Oniguruma Regx Parsing multiline logs

Elastic Stack Logstash
1

I am trying to parse multi-line logs in oniguruma regx and I understand logstash has a mutline filter but which way is better? To parse the logs with regx before logstash(or at?) or use the multi-line filter in the configuration file?

2

To parse the logs with regx before logstash(or at?)

Please explain what you mean by this.