What are phantom reads?
PHANTOM READS: Data getting changed
in current transaction by other transactions is called Phantom Reads. New rows
can be added by other transactions, so you get different number of rows by
firing same query in current transaction.
What is Multisubnet Failover in ALWAYSON ?
If you are using client libraries
that support the MultiSubnetFailover connection option in the connection
string, you can optimize availability group failover to a different subnet by
setting MultiSubnetFailover to “True” or "Yes", depending on the
syntax of the provider you are using.
The MultiSubnetFailover connection
option only works with the TCP network protocol and is only supported when
connecting to an availability group listener and for any virtual network name
connecting to SQL Server 2017.
An example of the ADO.NET provider
(System.Data.SqlClient) connection string that enables multi-subnet failover is
as follows:
Server=tcp:AGListener,1433;Database=AdventureWorks;IntegratedSecurity=SSPI;
MultiSubnetFailover=True
The MultiSubnetFailover connection
option should be set to True even if the availability group only spans a single
subnet. This allows you to preconfigure new clients to support future spanning
of subnets without any need for future client connection string changes and
also optimizes failover performance for single subnet failovers. While the
MultiSubnetFailover connection option is not required, it does provide the
benefit of a faster subnet failover. This is because the client driver will
attempt to open up a TCP socket for each IP address in parallel associated with
the availability group. The client driver will wait for the first IP to respond
with success and once it does, will then use it for the connection.
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