I do:
grok { match => { "message" => "%{GREEDYDATA:foo}" } }
and I would expect that message and foo are the same, but foo is only the first ~4000 chars of message. I don't believe this is an event size issue, as I'm testing it with stdin/sdtout, and message is correctly shown as about 6000 chars. But foo has only the first 4000.
Alex