On Exadata (or when setting cell_offload_plan_display = always on non-Exadata) you may see the storage() predicate in addition to the usual access() and filter() predicates in an execution plan:
SQL> SELECT * FROM dual WHERE dummy = 'X';
Check the plan:
Display execution plan for last statement for this session from library cache...
SQL_ID dtjs9v7q7zj1g, child number 0
SELECT * FROM dual WHERE dummy = 'X'
Most people are relating direct path reads with an algorithm which is just controlling the way our read is performed. But actually in Exadata environment this is the algorithm which is balancing the load between the Compute and the Storage nodes. Something really important. As usual, the algorithm is not perfect and for some situations […]
If you try to find out what is HCC and how it works you could start reading the documentation, then some books, blog posts and at the end you will have to put all together. In this post I’ll do exactly this. Put all together. Starting with the basic and going through the internals with […]
One of the biggest advantages of Exadata are the Storage Indexes. Unfortunately Oracle is not providing us a lot of information about them and if you dig a bit in the net, you will find a lot creepy stories on how they are supposed to work. So instead of making yet another story, I’ll demonstrate […]
Oracle is trying to make everything automated, in general they are trying to reduce the administration. Nothing bad with that, but as we know the automated features in Oracle Database are good in most, but not in all situations. In those situations where the algorithms are not handling well, a human interaction is needed. The […]
Exadata X4 – Smart Flash Cache Compression – it’s Smart its Flash it’s Compression… So it shall be great, no? If you take a look at the Datasheet about this new feature you’ll notice something interesting: “zero performance overhead for compression and decompression”. Wow, now its even better! Smart, Flash, Compression, Zero Overhead! Lets see […]
I’ve previously written about a problem I encountered when kdump is configured to write to an NFS location with UEK (in Exadata software version 184.108.40.206.1). I’m please to report that the root cause of the problem has been identified and there is a very simple workaround.
There were some frustrating times working this particular SR, the most notable being a response that was effectively, “It works for me (and so I’ll (more...)
I seem to be getting a lot of surprising performance results lately on our X-2 quarter rack Exadata system, which is good – the result you don’t expect is the one that teaches you something new.
This time, I was looking at using a temporary tablespace based on flash disks (more...)
Oracle has released the much-anticipated version of cellsrv compatible with Oracle Database 220.127.116.11 (patch #16980054). Before thinking about upgrading, read MOS note #1571789.1 carefully. Unless you are planning to run database 12c on your Exadata, it would be advisable to continue down the 11.2 branch (more...)
Today, Oracle announced the Exadata X4-2 model. The X4 has some considerable improvements, namely:
- 12-core Intel Xeon e5-2697 CPUs, up from the 8-core models found in the X3-2 (hello, database licenses!)
- 256GB RAM per database server, upgradeable to 512GB
- 96GB RAM per storage server
- 800GB Sun Flash F80 cards (more...)
Exadata Maximum Availability Architecture from Yunus Emre Baransel
When the Smart Flash Cache was introduced in Exadata, it was caching reads only. So there were only read “optimization” statistics like cell flash cache read hits and physical read requests/bytes optimized in V$SESSTAT and V$SYSSTAT (the former accounted for the read IO requests that got its data from the flash (more...)
There were problems that affected UEK and NFS when 18.104.22.168.1 was initially released (as covered by Andy Colvin). As mentioned in the comments of Andy’s post: Oracle released an updated ISO with fixes for this problem (patch 16432033).
There were also problems with kdump not (more...)
Recently we noticed that imageinfo was displaying the following information at a customers site. Imageinfo was not displaying data i suspected, so a quick little blogpost about what was going on there.
[root@dm01db01 ~]# dcli -g /opt/oracle.SupportTools/onecommand/dbs_group -l root "imageinfo | grep 'Image version'"
dm01db01: Image version: 11.2. (more...)
Of all the claims I make about SSD for Oracle databases, the one that generates the most debate is that placing redo logs on SSD is not likely to be effective. I’ve published data to that effect in particular see Using SSD for redo on Exadata - pt 2 (more...)
Prior to storage server software version 22.214.171.124.0 (associated with Exadata X3), Exadata Smart Flash Cache was a “write-through” cache, meaning that write operations are applied both to the cache and to the underlying disk devices, but are not signalled as complete until the IO to the (more...)
Relational DBMS used to be fairly straightforward product suites, which boiled down to:
- A big SQL interpreter.
- A bunch of administrative and operational tools.
- Some very optional add-ons, often including an application development tool.
Now, however, most RDBMS are sold as part of something bigger.
With cellcli you can run the calibrate command, this will measure the performance of your harddisks and flashcards. It will eventually report to you the throughput and amount of IOPS that was measured during the calibrate, it will also report to you which luns are not performing up to par.
As part of my Cloud Control journey I encountered a strange problem where I got the following error for few Exadata Storage Server (cell) targets:
Metric evaluation error start - oracle.sysman.emSDK.agent.fetchlet.exception.FetchletException: em_error=Failed to execute_exadata_response.pl ssh -q -o ConnectTimeout=60 -o BatchMode=yes -o StrictHostKeyChecking=no -o (more...)