Ghost Record Cleanup Process
When rows are deleted from an index leaf page, the space is not released
immediately, instead SQL Server marks those records as "ghost records" (records
pending for deletion). Later the Ghost Record Cleanup Process will remove
those records physically in an asynchronous fashion, improving the performance
of the delete operations.
The Ghost Record Cleanup Process has also an impact on the insert operation.
SQL Server allocates new pages when there is no room for data in the existing
pages. They incur in pages split, moving 50% of the rows form the filled up
pages to the newly allocated pages. SQL Server mark the records moved from
the filled pages as "ghost records", which are later removed by the Ghost Record