When observing  a DBCC DHRINKDATABASE on the DMV sys.dm_exec_requests  command column , you’ll notice different commands appearing.

Step 1 – DbccSpaceReclaim   - Prepares for data moves by cleaning up space –e.g deferred allocations and manage empty extents

Step 2 – DbccFileCompact - Adjusting pages beyond the target to before the target.

Step 3 – DbccLOBCompact - LOB data compact

 Sometimes it may appear the command is taking a long time. Some reasons may be:

1) If a heap is moved all Non Clustered index physical link references to a record number on a data page need to be updated. If there are large NonClustered Indexes , the Query Processor  needs to process all the updates.

2)  Analyse for other processes blocking the lock required to move the page SQL Server – Current queries executing on SQL Server

3)  Analyse IO subsystem

Read More

SQL Server – How to Predict the DBCC SHRINKDATABASE finish time

SQL Server - Monitoring a Rollback and sys.dm_exec_requests ...

SQL Server Storage and IO performance - SQL Server DBA