README.md in fluent-plugin-groupcounter-0.1.0 vs README.md in fluent-plugin-groupcounter-0.2.0

@@ -1,43 +1,124 @@
 # fluent-plugin-groupcounter
 
-## Component
+Fluentd plugin to count like SELECT COUNT(\*) GROUP BY.
 
-### GroupCounterOutput
-
-Fluentd plugin to count like COUNT(\*) GROUP BY
-
 ## Configuration
 
-## GroupCounterOutput
+Assume inputs are coming as followings:
 
-    <source>
-      type tail
-      path /var/log/httpd-access.log
-      tag apache.access
-      format apache
-    </source>
+    apache.access: {"code":"200", "method":"GET", "path":"/index.html", "reqtime":"1.001" }
+    apache.access: {"code":"404", "method":"GET", "path":"/foo.html",   "reqtime":"2.002" }
+    apache.access: {"code":"200", "method":"GET", "path":"/index.html", "reqtime":"3.003" }
 
+Think of quering `SELECT COUNT(\*) GROUP BY code,method,path`. Configuration becomes as below:
+
     <match apache.access>
       type groupcounter
-      count_interval 5s
       aggregate tag
       output_per_tag true
       tag_prefix groupcounter
       group_by_keys code,method,path
     </match>
 
-Output like below
+Output becomes like
 
-    groupcounter.apache.access: {"200_GET_/index.html_count":1,"200_GET_/index.html_rate":0.2,"200_GET_/index.html_percentage":100.0}
+    groupcounter.apache.access: {"200_GET_/index.html_count":2, "404_GET_/foo.html_count":1}
 
-## TODO
+## Parameters
 
-* tests
-* documents
+* group\_by\_keys (semi-required)
 
+    Specify keys in the event record for grouping. `group_by_keys` or `group_by_expression` is required.
+
+* delimiter
+
+    Specify the delimiter to join `group_by_keys`. Default is '_'.
+
+* group\_by\_expression (semi-required)
+
+    Use an expression to group the event record. `group_by_keys` or `group_by_expression` is required.
+
+    For examples, for the exampled input above, the configuration as below
+
+        group_by_expression ${method}${path}/${code}
+
+    gives you an output like
+
+        groupcounter.apache.access: {"GET/index.html/200_count":1, "GET/foo.html/400_count":1}
+
+    SECRET TRICK: You can write a ruby code in the ${} placeholder like
+
+        group_by_expression ${method}${path.split(".")[0]}/${code[0]}xx
+
+    This gives an output like
+
+        groupcounter.apache.access: {"GET/index/2xx_count":1, "GET/foo/4xx_count":1}
+
+* tag
+
+    The output tag. Default is `groupcount`.
+
+* tag\_prefix
+
+    The prefix string which will be added to the input tag. `output_per_tag yes` must be specified together. 
+
+* input\_tag\_remove\_prefix
+
+    The prefix string which will be removed from the input tag.
+
+* count\_interval
+
+    The interval time to count in seconds. Default is `60`.
+
+* unit
+
+    The interval time to monitor specified an unit (either of `minute`, `hour`, or `day`).
+    Use either of `count_interval` or `unit`.
+
+* store\_file
+
+    Store internal data into a file of the given path on shutdown, and load on starting.
+
+* max\_key
+
+    Specify key name in the event record to do `SELECT COUNT(\*),MAX(key_name) GROUP BY`.
+
+    For examples, for the exampled input above, adding the configuration as below
+
+        max_key reqtime
+
+    gives you an output like
+
+        groupcounter.apache.access: {"200_GET_/index.html_reqtime_max":3.003, "404_GET_/foo.html_reqtime_max":2.002}
+
+* min\_key
+
+    Specify key name in the event record to do `SELECT COUNT(\*),MIN(key_name) GROUP BY`.
+
+* avg\_key
+
+    Specify key name in the event record to do `SELECT COUNT(\*),AVG(key_name) GROUP BY`.
+
+* count\_suffix
+
+    Default is `_count`
+
+* max\_suffix
+
+    Default is `_max`. Should be used with `max_key` option.
+
+* min\_suffix
+
+    Default is `_min`. Should be used with `min_key` option.
+
+* avg\_suffix
+
+    Default is `_avg`. Should be used with `avg_key` option.
+
 ## Copyright
 
 * Copyright
   * Copyright (c) 2012- Ryosuke IWANAGA (riywo)
+  * Copyright (c) 2013- Naotoshi SEO (sonots)
 * License
   * Apache License, Version 2.0