2012-03-29 10:59:15 +0900: failed to flush the buffer, retrying. error="String not valid UTF-8" instance=5927920
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/bson-1.6.1/lib/bson/bson_c.rb:24:in `serialize'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/bson-1.6.1/lib/bson/bson_c.rb:24:in `serialize'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/mongo-1.6.1/lib/mongo/collection.rb:972:in `block in insert_documents'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/mongo-1.6.1/lib/mongo/collection.rb:971:in `each'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/mongo-1.6.1/lib/mongo/collection.rb:971:in `insert_documents'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/mongo-1.6.1/lib/mongo/collection.rb:353:in `insert'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluent-plugin-mongo-0.6.6/lib/fluent/plugin/out_mongo.rb:134:in `operate_inv
alid_records'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluent-plugin-mongo-0.6.6/lib/fluent/plugin/out_mongo.rb:113:in `operate'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluent-plugin-mongo-0.6.6/lib/fluent/plugin/out_mongo.rb:101:in `write'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.10/lib/fluent/buffer.rb:262:in `write_chunk'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.10/lib/fluent/buffer.rb:246:in `pop'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.10/lib/fluent/output.rb:299:in `try_flush'
  2012-03-29 10:59:15 +0900: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.10/lib/fluent/output.rb:121:in `run'