When talking about maximum length of EL events (because of URL length restriction) I remembered that Pivot/Turnilo uses base64 to encode json objects for the URL. The base64 event is actually larger in size than the raw json event (base64 increases in 4/3 the size of the original message). But EL is not sending the raw json, it sends the URI encoded version of it, which is (afaik) longer than the base64. See example (this event has been redacted):
The raw event: 1033 chars
{"dt": "2018-01-01T00:00:00Z", "event": {"action": "extClick", "dom_interactive_time": 1531275743841, "event_offset_time": 8946, "ext_position": 64, "freely_accessible": false, "in_infobox": false, "link_occurrence": 3, "link_text": "\"Some Text\"", "link_url": "https://some.host.org/path1/path2/path3", "mode": "desktop", "namespace_id": 0, "page_id": 16767922, "page_title": "Blah Blah Blah", "page_token": "kjhg395hg8745", "referrer": "https://www.google.com/", "revision_id": 845632768, "section_id": "Some_section", "session_token": "39hg4g8457h4545gh9", "skin": "vector"}, "ip": "11.111.11.11", "recvFrom": "cp5008.eqsin.wmnet", "revision": 13563478, "schema": "CitationUsage", "seqId": 6457542, "userAgent": {"browser_family": "Chrome", "browser_major": "100", "browser_minor": "100", "device_family": "Other", "is_bot": false, "is_mediawiki": false, "os_family": "Windows", "os_major": "10", "os_minor": null, "wmf_app_version": "-"}, "uuid": "4890tu394583498h4g9345yhguoi4", "webHost": "en.wikipedia.org", "wiki": "enwiki"}The current URI encoded event: 1641 chars
%7B%22dt%22%3A%20%222018-01-01T00%3A00%3A00Z%22%2C%20%22event%22%3A%20%7B%22action%22%3A%20%22extClick%22%2C%20%22dom_interactive_time%22%3A%201531275743841%2C%20%22event_offset_time%22%3A%208946%2C%20%22ext_position%22%3A%2064%2C%20%22freely_accessible%22%3A%20false%2C%20%22in_infobox%22%3A%20false%2C%20%22link_occurrence%22%3A%203%2C%20%22link_text%22%3A%20%22%22Some%20Text%22%22%2C%20%22link_url%22%3A%20%22https%3A%2F%2Fsome.host.org%2Fpath1%2Fpath2%2Fpath3%22%2C%20%22mode%22%3A%20%22desktop%22%2C%20%22namespace_id%22%3A%200%2C%20%22page_id%22%3A%2016767922%2C%20%22page_title%22%3A%20%22Blah%20Blah%20Blah%22%2C%20%22page_token%22%3A%20%22kjhg395hg8745%22%2C%20%22referrer%22%3A%20%22https%3A%2F%2Fwww.google.com%2F%22%2C%20%22revision_id%22%3A%20845632768%2C%20%22section_id%22%3A%20%22Some_section%22%2C%20%22session_token%22%3A%20%2239hg4g8457h4545gh9%22%2C%20%22skin%22%3A%20%22vector%22%7D%2C%20%22ip%22%3A%20%2211.111.11.11%22%2C%20%22recvFrom%22%3A%20%22cp5008.eqsin.wmnet%22%2C%20%22revision%22%3A%2013563478%2C%20%22schema%22%3A%20%22CitationUsage%22%2C%20%22seqId%22%3A%206457542%2C%20%22userAgent%22%3A%20%7B%22browser_family%22%3A%20%22Chrome%22%2C%20%22browser_major%22%3A%20%22100%22%2C%20%22browser_minor%22%3A%20%22100%22%2C%20%22device_family%22%3A%20%22Other%22%2C%20%22is_bot%22%3A%20false%2C%20%22is_mediawiki%22%3A%20false%2C%20%22os_family%22%3A%20%22Windows%22%2C%20%22os_major%22%3A%20%2210%22%2C%20%22os_minor%22%3A%20null%2C%20%22wmf_app_version%22%3A%20%22-%22%7D%2C%20%22uuid%22%3A%20%224890tu394583498h4g9345yhguoi4%22%2C%20%22webHost%22%3A%20%22en.wikipedia.org%22%2C%20%22wiki%22%3A%20%22enwiki%22%7D
The base64 event: 1376 chars
eyJkdCI6ICIyMDE4LTAxLTAxVDAwOjAwOjAwWiIsICJldmVudCI6IHsiYWN0aW9uIjogImV4dENsaWNrIiwgImRvbV9pbnRlcmFjdGl2ZV90aW1lIjogMTUzMTI3NTc0Mzg0MSwgImV2ZW50X29mZnNldF90aW1lIjogODk0NiwgImV4dF9wb3NpdGlvbiI6IDY0LCAiZnJlZWx5X2FjY2Vzc2libGUiOiBmYWxzZSwgImluX2luZm9ib3giOiBmYWxzZSwgImxpbmtfb2NjdXJyZW5jZSI6IDMsICJsaW5rX3RleHQiOiAiIlNvbWUgVGV4dCIiLCAibGlua191cmwiOiAiaHR0cHM6Ly9zb21lLmhvc3Qub3JnL3BhdGgxL3BhdGgyL3BhdGgzIiwgIm1vZGUiOiAiZGVza3RvcCIsICJuYW1lc3BhY2VfaWQiOiAwLCAicGFnZV9pZCI6IDE2NzY3OTIyLCAicGFnZV90aXRsZSI6ICJCbGFoIEJsYWggQmxhaCIsICJwYWdlX3Rva2VuIjogImtqaGczOTVoZzg3NDUiLCAicmVmZXJyZXIiOiAiaHR0cHM6Ly93d3cuZ29vZ2xlLmNvbS8iLCAicmV2aXNpb25faWQiOiA4NDU2MzI3NjgsICJzZWN0aW9uX2lkIjogIlNvbWVfc2VjdGlvbiIsICJzZXNzaW9uX3Rva2VuIjogIjM5aGc0Zzg0NTdoNDU0NWdoOSIsICJza2luIjogInZlY3RvciJ9LCAiaXAiOiAiMTEuMTExLjExLjExIiwgInJlY3ZGcm9tIjogImNwNTAwOC5lcXNpbi53bW5ldCIsICJyZXZpc2lvbiI6IDEzNTYzNDc4LCAic2NoZW1hIjogIkNpdGF0aW9uVXNhZ2UiLCAic2VxSWQiOiA2NDU3NTQyLCAidXNlckFnZW50IjogeyJicm93c2VyX2ZhbWlseSI6ICJDaHJvbWUiLCAiYnJvd3Nlcl9tYWpvciI6ICIxMDAiLCAiYnJvd3Nlcl9taW5vciI6ICIxMDAiLCAiZGV2aWNlX2ZhbWlseSI6ICJPdGhlciIsICJpc19ib3QiOiBmYWxzZSwgImlzX21lZGlhd2lraSI6IGZhbHNlLCAib3NfZmFtaWx5IjogIldpbmRvd3MiLCAib3NfbWFqb3IiOiAiMTAiLCAib3NfbWlub3IiOiBudWxsLCAid21mX2FwcF92ZXJzaW9uIjogIi0ifSwgInV1aWQiOiAiNDg5MHR1Mzk0NTgzNDk4aDRnOTM0NXloZ3VvaTQiLCAid2ViSG9zdCI6ICJlbi53aWtpcGVkaWEub3JnIiwgIndpa2kiOiAiZW53aWtpIn0=
So for this specific case the base64 event is around 20% shorter than the current URI encoded one. The gain is not huge though, and we lose readability which is an important factor when grep-ing logs, although probably there's a solution for that. So, should we look deeper into this?