Oracle database internals by Riyaj

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

Posts Tagged ‘RAC performance’

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 »

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 »

Golden rules of RAC performance diagnostics

Posted by Riyaj Shamsudeen on March 20, 2014

After collaborating with many performance engineers in a RAC database, I have come to realize that there are common pattern among the (mis)diagnosis. This blog about discussing those issues. I talked about this in Hotsos 2014 conference also.

Golden rules

Here are the golden rules of RAC performance diagnostics. These rules may not apply general RAC configuration issues though.

  1. Beware of top event tunnel vision
  2. Eliminate infrastructure as an issue
  3. Identify problem-inducing instance
  4. Review send-side metrics also
  5. Use histograms, not just averages

Looks like, this may be better read as a document. So, please use the pdf files of the presentation and a paper. Presentation slide #10 shows indepth coverage on gc buffer busy* wait events. I will try to blog about that slide later (hopefully).

Golden rules of RAC diagnostics paper

Golden rules of rac diagnostics ppt

Scripts mentioned in the presentation can be downloaded here.


Posted in 11g, Performance tuning, Presentations, RAC | Tagged: , , , , , | 3 Comments »

RAC Internals: cached sequences and 12c

Posted by Riyaj Shamsudeen on September 9, 2013


I blogged about DFS lock handle contention in an earlier blog entry. SV resources in Global Resource Directory (GRD) is used to maintain the cached sequence values. I will further probe the internal mechanics involved in the cached sequences. I will also discuss minor changes in the resource names to support pluggable databases (version 12c).

SV resources

Let’s create an ordered sequence in rs schema and then query values from the sequence few times.

create sequence rs.test_seq order cache 100;
select rs.test_seq.nextval from dual; -- repeated a few times.

Sequence values are permanently stored in the seq$ dictionary table. Cached sequence values are maintained in SV resources in GRD and SV resource names follows the naming convention to include object_id of the sequence. I will generate a string using a small helper script and we will use that resource name to search in the GRD.

    ||trim(TO_CHAR(object_id, 'xxxxxxxx'))
    || trim(TO_CHAR(0,'xxxx'))
    || '],[SV]' res
FROM dba_objects WHERE object_name=upper('&objname')
     AND owner=upper('&owner') AND object_type LIKE 'SEQUENCE%'
Enter value for objname: TEST_SEQ
Enter value for owner: RS

Read the rest of this entry »

Posted in 12c, Oracle database internals, Performance tuning, RAC, weird stuff | Tagged: , , , , , | 2 Comments »

Book: Expert Oracle RAC 12c

Posted by Riyaj Shamsudeen on September 8, 2013

A quick note, Expert Oracle RAC book co-written by me is available now: Expert Oracle RAC 12c. I have written about 6 chapters covering the RAC internals that you may want to learn :) I even managed to discuss the network internals in deep, after all, network is one of the most important component of a RAC cluster.

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

Reverse Path Filtering and RAC

Posted by Riyaj Shamsudeen on June 1, 2012

This is a quick note about reverse path filtering and impact of that feature to RAC. I encountered an interesting problem recently with a client and it is worth blogging about it, with a strong hope that it might help one of you in the future.


Environment is GI, Linux 5.6. In a 3 node cluster, Grid Infrastructure (GI) comes up cleanly in just one node, but never comes up in other nodes. If we shutdown GI in first node, we can start the GI in second node with no issues. Meaning, GI can be up in just one node at any time.

System Admins indicated that there are no major changes, only few bug fixes. Seemingly, problem started after those bug fixes. But there were few other changes to the environment /init.ora parameter change etc. So, the problem was not immediately attributable to just OS changes.

Read the rest of this entry »

Posted in Oracle database internals, Performance tuning, RAC | Tagged: , , , , , , | 11 Comments »

All about RAC and MTU with a video

Posted by Riyaj Shamsudeen on May 22, 2012

Let’s first discuss how RAC traffic works before continuing. Environment for the discussion is: 2 node cluster with 8K database block size, UDP protocol is used for cache fusion. (BTW, UDP and RDS protocols are supported in UNIX platform; whereas Windows uses TCP protocol).

UDP protocol, fragmentation, and assembly

UDP Protocol is an higher level protocol stack, and it is implemented over IP Protocol ( UDP/IP). Cache Fusion uses UDP protocol to send packets over the wire (Exadata uses RDS protocol though).

MTU defines the Maximum Transfer Unit of an IP packet. Let us consider an example of MTU set to 1500 in a network interface. One 8K block transfer can not be performed with just one IP packet  as the IP packet size (1500 bytes) is less than 8K. So, one transfer of UDP packet of 8K size is fragmented to 6 IP packets and sent over the wire. In the receiving side, those 6 packets are reassembled to create one UDP buffer of size 8K. After the assembly, that UDP buffer is delivered to an UDP port of a UNIX process. Usually, a foreground process will listen on that port to receive the UDP buffer.

Read the rest of this entry »

Posted in 11g, Oracle database internals, Performance tuning, Presentations, RAC, video | Tagged: , , , , , , , , , , , , , , , , , , | 11 Comments »


Posted by Riyaj Shamsudeen on April 29, 2012

We know that database blocks are transferred between the nodes through the interconnect, aka cache fusion traffic. Common misconception is that packet transfer size is always database block size for block transfer (Of course, messages are smaller in size). That’s not entirely true. There is an optimization in the cache fusion code to reduce the packet size (and so reduces the bits transferred over the private network). Don’t confuse this note with Jumbo frames and MTU size, this note is independent of MTU setting.

In a nutshell, if free space in a block exceeds a threshold (_gc_fusion_compression) then instead of sending the whole block, LMS sends a smaller packet, reducing private network traffic bits. Let me give an example to illustrate my point. Let’s say that the database block size is 8192 and a block to be transferred is a recently NEWed block, say, with 4000 bytes of free space. Transfer of this block over the interconnect from one node to another node in the cluster will result in a packet size of ~4200 bytes. Transfer of bytes representing free space can be avoided completely, just a symbolic notation of free space begin offset and free space end offset is good enough to reconstruct the block in the receiving side without any loss of data.This optimization makes sense as there is no need to clog the network unnecessarily.

Read the rest of this entry »

Posted in 11g, Oracle database internals, Performance tuning, RAC | Tagged: , , , | 9 Comments »


Posted by Riyaj Shamsudeen on April 19, 2012

If you are attending Collaborate 2012, you might be interested in my content-rich sessions below :

Session Number: 326
Session Title: SCAN, VIP, HAIP, and other RAC acronyms
Session Date/Time/Room: Tue, Apr 24, 2012 (10:45 AM – 11:45 AM) : Surf C

Session Number: 327
Session Title: Internals and Performance Boot Camp: Truss, pstack, pmap, and more
Session Date/Time/Room: Wed, Apr 25, 2012 (03:00 PM – 04:00 PM) : Palm A

Hope to see you there!

Update: I am uploading presentation files. Presentations are much more recent than the document :-)


Thanks for attending!

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


Get every new post delivered to your Inbox.

Join 258 other followers