Qlik Replicate's core functionality for near real-time data replication is Change Data Capture (CDC). The primary method for CDC involves non-intrusively reading the source database's native transaction logs (e.g., Redo Logs in Oracle, Transaction Log in SQL Server, Write-Ahead Log in PostgreSQL). This allows Replicate to capture INSERT, UPDATE, and DELETE operations as they occur without placing significant load on the source system. Therefore, providing Replicate with the necessary permissions and access path to these logs is a fundamental prerequisite for configuring most transactional database source endpoints, in addition to standard connectivity credentials.

A. Database client: This is a component required to establish the connection itself and is implicitly part of setting up a valid "connection string".

B. File access: This is too generic. While some log access methods might require direct file system permissions, the essential requirement is access to the log data, which can be achieved via various database-specific APIs or functions.

D. Access to database server: This is a basic prerequisite for using a connection string and credentials to connect to the database; it is not a distinct, additional element.

1. Qlik Replicate Documentation - Setting up Oracle as a source: The official documentation states, "To enable Qlik Replicate to capture changes, the user specified in the Oracle endpoint settings must be granted the required privileges." It then lists specific privileges required for "Access to the online and archived redo logs," which are Oracle's transactional logs.

Source: Qlik Help Portal, Qlik Replicate Documentation, "Prerequisites for using Oracle as a source," Section: "Required permissions."

2. Qlik Replicate Documentation - Setting up Microsoft SQL Server as a source: The documentation specifies permissions needed for different log access methods. For the Transaction Log Access method, it states, "The following permissions are required when accessing the transaction logs..." and lists permissions such as VIEW SERVER STATE and dbowner. This directly links endpoint setup to transactional log access.

Source: Qlik Help Portal, Qlik Replicate Documentation, "Prerequisites for using Microsoft SQL Server as a source," Section: "Required permissions for accessing the transaction logs."

3. Qlik Replicate Documentation - Change Data Capture Concepts: The general product documentation explains the underlying mechanism: "During CDC, Qlik Replicate reads the database transaction logs... When Qlik Replicate is started, it reads the transaction log from the time of the last successfully processed transaction..." This establishes that log reading is central to the product's operation.

Source: Qlik Help Portal, Qlik Replicate Documentation, "Using Change Data Capture (CDC)," Section: "How does CDC work?"