Insert:

• Partial insert is not supported.
• Roll back is not supported.
• If we use the DML statement (Insert) in bulk operation, then if error occurs the execution will stop. In that case Apex code throws an error and none of the record will insert to the database.

Database.Insert

• Database methods are static methods available in Database class.
• Partial insert is supported.
• Roll back is supported.
• Includes the optional allorNone parameters that defaults true.
• If we use DML database methods (Database.Insert) in bulk operation, then if error occurs the remaining records will be inserted/updated means partial DML operation will be done. The only record throwing an error will not be inserted/updated.

Example: If we are inserting 10 records in an object, Where 5 records are correct and remaining 5 records are incorrect.

• In DML statement (Insert) all the 10 records will be failed, because if one record is incorrect or error means all other remaining records will not be inserted. It will throw error.
• In Database.insert 5 records will be inserted, remaining 5 records will be failed.(i.e. Partial DML Operation).

An exception is a special condition that changes the normal flow of program execution. That is, it’s when something bad happens that the program can’t deal with during execution. Exceptions are the language’s way of throwing up its hands and saying, I can’t deal with this, you need to handle those exceptions. we have three methods to catch this exceptions.

Apex allows to handle your exceptions, and write code to gracefully recover from an error. Apex uses the Try, Catch, Finally construct common to many other programming languages.

Try: If an exception occurs within the try block, that exception is handled by an exception handler associated with it. To associate an exception handler with a try block, you must put a catch block after it.
Catch: Each catch block is an exception handler that handles the type of exception indicated by its argument. The argument type, ExceptionType , declares the type of exception that the handler can handle and must be the name of a class that inherits from the Throwable class. The handler can refer to the exception with name.
Finally: This ensures that the finally block is executed even if an unexpected exception occurs. But finally is useful for more than just exception handling it allows the programmer to avoid having cleanup code accidentally bypassed by a return , continue , or break.

Simply You “try” to run your code. If there is an exception, you “catch” it and can run some code, then you can “finally” run some code whether you had an exception or not.

Here is an example of what these statements look like and the order in which they should be written:

try {
    // Perform some database operations that 
    //   might cause an exception.
} catch(DmlException e) {
    // DmlException handling code here.
} catch(Exception e) {
    // Generic exception handling code here.
} finally {
    // Perform some clean up.
}

Salesforce.com introduced Custom Settings in Winter ’10 which allows you to store custom data sets and associate them on an org-wide, profile or user basis. Custom settings data is exposed in the application cache and do not count against SOQL limits when fetched. This data can then be used by formula fields, validation rules, Apex, and the SOAP API.

Custom Settings support only Checkbox, Currency, Date, Date/Time, Email, Number, Percent, Phone, Text, Text Area, and URL field types. You can’t create Formula and Picklist, as well as field types that define relationships to other objects, like Lookup and Master/Detail. You can’t create lookups from Custom Objects to Custom Settings either. No Page layouts, record types, validation rules, triggers and workflow rules can be used on Custom Settings.

There are two types of custom settings:

List Custom Settings: It provides a reusable set of static data that can be accessed across your organization. If you use a particular set of data frequently within your application, putting that data in a list custom setting streamlines access to it. Data in list settings does not vary with profile or user, but is available organization-wide.

Hierarchy Custom Settings: Hierarchical Custom Settings are defined once and can hold a unique set of values for the Organization, each Profile or each individual User. Salesforce automatically grabs the lowest level of setting for the running user when a getInstance() call is made, or when accessed in a configuration such as a Validation Rule, Workflow or Formula Field. Only Hierarchical settings can be accessed declaratively whereas List settings are for Apex/Visualforce only.

Limitation of Custom Setting:

• Maximum total data of 10 MB, but if you have less than 10 license users, multiply 1 MB with number of users.
• 300 fields per custom setting..
• Can’t share a custom setting record.
• No owner assigned for each custom setting record.
• Each custom setting counts against the total number of custom objects available for your organization.

Note: If you include custom settings in your distributed package you’ll need to build in some scripts which populate the settings with data after the package has been installed.