ignore_above of 1024 for
agent.name means that if a document contains a field
agent.name with a value that is bigger than 1024 characters, this field will ignored and will not be indexed, as though this document doesn't have a field
agent.name (the source will still be saved in the original format).
If all values of your
agent.name have less than 10 characters, changing
ignore_above for anything less than 10 characters will have no effect. If you change it to 9 characters, fields that have values bigger than 9 will be ignored, not indexed and you will save space there at the expense that you will not be able search by
agent.name for these documents.