logstash file input，大量文件的报错

logstash的日志：
IdentityMapCodec has reached 80% capacity {:current_size=>16427, :upper_limit=>20000, :level=>:warn}

系统的文件限制已经设置过了

$ ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 63474
max locked memory (kbytes, -l) 65535
max memory size (kbytes, -m) unlimited
open files (-n) 655350
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 4096
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited