Saving XML in SPListItem

Question

I have written a custom comment box control which saves the data in a XML format into the relevant field of a SPListItem. Is there a limitation to what amount of data can be stored in a field and will it at some point cause severe performance issues?

File size (XML Serialization) - Optimal File Size

• 500 Comments - 322KB
• 1000 Comments - 643KB
• 5000 Comments - 3212KB

File size (Binary Serialization) - Optimal Performance

• 500 Comments - 378KB
• 1000 Comments - 752KB
• 5000 Comments - 3751KB

Unfortunately I can't save the data in a separate database as it is essential to keep all the data intact as it will be declared as a record once it reaches it's retention policy.

Answer 1

With these size estimates you don't really have anything to worry about. Multiple lines of text fields are stored as NTEXT Sql type columns. This type of columns can store up to 2GB of data. Obviously, it's not advisable to store such a huge amount of data in a single field, but you are way below this limit.