Wednesday, May 25, 2011

ORA-27303: additional information: requested interface failed bind. Check output from ifconfig command

Finally on the exadata, and I make a simple mistake in the login script. 

First I logon to the exadata, and I can start and stop the default database. Everything looks fine.  I then go to create my own database and I get this message

ORA-27504: IPC error creating OSD context

ORA-27300: OS system dependent operation:bind_fail failed with status: 0
ORA-27301: OS failure message: Error 0
ORA-27302: failure occurred at: skgxpvifconf
ORA-27303: additional information: requested interface failed bind. Check output from ifconfig command

Huh ?  We are having issues transferring files to the machine also (scp's are stalling). so this looks like a network issue right ?  Check output from ifconfig, bind failed for an IP address.. all network related clues.

Well the issue turned out to be ORA_CRS_HOME set incorrectly.    Once I set it correctly, I am able to start up a new database, and start my dbduplicate process.

I just wanted to pass this along, and hopefully help someone else who get's this cryptic message.

Tuesday, May 24, 2011

Extended RAC vs Golden Gate

 Every so often this question comes up... "Why don't we do extended RAC ?"


Well here is some of my answer as to what we need to consider.

First, Extended RAC is setting up a RAC cluster across datacenters.. Each datacenter has it's own independent Storage arrays. Some Nodes are placed on one datacenter (a) and some are placed in (b). To keep it simple and for redundancy, lets say there is 2 nodes in each datacenter (4 total). These 4 nodes are all part of the same cluster, and they all share the same Global cache. Disk writes are mirrored across datacenters. This means that all writes are synchronous, and the write must be acknowledged on both arrays (in both datacenters).. Dark fiber is a must to accomplish this.

Issues ? There are number of concerns this brings up.


1) The global cache is shared across the datacenters. Any latency is felt by any processing that requires sharing data between clusters in opposite datacenters. This can cause some performance degradation.

2) Writes are synchronous across datacenters. This can increase the write time for any disk writes.

3) You are not protected against logical corruption, upgrade outages etc.

Best practice is to also have a physical standby for HA, and to allow patching etc (transient logical), etc.


In the end you end up with twice as much equipment, twice as much storage, and a lot more complex system over just keeping a physical standby database. It is even recommended that your quorum is kept in a third datacenter.

The cost doubles, and the complexity doubles. The question you need to ask is.. is it worth all this ?

Another option is to utilize Golden Gate. Golden gate gives you similar flexibility by going active-active across datacenters. You still need to have a physical standby, but the advantage of GG over Extended RAC is that the physical does not have to be the same class server or storage ($$). The whole point of the physical is to keep the changes so that they can be sent to the other active cluster.. The standby cluster never becomes a a client available primary.


I would summerize the 2 choices as follows


Extended RAC

  • Guaranteed synchronous write across datacenters.


  • Less availability for any database changes requiring shutdown (parameter or patching).
  • Greater latency when data is sent between datacenters.
  • BCP requires full size footprint
Golden Gate



  •  Database available for any database changes requiring downtime.
  •  Application releases can be applied in a rolling fasion
  •  Smaller footprint for BCP servers
  •  Less lattency for reads and commits (though latency for data availabilty)


  • Database updates are asynchronous. There will be a delay before update is visible in other datacenter (< 2 seconds)


Neithor one of these will guarantee 99.999% uptime, but GG comes a lot closer. With extended RAC, there is more planned downtime because it is a single database.
As you can see the decision should be driven by how important it is for the application to be able to have the data immediately available for read across datacenters. If you can tolerate the < 2 second latency, GG is a better product. If the application can't tolerate the latency Extended RAC is only viable solution.

Oracle and networking latency with small packets

Recently I have run into some performance issues, and trying to track down the cause has been a challenge.  It wanted to share a valuable lesson that I learned.

It started like any other performance issues.  The phone rings, and the database is slow.  Why do they think the database is slow ? Because the app isn't very busy, and the processing isn't moving along at the expected pace.  This is a new app, and they are in beta.  The process goes along as it always does.  Check the database for any bottlenecks, or any performance issues.  The database all looks good.  The queries are all executing in milliseconds. on the new hardware.  The application looks good.  The process is executing in Milliseconds, and then calling out to the database for the next query.  Everything looks good, database is fast, application is fast.  The issue goes to the networking group, and the network group concludes that we have a nice 1ge going between the 2 servers.  The network isn't breaking a sweat.  The issue continues.

So what was the issue ?  It was the number of hops, and the distance of the hops between the application and the database server.  It turns out that this is a chatty app, and it sends a lot of small packets back and forth between the database server, and the app server. 
To make matters worse, the application was just uplifted to new hardware for both the database, and the application.  This uplift caused the applications to be less of a bottleneck, pushing the bottleneck to the network.

The issue turned out to be network latency.  Not a lot of latency, (just a couple of milliseconds), but enough to be noticable for a very chatty application.  It becomes more, and more noticable as servers become faster.  Now that queries run in < 0.00ms, the network is popping up as more of a bottleneck.

The lesson I want to pass on, is that I would highly suggest you measure the network latency, and know how much of a impact it has.. Especially if you going across datacenters, or across many networks in the same datacenters.

My test was a simple one..

1) Create a script full of "select 'x' from dual;

2) put a !date call at the beging and end of the script

3) Run this on a client on your network and compare the difference between the begin and the end time.

4) Run this for multiple scenarios.. I even ran it as IPC, to find out what the network overhead is.

Knowing the expected latency as you go across your datacenter(s) is useful to find out where that missing time is going. So often, it is blamed on the dba (database), and doing this kind of check will let you know what isn't the database.