read the story, the summary for this article is:
If you create bitmap join indexes on a partitioned table and you use partition exchanges to load data into the table then make sure you create the bitmap join indexes on the loading tables in exactly the same order as you created them on the partitioned table or the exchange will fail with the (truthful not quite complete) error: ORA-14098: index mismatch for tables in ALTER TABLE EXCHANGE PARTITION.
Today marks the 10th anniversary of Lex de Haan passing away. Although 10 years is a long time, I think about my dear friend Lex at least once a week. Lex assisted me adapting to new teaching skills when I progressed to blindness. It was Lex his idea to use colored magnets on my classroom […]
YesSQL Summit 2016 sponsored by O'Reilly and Axxana was held by the Northern California Oracle Users Group on January 26–28 at the Oracle conference center in Redwood City, California in conjunction with BIWA Summit 2016 and Spatial Summit 2016. The grand raffle prize sponsored by O'Reilly was a full pass to Strata + Hadoop World on March 28–31 in San Jose, California. Save 20% on Strata + Hadoop World conference passes with discount code UGNOCOUG. YesSQL Summit will return to the Oracle conference center on January 31, 2017.(read more)
RMOUG volunteers compile notifications of webinars, meetings, and meetups from the internet and post them here for everyone to use.
The information technology (IT) industry is always evolving and therefore always changing.
The latest video on my YouTube Channel is a run through of using the Database as a Service (DBaaS) offering on Oracle Cloud.
There have been a few minor changes in the interface since I last ran through capturing images, so the related article has been brought up to date.
I used my dad for the cameo in this video. Hopefully this will help him get a little more recognition, as he’s pretty much a nobody on the Oracle scene at the moment. With your help this could change!
This is just a short blog post about a simple DTrace script (dtrace_kghal_pga_code), that i recently wrote and published due to a PGA memory leak troubleshooting assignment. A client of mine noticed a major PGA memory increase after upgrading to Oracle 12c. The PL/SQL code did not change - just the database release. He already troubleshooted the issue with help of Tanel Poder's blog post "Oracle Memory Troubleshooting, Part 4: Drilling down into PGA memory usage with V$PROCESS_MEMORY_DETAIL" and identified the corresponding heap and allocation reason.