Counting Without Counts

Ewald Cress discusses the breferences member:

I’ll spare you my false starts, but I think I finally have it. The first observation is that, on the occasions breferences increments, it does not increment linearly, but instead has an exponential growth pattern. These increments take it through the sequence 0, 1, 3, 7, 15, 31, 127, 255 etc. Or in binary: 0, 1, 11, 111, 1111, 11111, 111111, 1111111, 11111111…

Those numbers can be seen as off-by-one variations of powers of two. Forget the offset, and think of the number as simply doubling on each increment if it keeps your head clearer – instead of accuracy, we have a order-of-magnitude reference count.

I’d never heard of an algorithm like this, although that could be due to my having dealt with relatively little low-level structural code.  I’m glad Ewald sussed out the mechanics driving breferences.

Related Posts

The Bitmap Operator

Hugo Kornelis describes a new operator: The Bitmap operator is used to build a bitmap that, based on a hash, represents which values may be present in a data flow. Due to the chance of hash collisions in the hash function used, the Bitmap process can produce false positives but not false negatives – so a match based on […]

Read More

Visualizing Merge Joins

Bert Wagner continues his series on physical join operators: The base algorithm works as follows: SQL Server compares the first rows from both sorted inputs.  It then continues comparing the next rows from the second input as long as the values match the first input’s value.Once the values no longer match, SQL Server increments the […]

Read More

Categories

September 2016
MTWTFSS
« Aug Oct »
 1234
567891011
12131415161718
19202122232425
2627282930