Performance – The database stack

Bart Sjerps Oracle, Performance 4 Comments

hamb-stackAs mentioned before, I frequently find myself in discussions around Oracle performance and how an Oracle database behaves on EMC storage. It turns out that often there is a lot of confusion on how the different layers interact with each other and very few people seem to understand the whole stack.

So I started a personal challenge to make a “one picture tells more than 1000 words” complete overview of the Oracle on EMC database stack.

I failed.

Turns out it’s nearly impossible to get everything in one picture without cutting corners.

So here is a simplified (and therefore incorrect) picture. It ignores certain complexities and is far from complete, and might even contain errors.

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Wikipedia blackout

Bart Sjerps Various No Comments

Blackout
Just to inform you that tomorrow (wednesday jan. 18th, 2012), some of the links on my blog might not work due to Wikipedia’s one-day blackout, in protest against SOPA (and I use Wikipedia a lot as a great resource to learn from myself, and to point to my readers for more information on certain topics).

I think Wikipedia touches a true problem; governments (pushed by lobbyist groups) are pushing for an internet where you have to be cautious about what you say or publish. Best case, you might get blacklisted. Worst case? Figure it out for yourself.

I live in the Netherlands and currently something similar is going on about organizations trying to restrict people accessing certain information sources (in this case, the Pirate Bay). Whether Pirate Bay (or any other source of information for that matter) violates the law, or not, is (IMO) a different discussion. But if people (or organizations) want to restrict access by ordering ISP’s (information service providers, a.k.a. the mailman) to blacklist those sites (i.e. check your mail for offending content) instead of chasing the publishers of illegal materials of any kind, then we are well on our way to a different internet. An internet that is no longer free. I strongly oppose to that.

So, Wikipedia (and others), you have my full support.

Click the “STOP SOPA” banner (top right hand corner) if you want to learn more.

More info:

https://www.eff.org/deeplinks/2011/12/fight-blacklist-toolkit-anti-sopa-activists

https://www.eff.org/search/site/sopa

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Oracle and Data Integrity: Data in, Garbage Out?

Bart Sjerps Oracle 2 Comments

Stop Corruption

A trivial question:

What is the basic function of a storage system?
I would say, the trivial function of a storage system is to store digital data and getting it back when you need it.

To be specific:
get the data back exactly the way you stored it.

You would probably say “Duh, of course!”

A storage system (as simple as a hard disk or as sophisticated as an EMC VMAX) is supposed to store data and give it back unmodified. But recent research shows that simple disk drives are not as reliable as you might think. Enough material is available that explains why and how often disk drives fail to return the correct information, often without any error as if the corrupted data is perfectly valid. See below for more references to this issue.

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Application processing at lightning performance – The hourglass view of access times

Bart Sjerps Performance 2 Comments

HourglassEven in these modern times, when lots of things are changing in the ICT world, some lessons from the past still hold true.

Previously, I discussed the I/O stack in a typical database environment. As virtualization has complicated things a bit, the fundamental principles of performance tuning stay the same.

Recently I was browsing through old presentations of colleagues and found another interesting view on response times in an application stack. Again, I polished it up a bit and modified it to reflect a few innovations and personal insights.

The idea is as follows. We as humans have problems getting a feel of how fast modern microprocessors work. We talk in milliseconds, microseconds, nanoseconds. So – in the comparison we assume a 1 Gigahertz processor and then scale up one nanosecond to match one second – because this fits better in human’s view of the world. Then we compare various sorts of storage on the “indexed” timescale and see how they relate to each other.

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