ze blog of simon

Brand: Union hand-roasted
Bean: sumatra, extra fancy
Region/Producer: Gayo Mountain Co-Operative, Aceh.
Roast:
Grind: Cafetière

Test brew: Espresso
Test Equipment: Kenwood Cremissimo

Full bodied, deep rich taste, minimal bitter aftertaste, but not overly sweet. Very impressed. 4/5

I’m just back from the Open Source Solution Centre’s Information Evening at the Seagoe Hotel, Daniel Bled has obviously worked hard at sharing his passion for open source software, he and the rest of the team from Southern Regional College & InvestNI put on an evening they should be proud of.  Daniel did a sterling job of trying to convey the Open Source philosophy to the gathered non-technical, business oriented audience.  He focused on:

1. Open Source – the source code is available for all to view.
2. Open Licensing – zero licensing costs for using the software, although support costs.
3. Open Access – your data isn’t locked away.
4. Open To Change – you have the source code, you can make it fit your needs.

I’m paraphrasing all of this as I didn’t take notes and this is all from memory – Daniel please feel free to correct me.  I’m sure Stallman & Co would be spitting blood by now, but Daniel’s pitch seemed to strike home with the audience, I think The Four Fundamental Freedoms would have been lost on them in the 10min Daniel had.

After a substantial meal, we had a talk from an InvestNI representative who attempted to convince us that the current economic environment is tough, but we have some come through tougher aspects in the last few decades, and he did a fairly good job – the outlook is gloomy, but a lack of confidence will only make things worse.  He repeated a comment I have heard before, “the project was good last month, it’ll be good next month, if it makes sense, do it.  Don’t let the bad outlook on the news put you off”.  Here here.

The next stage was a little more depressing, the idea was for local businesses who have worked with the OSSC to talk about there experiences & benefits, unfortunately Bowman Group’s Marketing & Sales Director couldn’t resist a captive audience and squandared the bulk of the time to tell us all about the group and what great windows they make.  Luckily their HR & IS manager was more direct & to the point, explaining that data lock-in, a lack of flexibility & rocketing costs helped them select SugarCRM as their CRM platform, helping them track there sales process and possibly even drive part of their manufacturing processes.

Next up was one of the owners of a local HR outsourcing firm, it was a similar story of meeting with Daniel and Daniel & his team helping them use SugarCRM to manage there growing list of prospects, customers, projects and related tasks.  The speaker put across her point well, explaining that even her as a non-technical user could see the benefits and use the software easily.

A brief wrap up from Daniel was followed by the usual attempt at a panel Q&A session, which failed miserable as they usually do in this part of the world.

What I’m looking forward to next is discovering what the next step is for the Open Source Solution Centre is, how do we in the Open Source community enagage with the OSSC and how do local businesses do the same.

The Open Source Solution Centre are running an information evening at the Seagoe Hotel, Portadown on Monday 30th March 2009, there’s more info here and here. I hope attend and help convey what open source can do for business users and what the tangible benefits and advantages are. There is more information about the Open Source Solution Centre here. You can find more about Job Done Right, my open source consultancy and advice service here.

1. We both fluffed our vows, he fluffed his inauguration vow, I fluffed my wedding vow, only one is on the web for the world to see
2. there is no 2.

The NHS gets a lot of flack from all sorts of sources, and the media tend to delight in hi-lighting the terrible experiences people have had with the NHS, including horror stories about people being left in trolleys in A&E, people not being able to get access to Doctors out of hours

Over Christmas, my 15 month old daughter caught a nasty virus/cold that knocked her for six, and we ended up calling our local surgery out-of-hours. Several times.  Our surgery participates in the local out-of-hours scheme, where there is a central number to call, they take your details & a Doctor calls you back.  On each occasion we had a call back within the hour.  On each occasion the Doctor was friendly & helpful.  On each occasion we ended up taking Zoe to the out-of-hours clinic to be checked, after being given a specific appointment time.  

1. One the first visit, we were seen almost exactly on time, given a prescription and told which chemist near us was open and able to complete the prescription.  We had the visit, prescription fulfilled and were on our way home within the hour.  This was on a Sunday 28th December.
2. Our second visit, we were seen within 10min of our time slot, given a slightly stronger antibiotic, which the Doctor made up there & then as it was late and we wouldn’t be able to find an open chemist until the morning.
3. The third visit was much the same, seen within 10min of the time slot, Zoe was thoroughly checked over & we were advised to finish the current course of medication.

The out-of-hours clinic is 15min from our house, there’s plenty of parking, the staff are friendly, the staff there are who the out-of-hours telephone number goes to.  

Craigavon Area Hospital & Lurgan Medical Practice, hats off to you, your system works, you were there when we needed you and you delivered a service you should be proud of.  I for one am glad that my income tax is being spent wisely.

More noise needs to be made when the NHS does something right, constant negativity is only self fulfilling.

I’m fully aware that this was fairly simple primary care, and that things get a lot more complex with serious medical conditions, but that why I choose to pay for medical insurance that covers these major things.  Having a service that’s available 24 hours during the holidays when you have a sick child is a mind saver, if not a life saver.

More unmissible stuff from @stephenfry Stephen Fry in America (BBC Micro Site)

Episode 1: New World

Episode 2: Deep South

Episode 3: Misssissippi

Episode 4: Mountains and Plains

Episode 5: True West

Episode 6: ?

I had an interesting challenge in work recently, we have 3 data centres running our applications, currently the RR DNS system does what it’s supposed to, spreads the data round each of the 3 DCs evenly.  This works fine when all of your data centres have a similar capacity.  But ours don’t.  This causes problem when your load/traffic gets to the point where one of the DCs can’t cope.  Now, there are many expensive and complicated solutions to this, this how ever isn’t one of them, it’s quite simple, has it’s weaknesses, but as you’ll see it’s also quite elegant.

Background

Our infrastructure already relies heavily on MySQL replication & PowerDNS, both of those are installed on all our public machines, indeed, we have a large MySQL replication loop with many spokes off the loop, ensuring that all of the MySQL data is available everywhere.  PowerDNS is used for both internal & external DNS services, all backed off the MySQL backend on the aforementioned MySQL replication loop.  This is important to us, as this solution required no new software, just some configuration file tweaks & same database table alterations.

Overview

Each record is assigned a weight. This weight will influence the likelihood of that record being returned in a DNS request with multiple A records. A weight of 0 will mean that the record will always be in the set of A records returned. A weight of 100 will mean that the record will never be returned (well, almost never).

Method

1. Add an extra column to the PowerDNS records table, called weight, this is an integer.
2. Create a view on the records table that adds random values to each record every time it is retrieved.
3. Alter the query used to retrieve data from the records table to use the view and filter on the weight and random data to decide if the record should be returned.

This is achieved by using the view to create a random number between 0 and 100 (via rand()*100).

create view recordsr AS select content,ttl,prio,type,domain_id,name, rand()*100 as rv, weight from records;

We use this SQL to add the column:

alter table records add column `weight` int(11) default 0 after change_date;

The random data is then compared against the record weight to decide if the record should be returned in the request. This is done using the following line in the pdns.conf file:

gmysql-any-query=select content,ttl,prio,type,domain_id,name from recordsr where name=’%s’ and weight < rv order by rv

For small sample sets (100), the results are quite poor & the method proves to be inaccurate, but for larger sets, 10,000 and above, the accuracy improved greatly.  I’ve written some scripts to perform some analysis against the database server & against the DNS server itself.  To test the DNS server, I set cache-ttl=1 and no-shuffle=on in pdns.conf.  With the cache-ttl=1, I waited 1.1 seconds between DNS queries.

Here’s some results, sample-pdns.pl was used to gather this data:

Sample Size = 1,000

#### WRR DNS Results
dc1: 462, 46.2% (sample size), 23.38% (total RR)
dc2: 514, 51.4% (sample size), 26.01% (total RR)
dc3: 1000, 100% (sample size), 50.60% (total RR)
total_hits: 1976, 197.6% (sample size), 100% (total RR)

Desired priorities were:
dc1 2/100, 80%
dc2 5/100, 50%
dc3 0/100, 100%

Sample Size = 10,000

#### WRR DNS Results
dc1: 10000, 100% (sample size), 50.57% (total RR)
dc2: 5821, 58.21% (sample size), 29.43% (total RR)
dc3: 3952, 39.52% (sample size), 19.98% (total RR)

pos-1-dc1: 5869, 58.69% (sample size), 29.68% (total RR)
pos-1-dc2: 2509, 25.09% (sample size), 12.68% (total RR)
pos-1-dc3: 1622, 16.22% (sample size), 8.20% (total RR)
pos-2-dc1: 3332, 33.32% (sample size), 16.85% (total RR)
pos-2-dc2: 2548, 25.48% (sample size), 12.88% (total RR)
pos-2-dc3: 1540, 15.4% (sample size), 7.78% (total RR)
pos-3-dc1: 799, 7.99% (sample size), 4.04% (total RR)
pos-3-dc3: 790, 7.9% (sample size), 3.99% (total RR)
pos-3-dc2: 764, 7.64% (sample size), 3.86% (total RR)

total_hits: 19773, 197.73% (sample size), 100% (total RR)

#### Desired priorities were:
dc3 60/100, 40%
dc2 40/100, 60%
dc1 0/100, 100%

As you can see, with the larger sample size, the weighting becomes much more transparent.

dc1 appeared in the returned records 100% of the time, as expected, dc2 appeared 58.21% (desired percentage was 60%) and dc3 appeared 39.52% (desired percentage was 40%).

What is possibly more interesting & relevant is the number of times a particular dc appears in the top slot (pos-1) of the returned results, this is the A record most likely to be used by the client.  dc1 appears in the top slot 58.69% of the time, with dc2 appearing 25.09% and dc3 16.22%.  These results diverge from the desired prioroties quite a bit, but are still in order with the desired distribution.

Advantages

1. No new code/binaries to distribute
2. Reuse existing infrastructure
3. Easy to roll-back from.

Disadvantages

1. Fairly coarse grained controls of load balancing (no feedback loop)
2. At least 1 site should have a weight of 0
3. No gurantee on number of records that will be returned in a query (other then records with a weight of 0)
4. Increased load on the database generating 1 or more random numbers on each query against the view