René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Poor Performance in Foreach -Parallel","articleBody":"It was reported here https://github.com/PowerShell/PowerShell-RFC/pull/194 by @Ayanmullick  \r\nthat\r\n\r\n\u003e The below script runs faster without -parallel than with.\r\n\u003e \r\n```\r\n(Get-WinEvent -ListLog * -EA SilentlyContinue).Where({$PSItem.recordcount -ne '0'}).Logname|\r\n                ForEach-Object -Parallel {Get-WinEvent -FilterHashtable @{logname = \"$PSItem\";Starttime ='8/24/2019 11:00:00';Endtime ='8/24/2019 11:09:00';Level=1,2,3} -EA SilentlyContinue }\r\n```\r\n\u003e It took 18 secs to finish with -parallel and only 5 without.\r\n\r\nThomas Lee put up this case where it was slower. https://twitter.com/doctordns/status/1164461929093566465\r\n\r\n**It is understood that  parallelizing trivial code in will more overhead than the time saved**\r\n\r\nUsing Start-Parallel from the PowerShell Gallery I ran this to ping every machine on my local subnet. 200 addresses are not used, so in sequence it would take 800-1000 seconds. \r\n\r\n`1..254 | Start-Parallel -Scriptblock {param ($P) ping \"192.168.0.$p\" -n 1 | where {$_ -match \"ttl=\"}} -MaxThreads 300`\r\n\r\nit took **9 seconds**\r\n\r\nThe new equivalent is\r\n`1..254 | foreach -Parallel {ping \"192.168.0.$_\" -n 1 | where {$_ -match \"ttl=\"}} -ThrottleLimit 300`\r\n\r\nWhich takes **31 seconds**; I would expect broadly similar performance with the cmdlet slightly faster. \r\n\r\nUsing threadjob which ships with PS 6 and 7 I created this \r\n```\r\n$j = 1..254 | foreach {  \r\n   $sb=[scriptblock]::Create(\"ping -n 1 192.168.0.$_ | where {`$_ -match 'TTL=' } \")                                    \r\n    Start-ThreadJob -ScriptBlock $sb -ThrottleLimit 300 }\r\n while ($j.state -eq \"running\" -or $j.hasmoredata -eq $true) {\r\nforeach ($finished in $j.where({$_.state -eq \"completed\"})){ receive-job -Id $finished.id; }                       } \r\n\r\n```\r\nWhich runs in 11 seconds.\r\nThe cmdlet should be doing something very similar to this but not taking 3 times as long\r\n\r\n\r\n\r\n\r\n\r\n","author":{"url":"https://github.com/jhoneill","@type":"Person","name":"jhoneill"},"datePublished":"2019-08-27T09:12:04.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/10450/PowerShell/issues/10450"}