Final answer:
In the Salesforce multitenant environment, it is not true that Salesforce delivers polyglot persistence, but it is possible to index data, and queries do need to be selective. Additionally, while custom domains improve security, data segregation is maintained largely through access controls.
Step-by-step explanation:
The question refers to the characteristics of developing applications within Salesforce's multitenant environment. Let's address each statement:
- Salesforce delivers polyglot persistence transparently: This is not entirely accurate. Salesforce uses a multitenant architecture where the same infrastructure and codebase serve multiple customers, but it primarily relies on its own database technologies, lightning platform, and Apex programming language, rather than supporting multiple types of database systems (which is what 'polyglot persistence' implies).
- It is possible to index application data, despite the system's multitenant nature. Salesforce offers ways to index fields and use indexing to speed up queries even though data from different tenants is stored together.
- Queries need to be selective regarding the number of records returned: This statement is true. Salesforce enforces query selectiveness to ensure that operations are efficient and limits are not exceeded, which could otherwise impact the performance of the shared resources.
- The custom domain feature does enhance security and help ensure that customers' data remains separate; however, it's Salesforce's rigorous data access controls and data storage architecture that primarily prevent users from accessing other tenants' data.