cell flash cache read hits vs. cell writes to flash cache statistics on Exadata

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...)

Hard Drive Predictive Failures on Exadata

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...)

Kdump to NFS Broken in UEK

There were problems that affected UEK and NFS when 11.2.3.2.1 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...)

Info about Exadata’s imageinfo and rpm’s

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...)

When do Oracle Parallel Execution Slaves issue buffered physical reads – Part 2?

In the previous post about in-memory parallel execution I described in which cases the in-mem PX can kick in for your parallel queries.

A few years ago (around Oracle 11.2.0.2 and Exadata X2 release time) I was helping a customer with their migration to Exadata X2. Many (more...)

When do Oracle Parallel Execution Slaves issue buffered physical reads – Part 1?

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...)

Redo on SSD: effect of redo size (Exadata)

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...)

Exadata Write-back cache and free buffer waits

Prior to storage server software version 11.2.3.2.0 (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...)

RDBMS and their bundle-mates

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.

Exadata – a new learning cuvrve

Perhaps I might be touch late on adopting/exploring/reacting/coping up with the exadata, but, it was always my dream and passion to work with the technologies since the announcement. As we knew Exadata is not something we can download and configure that easily on PC like those of traditional database or (more...)

Exadata: disk level statistics

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...)

About cellcli calibrate

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.

(more...)

Why my EM12c is giving Metric evaluation error for Exadata cell targets?

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: measuring IO latencies experienced by the cell server

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...)

System Statistics Gathered in Exadata Mode – When Are They Relevant?

The aim of this post isn’t to explain what the “exadata mode” is. Hence, if you don’t know what it is, before continuing reading have a look to this post published on Kerry Osborne’s blog. The only think I would like to add is that the “exadata mode” is available (more...)

My #OOW13 Session: Are Indexes Unnecessary in Exadata

Thanks to all those who came to my session "Are Indexes Unnecessary in Exadata" at Oracle Open World 2013. Considering it was late afternoon of the last day of the conference, especially after the appreciation concert, it was a pleasure to see a packed room. Judging by the interaction I (more...)

Skalare Subqueries in der WHERE clause

Vor neunundzwanzig Tagen hat Tanel Poder seinen Artikel Scalar Subqueries in Oracle SQL WHERE clauses (and a little bit of Exadata stuff too) veröfffentlicht und ehe der aus meinem reader verschwindet, sollte ich dazu ein paar Notizen machen.
  • eine scalar subquery in der WHERE clause hat die Form: WHERE ... = (more...)

Stuck Timezone Upgrades and Smart Scans

I heard a strange report from a client late last week - they weren't getting any smart scans on their Exadata - a data warehouse, no less (and we checked to see if cell_offload_processing was set to true).  Queries would run normally, but for some reason, the "cell physical IO (more...)

Virtualization on Exadata?

A while back, I noticed this session in the Open World 2013 content catalog.  I didn't think much of it at the time, other than that it had a catchy title.  The other day, I downloaded the latest Exadata deployment utility via the OneCommand tool.  I noticed something a little (more...)

Analyzing page allocation failures on Exadata

I have seen several clients who are struggling to decode page allocation failures on Exadata, in this post i will try to explain how to read the backtrace. The following is an anonymized client case where page allocation failures are leading up to a node reboot.

Jan 1 11:58:02 dm01db01  (more...)