Databases Reference
In-Depth Information
Read-Write Shards
In a read-write shard (RWS), all databases are considered read/write. In this case, you don't need to use a replication
topology that uses the SQL Data Sync Framework, because there is a single copy of each record within the shard.
Figure
2-9
shows an RWS topology.
Figure 2-9.
Multimaster shard topology
Although an RWS removes the complexity of synchronizing data between databases, the consumer is responsible
for directing all CRUD operations to the appropriate cloud database. This requires special considerations and
advanced development techniques to accomplish, as previously discussed, unless you use SQL Database Federations.
Offloading
In the offloading pattern, the primary consumer represents an existing onsite application with its own database;
but a subset of its data (or the entire database) is replicated to a cloud database using SQL Data Sync (or another
mechanism). The offloaded data can then be used by secondary consumers even if the primary database isn't
accessible.
You can implement the offloading pattern in two ways, as shown in Figure
2-10
. The primary database can be
either the local SQL Server database or the cloud database. For example, a legacy application can use a local SQL
Server database for its core needs. SQL Data Sync is then used to copy relevant or summary data in a cloud database.
Finally, secondary consumers such as portable devices and PDAs can display live summary data by connecting to
the cloud for their data source. Note that if you use the SQL Data Sync service, you can choose to have bidirectional
synchronization of data.
