Oracle database internals by Riyaj

Discussions about Oracle performance tuning, RAC, Oracle internal & E-business suite.

OOUG RAC day presentation files and scripts

Posted by Riyaj Shamsudeen on November 18, 2015

Thanks for coming to my presentations in RAC day at Dublin, Ohio. Please find the presentation files below. Hopefully, I will get video files and upload that here too.

OOUG presentation files and scripts

md5 checksum of the zip file is:


Posted in Oracle database internals, Performance tuning, Presentations, RAC | Tagged: , , | Leave a Comment »

RAC day with Ohio Oracle User Group

Posted by Riyaj Shamsudeen on October 22, 2015

I will be talking about RAC and performance in-depth, with lots of demos, in a RAC day training with Ohio Oracle User group on Nov 16,2015 Monday. Venue for the presentation is Dublin, Ohio.

Agenda for the day:

08:00a – 09:00: Registration / Breakfast

09:00a – 09:15: Announcements -Introduction of the speaker

09:15a – 10:30: Underpinning for Oracle RAC and Clusterware

10:30a – 10:45: Break

10:45a – 11:45: RAC cache fusion internals

11:45a – 01:00: Lunch

01:00p – 02:00: RAC Performance tuning Part 1 – Wait events and object tuning

02:00p – 02:15: Break

02:15p – 03:30: RAC performance tuning Part 2 – locks, library cache locks etc.

03:30p – 03:45: Member Announcements, Gift Drawings

Please RSVP to the co-ordinators so that you will have a seat :)


Posted in Oracle database internals, Performance tuning, Presentations, RAC | Tagged: , , , | 1 Comment »

Demos do fail.

Posted by Riyaj Shamsudeen on April 15, 2015

I am an ardent believer of “show me how it works” principle and usually, I have demos in my presentation. So, I was presenting “Tools for advanced debugging in Solaris and Linux” with demos in IOUG Collaborate 2015 in Las Vegas on April 13 and my souped-up laptop (with 32G of memory, SSD drives, and an high end video processor etc ) was not responding when I tried to access folder to open my presentation files.

Sometimes, demos do fail. At least, I managed to complete the demos with zero slides :-) Apologies to the audience for my R-rated rants about laptop issues.

You can download presentations files from the links below.



Posted in in-memory, inmemory, Performance tuning, Presentations | Tagged: , , , , , | Leave a Comment »

IOUG Collaborate 2015

Posted by Riyaj Shamsudeen on March 25, 2015

I will be presenting two topics in IOUG Collaborate 2015 in Vegas. Use the show planner and add my presentations to your schedule :)

Session #189: April 13 Monday 9:15 to 10:15AM Topic: Oracle Database 12c In-Memory Internals. Room Palm B

Session #145: April 13 Monday 12:45PM-1:45PM Topic: Tools and Techniques for Advanced Debugging in Solaris & Linux (mostly live demo). Room Palm B.

Posted in inmemory, Oracle database internals, Performance tuning, Presentations, RAC | Tagged: , , , , , | Leave a Comment »

RMOUG Training Days 2015

Posted by Riyaj Shamsudeen on January 19, 2015

I will be talking in Rocky Mountain Oracle User Group Training Days 2015(, with live demos (hopefully there will be no failures in the demo). My topics are:

Feb 17: Deep dive: 3:15PM to 5:15PM – RAC 12c optimization: I will discuss RAC global cache layer in detail with a few demos. You probably can’t find these deep Global Cache layer details anywhere else :)

Feb 19: Wednesday: 2:45PM to 3:45PM – Advanced UNIX tools: I will discuss both Solaris and Linux advanced tools to debug deep performance issues.

Feb 19: Wednesday: 12:15PM – 1:15PM – Exadata SIG panel with Alex Fatkulin.

Come to Denver. Come on, it won’t be cold ( I think :) )

Uploading presentation and scripts of the presentation files: RMOUG_2015_Riyaj_RAC_12c_optim files

Presentation files for Unix tools demos: RMOUG_2015_Riyaj_Unix_tools

Posted in 11g, 12c, Presentations, RAC | Tagged: , , , | 1 Comment »

In-memory pre-population speed

Posted by Riyaj Shamsudeen on October 6, 2014

While presenting at Oaktable World 2014 in San Fransisco, I discussed the in-memory pre-population speed and indicated that it takes about 30 minutes to 1 hour to load ~300GB of tables. Someone asked me “Why?” and that was a fair question. So, I profiled the in-memory pre-population at startup.

Profiling methods

I profiled all in-memory worker sessions using Tanel’s snapper script and also profiled the processes in OS using Linux perf tool with 99Hz sample rate. As there is no other activity in the database server, it is okay to sample everything in the server. Snapper output will indicate where the time is spent; if the time is spent executing in CPU, then the perf report output will tell us the function call stack executing at that CPU cycle. Data from these two profiling methods will help us to understand the root cause of slowness.

  1. @snapper.sql out,gather=stw 600 10 “select sid from v$session where program like ‘%W00%'”
  2. Perf tool : perf record -F 99 -u oracle -g sleep 3600

continue reading

Posted in 12c, in-memory, inmemory, Oracle database internals, Performance tuning, Presentations | Tagged: , , , , , , , | Leave a Comment »

Oaktable world 2014 is on!

Posted by Riyaj Shamsudeen on September 26, 2014

Many Oaktable members are planning to talk about deep technical topics in Oaktable world 2014. Looking at the agenda, I am excited, so many deep topics are planned. I will be talking about in-memory internals on Monday morning at 9AM, 9/29/2014, right after Mogens’ Keynote speech. You can find all details here: Oaktable world 2014. I will post my presentation slides after the presentation.

Start your open world week presentation with mine :). Sorry, no beers planned at that time, it is 9AM, after all!

Thanks for attending my presentation at Oaktable World 2014. You can download the slides : In-memory_internals.pdf.

Also, our book Expert Oracle RAC 12c has been translated to Chinese language. You can find details about that book in one of the translator’s blog: Alex lizx.

Posted in 12c, in-memory, inmemory | Tagged: , , | Leave a Comment »

inmemory: Why did that table was not populated in the column store?

Posted by Riyaj Shamsudeen on September 11, 2014

I enabled an huge 70G table for inmemory population, I expected the inmemory population to take a while, but the population didn’t complete even after letting it run for a day. Why?

ASH data

Initial review of the server shows no issues, no resource starvation. This must be a problem with Oracle processes itself. I started digging further, and ASH data shows that in numerous samples the process was seen reading block using single block I/I calls. Also object_id matches with the table I was trying to populate.

   select * from (
    select start_time, end_time, sql_id,event, current_obj#,  cnt_on_cpu + cnt_waiting tot_cnt,
  	rank () over ( order by (cnt_on_cpu + cnt_waiting) desc ) rnk
    from  (
  	  min(start_time) start_time,
  	  max(end_time)   end_time,
  	  sum(decode(session_state,'ON CPU',1,0))  cnt_on_cpu,
 	  sum(decode(session_state,'WAITING',1,0)) cnt_waiting
     ( select
 	first_value(sample_time) over( order by sample_time ) start_time,
 	last_value(sample_time) over( order by sample_time
 				rows between unbounded preceding and unbounded following ) end_time,
 	sql_id,event, session_state, current_obj#
 	     (select * from v$active_session_history ash where session_id= &&sid and session_serial#=&&serial_number)
   group by sql_id, event, current_obj#
  where rnk 
------------------------- ------------------------- ------------- ------------------------------ ------------ ---------- ----------
18-AUG-14 AM 18-AUG-14 AM		  db file sequential read	       168967	     990	  1
												       168967	     156	  2
								  direct path read		       168967	      50	  3
						    bdwtqttka2w2y					   -1	       3	  4
						    bdwtqttka2w2y direct path read		       168967	       1	  5
						    24uqc4aqrhdrs				       168967	       1	  5
													   -1	       1	  5

Read the rest of this entry »

Posted in 12c, inmemory | Tagged: , | 3 Comments »

inmemory: sa00 process

Posted by Riyaj Shamsudeen on September 11, 2014

After the restart of a 12c inmemory database with 300GB+ SGA, I noticed that an Oracle background process sa00 was consuming a bit of CPU. Documentation suggests that it is SGA Allocator process, however, ipcs -ma command shows that the shared memory segment is already allocated. I was curious, of course, what would that background process will be allocating?.


Process stack of the process shows that it is touching SGA pages to pre-page SGA memory pages.

$ pstack 21131
#0  0x0000000000d9996e in ksmprepage_memory ()
#1  0x0000000000d99369 in ksm_prepage_sga_seg ()
#2  0x0000000003a5c78b in skgmapply ()
#3  0x0000000000da686a in ksmapply_v2 ()
#4  0x0000000000d9a82c in ksmprepage ()
#5  0x0000000000d99f89 in ksm_sslv_exec_cbk ()
#6  0x0000000000f79810 in ksvrdp ()
#7  0x00000000031013b7 in opirip ()
#8  0x0000000001bb0a08 in opidrv ()
#9  0x00000000026c0f71 in sou2o ()
#10 0x0000000000bbd85e in opimai_real ()
#11 0x00000000026cb6bc in ssthrdmain ()
#12 0x0000000000bbd72c in main ()

$ ps -ef|grep  21131
oracle   21131     1 96 15:00 ?        00:01:50 ora_sa00_XXXXXX

Two notable changes in this area:
1. Incidentally, pre_page_sga initialization parameter was defaulted to a value of FALSE until 11.2. In version 12.1, the parameter value defaults to TRUE.
2. As huge SGA is expected for inmemory databases, a new background process SA00 is also created to touch all SGA memory pages at startup.

As inmemory worker processes will be populating the inmemory column store soon after the startup, touching memory pages at instance startup makes sense, and the feature should improve the performance of inmemory population. At least, Worker processes doesn’t need to suffer from huge amount page faults. (note that this SGA is not using hugepages).

Change to the parameter pre_page_sga also should improve the performance of inmemory scan, as the memory map entries will be setup at the process startup. However, I am not quite clear, how this change will affect the performance of a connection storm, i.e. if there are numerous database connections in a short period of time and disconnects. Isn’t that the reason why the pre_page_sga was defaulted to FALSE? But, I need to test this thoroughly to understand the implications further.

Posted in 12c | Tagged: , , , | Leave a Comment »

Inmemory: Not all inmemory_size is usable to store tables.

Posted by Riyaj Shamsudeen on September 11, 2014

I have been testing the inmemory column store product extensively and the product is performing well for our workload. However, I learnt a bit more about inmemory column store and I will be blogging a few them here. BTW, I will be talking about internals of inmemory in Oaktable world presentation, if you are in the open world 2014, you can come and see my talk:


Inmemory_size initialization parameter determines the amount of memory allocated to the in-memory column store. But only 80% of that memory value is allocated to store the objects. For examples, if you set inmemory_size=272G, then only 217G (=272*0.8) is used to store the objects, and the remaining 55GB is allocated for inmemory journal and internal objects. This is the reason why the inmemory heap is also split and tagged: IMCA_RO and IMCA_RW. IMCA_RW seems to be storing inmemory journal and IMCA_RO is to store objects in the memory. (Previous statement is not completely validated yet).

SELECT mem inmem_size,
       tot disk_size,
       (tot/mem) compression_ratio,
       100 *((tot-bytes_not_pop)/tot) populate_percent
  (SELECT SUM(INMEMORY_SIZE)/1024/1024/1024 mem,
    SUM(bytes)              /1024/1024/1024 tot ,
    SUM(bytes_not_populated)/1024/1024/1024 bytes_not_pop
   FROM v$im_segments
---------- ---------- ------------- ----------------- ----------------
    217.25     231.17           .00        1.06407869              100

So, you should plan accordingly when you enable inmemory option. Notice that the compression ratio is about 1, but, that is because these objects are already compressed using HCC compression and so, memory compression is not going to give us a better compression. However, I see that size of a few objects have increased in-memory compared to the disk size, but, I am hoping that will be considered as a bug and will be fixed in later release.

Unfortunately, inmemory area chunks are not visible in v$sgastat at all, but v$sga shows the inmemory area correctly (show SGA output is correct as it queries v$sga too).

Posted in 12c, Oracle database internals, Performance tuning | Tagged: , , , , | Leave a Comment »


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