处理多个Mysql数据库连接失败

Question

I'm Stuck at the situation where more than 1 Database connection needs to be handle. For example :

function update_user()
{
 #Establish connection with DB1
 #Update the user

 # Close connection with DB1
 #Establish connection with DB2
 #Update the user

 # Close connection with DB2
 #Establish connection with DB3
 #Update the user

}

In the above Algorithm I have to establish connection one by one and update the user from the corresponding tables.

My Question is : What happened when any of the DB connection failed and how can i roll back for the above executions ? For Example if DB1 Connection executes successfully and DB2 connection failed than what is the best way to roll back the execution of DB1.

My Proposed Solution : I think i can use the PHP to handle this, i just need to maintain the Array with updated records and ids. and Execute the Update query again for DB1 connection. But this case also fails when that time the DB1 Connection also got failed. So i can't handle it with PHP. what could be the solution ?

Answer 1

I would suggest using transactions within MySQL.

I would suggest starting a transaction after opening each connection (for each connection) and committing them when all the updates have succeeded or rolling them all back when they fail. This will ensure no rows are updated unless all of the updates succeed.

For more information on transactions, see here: https://dev.mysql.com/doc/refman/5.0/en/commit.html

Pseudo Code:

# Try
    # Establish connection with DB1
    # Create a transaction for DB1 connection 
    # Update the user

    # Establish connection with DB2
    # Create a transaction for DB2 connection
    # Update the user

    # Establish connection with DB3
    # Create a transaction for DB3 connection
    # Update the user

    # Commit all transactions
# Catch
    # Rollback all transactions, rethrow exception
# Finally
    # Close all connections