Default query row limit is 250 in most of Service-Now instances except Dublin which has 10000 default query row limit for JSON service. It is controlled by
a system property[of sys_properties table]:
To check ths property in table - Type sys_properties.list in the Navigation filter. The entire list of properties in the sys_properties table appears.When the property is not present, it uses the default value. If you want a different value, you'll have to create the property and if it is already existing then update its value. Please be aware that the Type of the variable must match what is expected. To create a new property click on New button in System Properties List. Give the Name as glide.processor.json.row_limit ,Type as Integer , Value as you want(in number) and Save/Update it.