The function I mentioned crashes our upgrades to BC19 on a regular basis. - It lets the SQL Server run out of Memory (16GB) after about 12 Hours. on a single company with just 22k Items. The code in this upgrade codeunit doesn't look too bad, but is very inefficient as it loops every Items and reads the groups whenever an item has a Prod Group set instead of doing it the other way around

so my suggestion is to replace your current function with this:

procedure UpgradeItemPostingGroups()

var

  Item: Record "Item";

  GenProdPostingGroup: Record "Gen. Product Posting Group";

  InventoryPostingGroup: Record "Inventory Posting Group";

  UpgradeTagDefinitions: Codeunit "Upgrade Tag Definitions";

  UpgradeTag: Codeunit "Upgrade Tag";

begin

  if UpgradeTag.HasUpgradeTag(UpgradeTagDefinitions.GetItemPostingGroupsUpgradeTag()) then

    exit;

  GenProdPostingGroup.SetLoadFields(Code);

  if GenProdPostingGroup.FindSet() then

  repeat

    item.SetRange("Gen. Prod. Posting Group", GenProdPostingGroup.Code);

    Item.ModifyAll("Gen. Prod. Posting Group Id", GenProdPostingGroup.SystemId);

  until GenProdPostingGroup.Next() = 0;

  InventoryPostingGroup.SetLoadFields(Code);

  if InventoryPostingGroup.FindSet() then

  repeat

    item.SetRange("Inventory Posting Group", InventoryPostingGroup.Code);

    Item.ModifyAll("Inventory Posting Group Id", InventoryPostingGroup.SystemId);

  until InventoryPostingGroup.Next() = 0;

  UpgradeTag.SetUpgradeTag(UpgradeTagDefinitions.GetItemPostingGroupsUpgradeTag());

end;

p.s. the file you need to edit is found in \Upgrade\UpgradeBaseApp.Codeunit.al