Automatic migration at PcVue startup
It is strongly recommended that you take a full backup of your databases before launching your application with a new version of PcVue.
During startup, the HDS checks its databases’ structures.
The migration process consists in:
- Changing the log and trend table structures
- Re-building the indexes of these tables
As these operations can take some time, the HDS will convert them automatically during the first start-up of your application if the total size of all your databases is less than 10 GB.
In such a case, you will see the following message in the event viewer indicating that the database structures and data are being migrated. 
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This operation can take a few minutes. Interrupting this process by stopping or killing the PcVue or HDS processes or hard-stopping the computer can lead to corrupted and unrecoverable data.
Typical durations as seen during internal qualification and beta testing are as follow:
| Database size | Migration duration |
| 1 GB | 1 mn 30 sec |
| 10 GB | 30 mn |
| On a computer with 4 GB of RAM and a Core2Duo E6750@2,66GHz CPU | |
If the total size of all your databases is over 10 GB, the migration will not be processed automatically and the HDS will refuse to start.
In such a case, you will see the following message in the event viewer indicating that the HDS failed to start:
Event viewer message: HDS didn't start normally. Please read HDS log file
HDS.log file message: Unable to run HDS compatibility treatment on databases (files are too big): use manual scripts
The HDS.log file can be found in the following folder:
SVInstallDir\Bin\Log files\HDS.log
Where SVInstallDir is the installation directory of PcVue.
In this situation, you have to run the Transact-SQL migration script yourself using the Microsoft SQL Server Management Studio.
See the next topic for more information.