Understanding Neural Networks: Perceptrons

Akash Sethi explains what a perceptron is:

In machine learning, the perceptron is an algorithm for supervised learning of binary classifiers. It is a type of linear classifier, i.e. a classification algorithm that makes its predictions based on a linear predictor function combining a set of weights with the feature vector.
Linear classifier defined that the training data should be classified into corresponding categories i.e. if we are applying classification for the 2 categories then all the training data must be lie in these two categories.
Binary classifier defines that there should be only 2 categories for classification.
Hence, The basic Perceptron algorithm is used for binary classification and all the training example should lie in these categories. The basic unit in the Neuron is called the Perceptron.

Click through to learn more about perceptrons.

Uses Of kd-trees

Sandipan Dey explains what a kd-tree is and how it works:

The prime advantage of a 2d-tree over a BST is that it supports efficient implementation of range search and nearest-neighbor search. Each node corresponds to an axis-aligned rectangle, which encloses all of the points in its subtree. The root corresponds to the entire plane [(−∞, −∞), (+∞, +∞ )]; the left and right children of the root correspond to the two rectangles split by the x-coordinate of the point at the root; and so forth.

  • Range search: To find all points contained in a given query rectangle, start at the root and recursively search for points in both subtrees using the following pruning rule: if the query rectangle does not intersect the rectangle corresponding to a node, there is no need to explore that node (or its subtrees). That is, search a subtree only if it might contain a point contained in the query rectangle.

  • Nearest-neighbor search: To find a closest point to a given query point, start at the root and recursively search in both subtrees using the following pruning rule: if the closest point discovered so far is closer than the distance between the query point and the rectangle corresponding to a node, there is no need to explore that node (or its subtrees). That is, search a node only if it might contain a point that is closer than the best one found so far. The effectiveness of the pruning rule depends on quickly finding a nearby point. To do this, organize the recursive method so that when there are two possible subtrees to go down, you choose first the subtree that is on the same side of the splitting line as the query point; the closest point found while exploring the first subtree may enable pruning of the second subtree.

  • k-nearest neighbors search: This method returns the k points that are closest to the query point (in any order); return all n points in the data structure if n ≤ k. It must do this in an efficient manner, i.e. using the technique from kd-tree nearest neighbor search, not from brute force.

Sandipan implements a fairly classic problem in this space:  the behavior of a group of flocking birds.

The Decline(?) Of Google Search

Vincent Granville argues that Google search is on a slow decline:

What has happened over the last few years is that many websites are now getting most of their traffic from sources other than Google. Google is no longer the main source of traffic for most websites, because webmasters pursue other avenues to generate relevant traffic, in particular social networks and newsletter – as it is easier to attract the right people and promote the right content through these channels. Think about this: How did you discover Data Science Central? For most recent members, the answer is not Google anymore. In that sense, Google has lost its monopoly when it comes to finding interesting information on the Internet. The reason is that Google pushes more and more search results from partners, their own products, possibly content that fits with its political agenda, big advertisers, old websites, big websites, and web spammers who find a way to get listed at the top. In the meanwhile, websites such as ours promote more and more articles from little high quality publishers and great bloggers that have a hard time getting decent traffic from Google. For them, we are a much bigger and better source of traffic, than Google.

I think this is a fairly optimistic view of the situation, as there’s a difference between “I want to learn about a topic” versus “I want to learn this specific thing.”  I think Vincent’s argument is much stronger on the former, but when it comes to the latter, the first thing I hear people say is that they’re googling it.

Synchronizing Availability Group Objects

Derik Hammer has a process to maintain logins, backup devices, linked servers, SQL Agent details, and more between Availability Group nodes:

A notable limitation of this process is that it does not update existing objects. Jobs which already exist but were updated, will not be altered. I chose to omit that functionality because it presents merge complications and problems. For example, the cleanest way to handle the process would be to drop and create the object each time the synchronization runs. If that happened, however, there would be gaps when logins didn’t exist and applications would fail to connect, SQL Agent jobs would lose history, and/or the processing of a job would fail because it was dropped part way through executing.

With that limitation aside, this is a very interesting process and I recommend giving it a careful read.  Derik also includes the Powershell script at the end.

Getting Fancier With VM Creation

Raul Gonzalez shows how to spin up a Hyper-V VM using Powershell:

There are a lots of command to create or manipulate VM’s and I’m still only scratching the surface, but although I’m not a PS person, I have to admit that every time I want to do something, I find relatively easy to find a powershell command or a script for it, so I like it.

For instance, creating new virtual machines it’s a simple as one command

New-VM

And that’s only the beginning, we can add the different virtual hardware like in the UI, Drives, Network Adapters and so on. And then configure memory, CPU and NUMA, etc…

This is the script which I’m more or less running to create my VM’s, this in particular will be a Hyper-V Host itself, so there are a couple of interesting settings I’ll tell you about later.

Click through for Raul’s script.

Checking Availability Group Status With Powershell

Tracy Boggiano shows off a script which checks Availability Group status of selected servers:

My favorite thing to automate using PowerShell is checking on the status of things on multiple servers.  For example, after patching your environment running a quick query to make sure the version number is the same.  In this example, we will use a cmdlet my coworker wrote in combination in my cmdlet to check the health of all the Availability Groups across our landscape or you could use it just check one.  After all I do consider myself to be an HA/DR nut.

I’ve blogged about my coworker’s Get-CmsHost cmdlet before but now he has and shared it on github so you can read more about here.

In my cmdlet I use the same code that used in the SSMS AG dashboard to check the status of my Availability Groups.

Tracy includes her cmdlet as well as several example calls.

Considerations With Third-Party Backup Tools

Gianluca Sartori gives us a laundry list of potential problems with third-party database backup solutions:

2. Potentially dangerous separation of duties
Backup tools are often run and controlled by windows admins, who may or may not be the same persons responsible for taking care of databases. Well, surprise: if you’re taking backups you’re responsible for them, and backups are the main task of the DBA, so… congrats: you’re the DBA now, like it or not.
If your windows admins are not ok with being the DBA, but at the same time are ok with taking backups, make sure that you discuss who gets accountable for data loss when thing go south. Don’t get fooled: you must not be responsible for restores (which, ultimately, is the reason why you take backups) if you don’t have control over the backup process. Period.

There is plenty of sound advice in this post.  These points also apply to roll-your-own solutions as well, but the main focus is on enterprise backup tools, which are in many cases surprisingly shoddy.

Powershell And CMS

Mark Wilkinson loves Powershell and he loves Central Management Servers and he loves combining the two:

Get-CmsHosts is a function I wrote as part of a custom PowerShell module we maintain internally at my employer. It is simple to use, but is the base of most automation projects I work on.

Simple Example

PS> Get-CmsHosts -SqlInstance 'srv-' -CmsInstance srv-mycms-01

This example will connect to srv-mycms-01 and return a distinct list of instance host names registered with that CMS server that start with the string srv-. This output can then be piped to other commands:

Read on for more examples and details, and then grab the script at the end of Mark’s post.

Disabling Named Pipes Using Powershell

Brian Carrig shows how to disable the Named Pipes protocol using Powershell:

Windows and POSIX systems both support something referred to as “named pipes”, although they are different concepts. For the purposes of this post I am referring only to the Windows version. By default on most editions of SQL Server (every edition except Express Edition), there are three supported and enabled protocols for SQL server to listen on – Shared Memory, TCP/IP and Named Pipes. The inclusion of named pipes has always confused me somewhat. In theory, named pipes allow communication between applications without the overhead of going through the network layer. This advantage disappears when you want to communicate over the network using named pipes. In all modern versions of SQL Server, named pipes does not support Kerberos, so for most shops you likely will not be using or should not be using named pipes to communicate with SQL Server.

Security best practices dictate that if you are not using a particular protocol, you should disable it. There is an option to disable this is in the GUI in Configuration Manager but since this T-SQL Tuesday blog post is about using Powershell it does not make sense to cover it here. Nor is it particular easy to use the GUI to make a configuration change across hundreds of SQL instances. Unfortunately, I have not found a good way to make this change that does not involve using WMI, if anybody is aware of a better method, I welcome your feedback.

Read the whole thing.  You should have Named Pipes enabled if you’re running a NetBIOS network.  But because it’s not 1997 anymore, you probably shouldn’t be running a NetBIOS network.

Spinning Up Hyper-V VMs With Powershell

Andrew Pruski shows us how to enable Hyper-V and create a Windows VM using Powershell:

I’m constantly spinning up VMs and then blowing them away. Ok, using the Hyper-V GUI isn’t too bad but when I’m creating multiple machines it can be a bit of a pain.

So here’s the details on the script I’ve written, hopefully it could be of some use to you too.

Click through for the script; it’s ultimately just a few lines of code.

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