Forum Discussion
Is the use of NVARCHAR(MAX) acceptable for this scenario?
- Acceptability of NVARCHAR(MAX):
Pros:
Flexibility: Accommodates changes in source field lengths without requiring table schema changes in the target database.
Resilience: Reduces the risk of ADF pipeline failures or data truncation issues due to schema changes in source tables.
Cons:
Performance: NVARCHAR(MAX) can potentially impact performance, especially if large amounts of data are stored.
Indexing: Indexing on NVARCHAR(MAX) columns is less efficient compared to fixed-length NVARCHAR columns.
Best Practices: Using NVARCHAR(MAX) for all columns is generally not recommended unless necessary.
Hybrid Approach:
Use NVARCHAR with a reasonable length for most columns based on the current source data length.
Reserve NVARCHAR(MAX) for columns where you expect significant changes in data length or where you cannot predict future length requirements.
Monitoring and Alerts:
Implement monitoring and alerting for schema changes in source tables. Tools like Azure Data Factory and Azure SQL Database provide monitoring capabilities that can help you track changes and respond proactively.
Regular Audits:
Periodically audit the source and target schemas to ensure they remain in sync. This can help you catch any changes early and adjust the target schema as needed.
sing NVARCHAR(MAX) can be acceptable in your scenario, especially for fields where length can vary or change unexpectedly. However, consider a balanced approach to avoid potential performance impacts and maintain best practices. The cost in Azure SQL Server will primarily depend on the actual data stored, not the maximum potential size of NVARCHAR(MAX) fields.
Pros:
Flexibility: Accommodates changes in source field lengths without requiring table schema changes in the target database.
Resilience: Reduces the risk of ADF pipeline failures or data truncation issues due to schema changes in source tables.
Cons:
Performance: NVARCHAR(MAX) can potentially impact performance, especially if large amounts of data are stored.
Indexing: Indexing on NVARCHAR(MAX) columns is less efficient compared to fixed-length NVARCHAR columns.
Best Practices: Using NVARCHAR(MAX) for all columns is generally not recommended unless necessary.
Hybrid Approach:
Use NVARCHAR with a reasonable length for most columns based on the current source data length.
Reserve NVARCHAR(MAX) for columns where you expect significant changes in data length or where you cannot predict future length requirements.
Monitoring and Alerts:
Implement monitoring and alerting for schema changes in source tables. Tools like Azure Data Factory and Azure SQL Database provide monitoring capabilities that can help you track changes and respond proactively.
Regular Audits:
Periodically audit the source and target schemas to ensure they remain in sync. This can help you catch any changes early and adjust the target schema as needed.
sing NVARCHAR(MAX) can be acceptable in your scenario, especially for fields where length can vary or change unexpectedly. However, consider a balanced approach to avoid potential performance impacts and maintain best practices. The cost in Azure SQL Server will primarily depend on the actual data stored, not the maximum potential size of NVARCHAR(MAX) fields.
bandaruajeyudu - thank you for your response.
My comments based on your feedback are:
1) By using NVARCHAR(MAX) I would avoid the need to amend the target structure should the source change. This is a benefit, and so is the truncation avoidance concern.
2) We won't be storing a large amount of data in our target database that I'm considering using NVARCHAR(MAX) in. There may be 50 tables and each table may be 30 columns wide and 30k rows deep.
3) I don't expect to explicitly create indexes on the target tables. Unless Azure SQL Server implicitly creates indexes on the tables then I feel the limitation of indexing when using NVARCHAR(MAX) concern is not relevant here.
4) The hybrid approach seems sensible. It would take a little more effort upfront but result in a more suitable approach. The concern here though is I have no idea if the source, maintained by external parties, would change and how. Using NVARCHAR(MAX) seems lazy but I wouldn't be using it for this reason, but instead to future-proof any source changes.
5) You mentioned Azure Data Factory has the ability to monitor source changes. This sounds very useful. Please can you provide me with a link to what you're describing? If this monitoring can alert me to a source field (or even just a table) change then this could be relied on and therefore I wouldn't need the failsafe approach of using NVARCHAR(MAX).
Thanks.
