Partitioning a Database

Partitioning means breaking up a database into sections - to make it more performant, easier to manage or for load balancing.

Partitioning Criteria (Key-Partition Pairs)

RDBMS's support a range of partitioning criteria. 

They take a partitioning key and assign a partition based on certain criteria. 

Example criteria are:

• Hash partitioning - membership of a partition is determined by the value of a hash function. This function might return numbers between 0 to 4, for example, if there are 5 partitions.
• Range partitioning - selects partition if partitioning key lies within a given range. For example, if you have a list of countries, you may split on a country with the letter M, say Malawi, Malta or the Maldives.
• List partitioning - the partition is assigned a list of values. If the row satisfies the criteria (e.g. Country column is contained in List A) then it goes into, say, partition A.
• Composite partitioning - hybrid of the above approaches.

Means of Partitioning

"Horizontal partitioning" or "horizontal sharding" involves putting different rows into different tables. A view with a union may be used to create a unified view.

"Vertical partitioning" involves taking normalisation to the next level. It involves creating tables with fewer columns and using additional tables to store the extra columns - a bit like normalisation, except vertical partitioning can be effected even when the tables are normalised. Infrequently used columns might be stored on a different device. This type of partitioning is also known as "row splitting" - the row is split by the columns.

AppDomains in .NET and why Threads are Special

AppDomains in .NET and Their Relationship to Processes, Assemblies and Threads

An Application Domain , or AppDomain, in .NET, provides a boundary wall between running .NET applications, to enhance reliability and security. They are like discrete pinball machines.

AppDomains and Processes; Plus Points of Partitioning Arrangement

AppDomains are structured such that several of these domains may be run in a single process; in math terms, the process space is partitioned into AppDomain space i.e. can have several of these non-intersecting AppDomains that make up the process space. This avoids the "resident" applications from the overhead of making inter-process calls when they need to communicate (everyone is in the same process "locale").

AppDomains and Assemblies

A .NET assembly must be loaded into an AppDomain in order to be able to run. A typical application will load several assemblies into a single AppDomain.

AppDomains and Threads

A thread must run in an AppDomain, but has the ability to cross into other AppDomains. They are bit like electrons within atoms.(Thread.GetDomain will tell you what AppDomain a thread is currently running in).