What is the best DBMS to use together with my doctrine2 application
I have written a web application using doctrine2 with no sql only dql queries. 
I tested and developed it with mysql but my client thinks, that he needs sequence id generation. 

An other requirement to our dbms is referenceial integrity and that the dbms is fast. 

The web application has many actions which lead to update or create queries too, it is not only reading from the DB.

**What is the best recommendable DBMS for my needs?**
**Does it lead to problems when changing the underlying DBMS with doctrine or does this go easy?**

Because the project will be launched in some weeks there is no user data at the moment which must be migrated.
What is the best DBMS to use together with my doctrine2 application
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I have written a web application using doctrine2 with no sql only dql queries. 
I tested and developed it with mysql but my client thinks, that he needs sequence id generation. 

An other requirement to our dbms is referenceial integrity and that the dbms is fast. 

The web application has many actions which lead to update or create queries too, it is not only reading from the DB.

**What is the best recommendable DBMS for my needs?**
**Does it lead to problems when changing the underlying DBMS with doctrine or does this go easy?**

Because the project will be launched in some weeks there is no user data at the moment which must be migrated.