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...)
This post also applies to non-Exadata systems as hard drives work the same way in other storage arrays too – just the commands you would use for extracting the disk-level metrics would be different.
I just noticed that one of our Exadatas had a disk put into “predictive failure” mode (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...)
This post applies both to non-Exadata and Exadata systems.
Before Oracle 11.2 came out, it was true to say that Oracle Parallel Execution slaves always do direct path reads (bypassing buffer cache) when doing full segment scans. This should not be taken simplistically though. Even when you were doing (more...)
Prior to storage server software version 18.104.22.168.0 (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.
- Oracle has hugely thickened its (more...)
This is the fourth post on a serie of postings on how to get measurements out of the cell server, which is the storage layer of the Oracle Exadata database machine. Up until now, I have looked at the measurement of the kind of IOs Exadata receives, the latencies (more...)
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...)
Exadata is about doing IO. I think if there’s one thing people know about Exadata, that’s it. Exadata brings (part of the) processing potentially closer to the storage media, which will be rotating disks for most (Exadata) users, and optionally can be flash.
But with Exadata, you either do normal (more...)
When you are administering an Exadata or more Exadata’s, you probably have multiple databases running on different database or “computing” nodes. In order to understand what kind of IO you are doing, you can look inside the statistics of your database, and look in the data dictionary what that instance (more...)
Exadata gets its performance by letting the storage (the exadata storage server) participate in query processing, which means part of the processing is done as close as possible to where the data is stored. The participation of the storage server in query processing means that a storage grid can massively (more...)
The purpose of this post is to show what the wait event ‘cell smart table scan’ means, based on reproducible investigation methods.
First of all, if you see the ‘cell smart table scan’ event: congratulations! This means you are using your exadata how it’s intended to be used, which means (more...)
Having SQLTXPLAIN and SQLHC available, WHY do I need yet another way to display execution plans?
New script planx.sql reports execution plans for one SQL_ID from RAC and AWR. It is lightweight and installs nothing. It produces list of performance metrics for given SQL out of gv$sqlstats, gv$sqlstats_plan_hash, gv$sql and dba_hist_sqlstat. It also (more...)