Why is date filter in Logstash used?

Elastic Stack Logstash
1

I am extracting fields from grok expression out of which one field is a timestamp field. Later I am using date filter and matching with timestamp field. But the problem is timestamp field is not consistent always. It may be 2017-11-13 12:53:22.123456 or it may be 2017-11-13 12:53:22.1234. What should I do in this case?

Also if I am not wrong, date flter is used to convert a field from string to date type?

Please suggest me..

2

You can list multiple date patterns in a single date filter.

3

Exact pattern would be 2017-11-13 21:30:48:48319. What changes is just the milli second part. It may be 6 digits, 4 digits. So can I just use following,

date {
                                match => ["timestamp", "ISO8601"]
                                target => "time"
                        }