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.
Posts Tagged ‘oracle performance’
Posted by Riyaj Shamsudeen on September 8, 2013
Posted by Riyaj Shamsudeen on August 29, 2012
There are many questions from few of my clients about asmlib support in RHEL6, as they are gearing up to upgrade the database servers to RHEL6. There is a controversy about asmlib support in RHEL6. As usual, I will only discuss technical details in this blog entry.
ASMLIB is applicable only to Linux platform and does not apply to any other platform.
Now, you might ask why bother and why not just use OEL and UK? Well, not every Linux server is used as a database server. In a typical company, there are hundreds of Linux servers and just few percent of those servers are used as Database servers. Linux system administrators prefer to keep one flavor of Linux distribution for management ease and so, asking clients to change the distribution from RHEL to OEL or OEL to RHEL is always not a viable option.
Do you need to use ASMLIB in Linux?
Short answer is No. Long answer is possibly No. ASMLIB is an optional support library and eases the administration of ASM devices. Especially, it is helpful while adding new devices to the nodes in a cluster. ASMLIB essentially stamps the devices and so, it is easily visible in other nodes of a cluster in the next asm scandisk. asmlib also provides device persistence, which is the important benefit of ASM (see the discussion below for more details about device persistence).
Posted by Riyaj Shamsudeen on August 18, 2012
Just a quick note, I will be presenting on “Truss, pstack, pmap, and more” talking about advanced UNIX utilities and how it can be utilized to understand inner working of an application or even Oracle Database Engine.
My timeslot is between 2:15 and 3:15 in Room 2016.
Uploading presentation files. Thanks for attending at OOW12.
Posted by Riyaj Shamsudeen on June 15, 2012
Quick note about Jonathan Lewis trip to Dallas: Jonathan Lewis will be presenting two day seminar on two topics, “Beating the Oracle Optimizer” (June 28) and “Troubleshooting and tuning” (June 29th).
The event will be held June 28-29, 2012 at SMU-in-Legacy in Plano, TX.
This is a must-attend event for experienced DBAs and Developers. Especially, if you are planning to upgrade your database/application in the near-future or if you are in the middle of an upgrade, you must attend these two seminars. This seminar series provide enormous value resolving complex Production performance issues.
Click Here for details.
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.
Posted in 11g, Oracle database internals, Performance tuning, Presentations, RAC, video | Tagged: cache fusion mtu, fragmentation and reassembly, gc lost packets, ipfrag_high_thres, ipfrag_low_thres, ipfrag_time, Jumbo frames, MTU, MTU=9000, oracle performance, RAC internals, RAC performance, RAC presentations, RAC training, RAC video, RAC videos, RDS, UDP vs tcp, wireshark | 12 Comments »
Posted by Riyaj Shamsudeen on April 19, 2012
Last week (March 2012), I was conducting Advanced RAC Training online. During the class, I was recreating a ‘gc buffer busy’ waits to explain the concepts and methods to troubleshoot the issue.
Let’s define these events first. Event ‘gc buffer busy’ event means that a session is trying to access a buffer,but there is an open request for Global cache lock for that block already, and so, the session must wait for the GC lock request to complete before proceeding. This wait is instrumented as ‘gc buffer busy’ event.
From 11g onwards, this wait event is split in to ‘gc buffer busy acquire’ and ‘gc buffer busy release’. An attendee asked me to show the differentiation between these two wait events. Fortunately, we had a problem with LGWR writes and we were able to inspect the waits with much clarity during the class.
Remember that Global cache enqueues are considered to be owned by an instance. From 11g onwards, gc buffer busy event differentiated between two cases:
- If existing GC open request originated from the local instance, then current session will wait for ‘gc buffer busy acquire’. Essentially, current process is waiting for another process in the local instance to acquire GC lock, on behalf of the local instance. Once GC lock is acquired, current process can access that buffer without additional GC processing (if the lock is acquired in a compatible mode).
- If existing GC open request originated from a remote instance, then current session will wait for ‘gc buffer busy release’ event. In this case session is waiting for another remote session (hence another instance) to release the GC lock, so that local instance can acquire buffer.
Following output should show the differentiation with much clarity.
Posted by Riyaj Shamsudeen on February 13, 2012
Temporary tablespaces are shared objects and they are associated to an user or whole database (using default temporary tablespace). So, in RAC, temporary tablespaces are shared between the instances. Many temporary tablespaces can be created in a database, but all of those temporary tablespaces are shared between the instances. Hence, temporary tablespaces must be allocated in shared storage or ASM. We will explore the space allocation in temporary tablespace in RAC, in this blog entry.
In contrast, UNDO tablespaces are owned by an instance and all transactions from that instance is exclusively allocated in that UNDO tablespace. Remember that other instances can read blocks from remote undo tablespace, and so, undo tablespaces also must be allocated from shared storage or ASM.
Space allocation in TEMP tablespace
TEMP tablespaces are divided in to extents (In 11.2, extent size is 1M, not sure whether the size of an extent is controllable or not). These extent maps are cached in local SGA, essentially, soft reserving those extents for the use of sessions connecting to that instance. But, note that, extents in a temporary tablespace are not cached at instance startup, instead instance caches the extents as the need arises. We will explore this with a small example:
Posted in 11g, Oracle database internals, Performance tuning, RAC | Tagged: CI enqueue, DFS lock handle, oracle performance, RAC performance, SS enqueue, temporary tablesapce, temporary tablespace, temporary tablespace groups | 16 Comments »
Posted by Riyaj Shamsudeen on February 10, 2012
I just uploaded my presentation materials for ‘Truss, pstack etc’ for HOTSOS 2012 symposium , a performance intensive conference, happening right here in my home town Dallas, TX.
I can’t believe, it is been ten years from the start of this annual conference! This is the tenth annual symposium and I have been presenting in this symposium for almost all years except few early years. Quality of presentations and quality of audience is very high in this symposium and many of the audience are repeat audience, almost this feels like an annual pilgrimage to “sanctum of performance”. If you are interested in learning the techniques and methods to debug and resolve performance issues in a correct way, you should definitely consider attending this symposium. To top it off, Jonathan Lewis is conducting Training Day this year.
There are many great authors talking in this symposium.
Let me take this opportunity to welcome you to Dallas and encourage you to attend this symposium !
PS: Mark Bobak has been presenting or attending all ten years of this symposium, kudos Mark! And, Yes, that’s the same Mark Bobak who is the list admin for that most famous oracle-l mailing list.
PPS: Even though I live in Texas, no, I do not ride an horse to commute, instead, I drive a Ford Mustang car.(Incidentally, Mustang means “a small breed of horse, often wild or half wild, found in the southwestern US” as defined by dictionary.com, So, after all, I am driving a string of wild horse).
Posted by Riyaj Shamsudeen on February 10, 2012
I will be leaving to Denver in few days to talk about the following presentations in RMOUG 2012. Stop by and say hello to me if you intend to attend RMOUG training days.
My sessions in RMOUG 2012 are
- Room 402:Session 2: Parallel Execution in RAC – Wednesday 10:45 AM to 11:45AM
- Room 4f: Session 10: Troubleshooting RAC background processes – Thursday 1:30PM to 2:30PM
- Room 4f: Session 11: A kind and Gentle introduction to RAC – Thursday 2:45 PM to 3:45 PM
Hope to see you there.