Wednesday, October 25, 2017

Windows Cannot Install Required Files. Make sure all the files required for installation are available, and restart the installation. Error code: 0x8007025D


Windows Cannot Install Required Files. Make sure all the files required for installation are available and restart the installation. Error code: 0x8007025D

Usually, people connect this problem with media error - your installation source is corrupted. Microsoft and various guids recommend creating new installation CD or USB. In my case, it was my hard drive. I had to delete the partition and experiment with splitting original partition into smaller ones. The goal is to have one as big partition as possible that is healthy - because Program Files folder grows exponentialy :) It took me some time (in days) to finally get it right.

Friday, September 8, 2017

Floating point arithmetic in 21 century

I really hope that entire concept will be dropped one day. Current approach was useful 30 years ago, now we have much more memory and we can do it in a much better way. And yet when I look at JavaScript:
0.1 + 0.2 === 0.3 //false
(0.1 + 0.2) + 0.3 === 0.1 + (0.2 + 0.3) //false


It is all beacause of 0.1 representation in IEEE standard.
s eeeeeeee mmmmmmmmmmmmmmmmmmmmmmm    1/n
0 01111011 10011001100110011001101
           |  ||  ||  ||  ||  || +- 8388608
           |  ||  ||  ||  ||  |+--- 2097152
           |  ||  ||  ||  ||  +---- 1048576
           |  ||  ||  ||  |+-------  131072
           |  ||  ||  ||  +--------   65536
           |  ||  ||  |+-----------    8192
           |  ||  ||  +------------    4096
           |  ||  |+---------------     512
           |  ||  +----------------     256
           |  |+-------------------      32
           |  +--------------------      16
           +-----------------------       2
The sign is positive, that's pretty easy.

The exponent is 64+32+16+8+2+1 = 123 - 127 bias = -4, so the multiplier is 2-4 or 1/16.

The mantissa is chunky. It consists of 1 (the implicit base) plus (for all those bits with each being worth 1/(2n) as n starts at 1 and increases to the right), {1/2, 1/16, 1/32, 1/256, 1/512, 1/4096, 1/8192, 1/65536, 1/131072, 1/1048576, 1/2097152, 1/8388608}.

When you add all these up, you get 1.60000002384185791015625.

When you multiply that by the multiplier, you get 0.100000001490116119384765625, which is why they say you cannot represent 0.1 exactly as an IEEE754 float.

Wednesday, September 6, 2017

choreography vs orchestration

I see in more and more articles that authors are using both terms interchangeably. As far as I can tell there is no formal definition, just like with terms agile, microservices, SOA, but... in ancient days when I was studding computer science on a university there was a difference:
  • choreography: distributed decision making
  • orchestration: centralised decision making

Monday, September 4, 2017

JavaScript Exceptions vs. Errors

A JavaScript exception is a value that is thrown as a result of an invalid operation or as the target of a throw statement. While it is not required that these values are instances of Error or classes which inherit from Error, all exceptions thrown by Node.js or the JavaScript runtime will be instances of Error.

Some exceptions are unrecoverable at the JavaScript layer. Such exceptions will always cause the Node.js process to crash.

This is why you can write:
throw new Exception("foo bar");
throw "foo bar";

Tuesday, August 29, 2017

TPC-C current benchmarks for stateful and stateless services running Java.

  • Immediately consistency: 1 box: 2000 requests/second with 5 second response time
  • Eventually consistent: 1 box: 300 requests/second with a 100 millisecond response time.

It is all achivable, if you are not there you need tools to figure out why.
Switch to stateless services whenever possible. A great article about pushing the boundaries and how important it is in HFT is available in barbarians at the gateways.

Sunday, April 23, 2017

No versions found in startbootstrap-sb-admin-2.git

No versions found in https://github.com/IronSummitMedia/startbootstrap-sb-admin-2.git
The problem manifests itself because IronSummitMedia changed it's name to BlackrockDigital and you should go and install a different package from:
https://github.com/BlackrockDigital/startbootstrap-sb-admin-2