The Art of SQL Server FILESTREAM - Red Gate Software

Chapter 7: FILESTREAM Database Administrationcontains the record is still active, and will remain so until the log is backed up. EveryFILESTREAM operation is mapped to a transaction LSN in the transaction log. UnderFULL and BULK_LOGGED recovery models, the garbage collector will remove a file onlyafter the transaction log VLF that contains the LSN associated with the FILESTREAMoperation is not part of the active log.FILESTREAM garbage collection and tombstonetablesAs we have seen, SQL Server does not support in-place updates of FILESTREAM data. Ifwe modify a BLOB value stored in a FILESTREAM column, SQL Server will create a newdisk file with the modified value. The old file will stay around for some time until it is "nolonger needed" and the garbage collector steps in and deletes it.It is interesting to note how SQL Server keeps track of the garbage files. If we modify afew FILESTREAM data values and look into the FILESTREAM data folder, we'll find manymore files than the number of rows in the table. So the question is, "Which are garbagefiles and which are not?" SQL Server creates an internal table called the FILESTREAMtombstone table to hold the details of garbage files to be removed. The garbage collectorqueries this table to identify the garbage files and removes them when those files are nolonger needed.To see this in action, run the script in Listing 7-6 to create a sample database containing atable with two FILESTREAM columns.USE masterGOIF DB_ID('NorthPole') IS NOT NULLDROP DATABASE NorthPoleGO280