Property size is the number of bytes required to store the value of the property. Properties have either a fixed size or a variable size. If you add a fixed-size property to a catalog, Indexing Service sets the correct size for the property. You cannot change the size.
For variable-size properties, you can select the size. The entire value of each selected property is stored for each document, even if it is greater than the size you set. The size you set affects the amount of disk space required for the catalog and the amount of time it takes to process a query.
There are two considerations to keep in mind:
When setting the size for a variable-size property, make the best estimate you can of the size of the property for most documents, taking into account that the property may be empty for some documents, and then set the property size slightly larger. That should ensure that most values for the property will fit in the allotted space.
You can change the property size to improve performance or disk utilization. However, each time you make a change, you must do a full scan for the change to take effect for all documents.
For information on how to set the property size, see To add a property to the property cache
For information on doing a full scan, see To manually start a scan