In today’s business world, reporting applications play a crucial role in making informed decisions. Retail companies, for example, rely on reports to analyze customer traffic, sales amounts, revenue, and profits. To meet the ever-changing business needs, enhancements are often requested, such as adding new columns to existing tables or creating new tables in a SQL Server database.
However, implementing these enhancements can be challenging, especially when dealing with large tables containing billions of rows. The goal is to make these enhancements without causing any significant downtime for the reporting application. In this article, we will discuss a step-by-step process to load historical data into existing large tables without impacting the reporting application.
Implementation Process
The following steps outline the process of implementing enhancements without downtime:
- Create replica table structures (without data)
- Alter the newly created replica table structures with new columns
- Create any new tables needed for enhancement
- Insert data into replica tables
- Validate the data in new replica tables
- Rename/swap the tables
Create Replica Table Structures
To begin, create replica table structures without data. This can be done by using the “SELECT INTO” or “CREATE TABLE AS SELECT” commands. It is important to note that this approach does not carry over indexes, keys, constraints, and permissions. Therefore, it is not the preferred approach. Instead, using the DDL of the existing table is recommended.
Alter the Newly Created Replica Table Structures
Next, alter the newly created replica table structures by adding the new columns required for the enhancement. This can be done using the “ALTER TABLE” command.
Create New Tables Needed
If new tables are needed for the enhancement, create them accordingly. These tables can be populated with historical data using an ETL tool like SQL Server Integration Services (SSIS) or through manual INSERT statements.
Insert Data into Replica Tables
Once the replica tables and new tables are set up, load the data into the replica tables using SQL statements. If dealing with a large number of records, it may be necessary to split the insert statements into smaller chunks to avoid overwhelming the system.
Validate the Data in Replica Tables
After loading the data, it is important to validate its accuracy. Compare the count of records in the original table and the replica table to ensure they match. Additionally, compare the data in the existing columns between the original table and the replica table to ensure they are in sync.
Rename/Swap the Tables
Once the data in the replica tables has been validated, rename the original table to a different name (e.g., “invoice_old”) and rename the replica table to the original table name (e.g., “invoice”). This renaming process can be scheduled during a maintenance window to minimize any impact on the business.
Conclusion
Implementing enhancements to a SQL Server-based reporting application can be done without causing any downtime. By following the steps outlined in this article, businesses can add new columns or create new tables while ensuring the reporting application remains available for decision-making. It is important to validate the data and schedule the renaming of tables during a maintenance window to minimize any impact on the business.