Add_field parameter in filter plugins

Elastic Stack Logstash
1

Hi,
Can anyone explain what does add_field do ?

filter { mutate { add_field => { "COLUMN2" => "%{COLUMN1}" } } }
What is the difference between add_field present in mutate, clone, kv and grok plugins

2

Can anyone explain what does add_field do ?

It adds a field to the current event. I don't know how to explain that in any different way.

What is the difference between add_field present in mutate, clone, kv and grok plugins

With the exception of mutate, add_field and remove_field only apply if the filter was successful (where the meaning of success depends on the filter). In other words,

filter {
  grok {
    match => ["foo", "..."]
    remove_field => ["foo"]
  }
}

is a convenient way of parsing a field with grok and deleting the original field only if the grok match was successful.

4

adds a field means is that added as a new column in es index if output is an elasticsearch index

5

adds a field means is that added as a new column in es index if output is an elasticsearch index

Elasticsearch has no "column" concept, but yes.