Thank you very much.
I've found a way to solve it in logstash.
The elasticsearch-template.json in logstash is to describe the default template of mappings.
It's in the path:
${logstash_home}/vendor/bundle/jruby/1.9/gems/logstash-output-elasticsearch-2.5.1-java/lib/logstash/outputs/elasticsearch/elasticsearch-template.json
So I change the ignore_above attribute, then the long string in new index will be indexable.
Also , I need to add 'template_overwrite => true' to logstash.conf to make it into effect.
output {
elasticsearch {
hosts => ["https://esurl:443"]
ssl => true
flush_size => 250000
template_overwrite => true
}
}