In-Memory OLTP Internals - Pro SQL Server Internals - page 667

Figure 32-26. Loading data to memory
A large percentage of deleted rows and, therefore, large delta files add unnecessary storage overhead and slow
down the data loading process. SQL Server addresses this situation with a process called merge . A background task
periodically analyzes if adjacent active data and delta files can be merged together in a way that active, non-deleted
rows from the merged data files would fit into a new data file.
In the example shown in Figure 32-25 , the first data file that covers the timestamp range of 1-1000 contains about
40 percent of the active rows. The second data file that covers the timestamp range of 1001-1650 has about 50 percent
of the active rows. Those files can be merged together to cover a timestamp of 1-1650. Figure 32-27 illustrates the data
and delta files after a merge.