Sitecore Tackled

I need to get items from a big bucket.
For best performance you should get the items through Sitecore ContentSearch.

Here I have some example code how to get a selection of items from a bucket.
Let’s say I want to get items that has a specific Tag on a field, which in this case is a string type field. (You can of course change the queryable to whatever you like)

List<Item> ResultsItems = new List<Item>();
IIndexable index = new SitecoreIndexableItem(bucketItem);

using (var context = ContentSearchManager.GetIndex(index).CreateSearchContext())
{
   var results = 
     context.GetQueryable<T>().Where(x => x.TagFieldName.Equals("TagName"))).GetResults();
   
   foreach (var result in results)
   {
     Item item = result.Document.GetItem();
     if(item !=null)
     {
       ResultsItems.Add(item);
     }
   }
}

Now ResultsItems are filled with the item context of all the children of the bucket.

Note: I’m showing the code for demonstration purpose. Beware of potentially calling a GetItem() on potential thousands of items.
I would also recommend selecting the fields you are after with .Select(i => new { i.FieldA, i.FieldB}) (read more here) so that the query gets smaller.