The most efficient way to a lot of transaction in SharePoint is using of method. For deleting operations there are . Code exaple from that post:

 

 

    

//

 We prepare a String.Format with a String.Format, this is why we have a {

{0}} 

   

string command = String.Format(

"

<Method><SetList Scope=\"Request\">{0}</SetList><SetVar Name=\"ID\">{

{0}}</SetVar><SetVar Name=\"Cmd\">Delete</SetVar><SetVar Name=\"owsfileref\">{

{1}}</SetVar></Method>

", list.ID);

   

//

 We get everything but we limit the result to 100 rows 

   SPQuery q = 

new SPQuery();

   q.RowLimit = 

100;

   

//

 While there's something left 

   

while (list.ItemCount > 

0)

   {

    

//

 We get the results 

    SPListItemCollection coll = list.GetItems(q);

    StringBuilder sbDelete = 

new StringBuilder();

    sbDelete.Append(

"

<?xml version=\"1.0\" encoding=\"UTF-8\"?><Batch>

");

    Guid[] ids = 

new Guid[coll.Count];

    

for (

int i=

0;i<coll.Count;i++)

    {

     SPListItem item = coll[i];

     sbDelete.Append(

string.Format(command, item.ID.ToString(), item.File.ServerRelativeUrl));

     ids[i] = item.UniqueId;

    }

    sbDelete.Append(

"

</Batch>

");

    

//

 We execute it 

    web.ProcessBatchData(sbDelete.ToString());

    

//

We remove items from recyclebin

    web.RecycleBin.Delete(ids);

    list.Update();

   }

  }

 

 

[System.Reflection.Assembly]::Load(

"

Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c

")

[System.Reflection.Assembly]::Load(

"

Microsoft.SharePoint.Portal, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c

")

[System.Reflection.Assembly]::Load(

"

Microsoft.SharePoint.Publishing, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c

")

[System.Reflection.Assembly]::Load(

"

System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a

")

write-host 

# Enter your configuration here

$siteUrl = 

"

http://mysharepointsite.example.com/

"

$listName = 

"

Name of my list

"

$batchSize = 

1000

write-host 

"

Opening web at $siteUrl...

"

$site = 

new-

object Microsoft.SharePoint.SPSite($siteUrl)

$web = $site.OpenWeb()

write-host 

"

Web is: $($web.Title)

"

$list = $web.Lists[$listName];

write-host 

"

List is: $($list.Title)

"

while ($list.ItemCount -gt 

0)

{

  write-host 

"

Item count: $($list.ItemCount)

"

  $batch = 

"

<?xml version=`

"

1.0`

"

 encoding=`

"UTF-

8`

"

?><Batch>

"

  $i = 

0

  

foreach ($item 

in $list.Items)

  {

    $i++

    write-host 

"

`rProcessing ID: $($item.ID) ($i of $batchSize)

" -nonewline

    $batch += 

"

<Method><SetList Scope=`

"Request`

"

>$($list.ID)</SetList><SetVar Name=`

"ID`

"

>$($item.ID)</SetVar><SetVar Name=`

"Cmd`

"

>Delete</SetVar><SetVar Name=`

"owsfileref`

"

>$($item.File.ServerRelativeUrl)</SetVar></Method>

"

    

if ($i -ge $batchSize) { 

break }

  }

  $batch += 

"

</Batch>

"

  write-host

  write-host 

"

Sending batch...

"

  # We execute it 

  $result = $web.ProcessBatchData($batch)

  write-host 

"

Emptying Recycle Bin...

"

  # We remove items 

from recyclebin

  $web.RecycleBin.DeleteAll()

  write-host

  $list.Update()

}

write-host 

"

Done.

"