Skip to main content

Comparing Optimization of Filtering in PowerShell

This morning in my Hunt Valley, MD PowerShell class, I extended yesterdays lesson (see yesterday’s post) into filtering optimization.  In the PowerShell world, we have a saying: “Filter to the Left”.  That means that you filter out as many objects as possible as close to the beginning of the piped commands as possible.  What we did was use the Get-EventLog cmdlet and filtered it in two ways.  We wanted to filter for Event ID 12.  In the Get-EventLog cmdlet, we used the InstanceID parameter with a value of 12.  In the second execution of Get-EventLog, we piped everything to Where-Object and filtered on the property InstanceID for a value of 12.  We then executed our code from yesterday to test the runtime for each one.

# Optimizing for Performance.

# Get-Help Get-EventLog -Parameter Newest

 

# Execute each section individually by highlighting

# the code and pressing F8.

Clear-History

 

# This is optimized

Get-EventLog -LogName System -InstanceId 12

 

# This is not Optimized

Get-EventLog -LogName System |

Where-Object InstanceID -eq 12

 

 

# Get the history information and execution times.

Get-History |

    Select-Object -Property CommandLine,

    @{N="ExecutionTime";

        E={($_.EndExecutionTime - $_.StartExecutionTime).TotalSeconds}} |

    Select-Object -Last 2

Here is the output from the fourth section.

CommandLine                                                                  ExecutionTime

-----------                                                                  -------------

Get-EventLog -LogName System -InstanceId 12                                      8.9346474

Get-EventLog -LogName System |...                                               14.6560631

You can see that the first command using its built in filtering capabilities is much faster than piping all the objects to Where-Object.

Comments

Popular posts from this blog

Adding a Comment to a GPO with PowerShell

As I'm writing this article, I'm also writing a customization for a PowerShell course I'm teaching next week in Phoenix.  This customization deals with Group Policy and PowerShell.  For those of you who attend my classes may already know this, but I sit their and try to ask the questions to myself that others may ask as I present the material.  I finished up my customization a few hours ago and then I realized that I did not add in how to put a comment on a GPO.  This is a feature that many Group Policy Administrators may not be aware of. This past summer I attended a presentation at TechEd on Group Policy.  One organization in the crowd had over 5,000 Group Policies.  In an environment like that, the comment section can be priceless.  I always like to write in the comment section why I created the policy so I know its purpose next week after I've completed 50 other tasks and can't remember what I did 5 minutes ago. In the Group Policy module for PowerShell V3, th

Return duplicate values from a collection with PowerShell

If you have a collection of objects and you want to remove any duplicate items, it is fairly simple. # Create a collection with duplicate values $Set1 = 1 , 1 , 2 , 2 , 3 , 4 , 5 , 6 , 7 , 1 , 2   # Remove the duplicate values. $Set1 | Select-Object -Unique 1 2 3 4 5 6 7 What if you want only the duplicate values and nothing else? # Create a collection with duplicate values $Set1 = 1 , 1 , 2 , 2 , 3 , 4 , 5 , 6 , 7 , 1 , 2   #Create a second collection with duplicate values removed. $Set2 = $Set1 | Select-Object -Unique   # Return only the duplicate values. ( Compare-Object -ReferenceObject $Set2 -DifferenceObject $Set1 ) . InputObject | Select-Object – Unique 1 2 This works with objects as well as numbers.  The first command creates a collection with 2 duplicates of both 1 and 2.   The second command creates another collection with the duplicates filtered out.  The Compare-Object cmdlet will first find items that are diffe

How to list all the AD LDS instances on a server

AD LDS allows you to provide directory services to applications that are free of the confines of Active Directory.  To list all the AD LDS instances on a server, follow this procedure: Log into the server in question Open a command prompt. Type dsdbutil and press Enter Type List Instances and press Enter . You will receive a list of the instance name, both the LDAP and SSL port numbers, the location of the database, and its status.