README.md in fluent-plugin-cat-sweep-0.1.3 vs README.md in fluent-plugin-cat-sweep-0.1.4

@@ -35,10 +35,80 @@
 
 This plugin watches the directory (`file_path_with_glob tmp/test/access.log.*`), and reads the contents and sweep (deafault: remove) for files whose mtime are passed in 60 seconds (can be configured with `waiting_seconds`).
 
 Our assumption is that this mechanism should provide more durability than `in_tail` (batch read overcomes than streaming read). 
 
+## Potential problem of in_tail
+
+Assume that an application outputs logs into `/tmp/test/access.log` and rotates it in every one minute interval as
+
+(initial state)
+
+```
+tmp/test
+└── accesss.log (i-node 4478316)
+```
+
+(one minute later)
+
+```
+tmp/test
+├── accesss.log (i-node 4478319)
+└── accesss.log.1 (i-node 4478316)
+```
+
+(two minutes later)
+
+```
+tmp/test
+├── accesss.log (i-node 4478322)
+├── accesss.log.1 (i-node 4478319)
+└── accesss.log.2 (i-node 4478316)
+```
+
+Your configuration of `in_tail` may become as followings:
+
+```apache
+<source>
+  @type tail
+  path tmp/test/access.log
+  pos_file /var/log/td-agent/access.log.pos
+  tag access
+  format none
+</source>
+```
+
+Now, imagine that the fluentd process dies (or manually stops for maintenance) just before the 2nd file of i-node 4478319 is generated, and you restart the fluentd process after two minutes passed. Then, you miss the 2nd file of i-node 4478319.
+
+(initial state)
+
+```
+tmp/test
+└── accesss.log (i-node 4478316) <= catch
+```
+
+(fluentd dies)
+
+(one minute later)
+
+```
+tmp/test
+├── accesss.log (i-node 4478319) <= miss
+└── accesss.log.1 (i-node 4478316)
+```
+
+(two minutes later)
+
+(fluentd restarts)
+
+```
+tmp/test
+├── accesss.log (i-node 4478322) <= catch
+├── accesss.log.1 (i-node 4478319) <= miss
+└── accesss.log.2 (i-node 4478316)
+```
+
 ## Configuration
 
 ```
 <source>
   type cat_sweep
@@ -49,35 +119,35 @@
   # Input pattern. It depends on Parser plugin
   format tsv
   keys xpath,access_time,label,payload
 
   # Required. process files that are older than this parameter(seconds).
-  # [WARNING!!]: this plugin move or remove files even if the files open,
-  # so this parameter is set as seconds that the application close files definitely.  
+  # [WARNING!!]: this plugin moves or removes files even if the files are still open.
+  # make sure to set this parameter for seconds that the application closes files definitely.
   waiting_seconds 60
 
   # Optional. default is file.cat_sweep
   tag test.input
 
-  # Optional. processing files is renamed with this suffix. default is .processing
+  # Optional. processing files are renamed with this suffix. default is .processing
   processing_file_suffix .processing
 
-  # Optional. error files is renamed with this suffix. default is .error
+  # Optional. error files are renamed with this suffix. default is .error
   error_file_suffix .err
 
   # Optional. line terminater. default is "\n"
   line_terminated_by ,
 
-  # Optional. max bytes oneline can has. default 536870912 (512MB)
+  # Optional. max bytes oneline can have. default 536870912 (512MB)
   oneline_max_bytes 128000
 
-  # Optional. processed files are move to this directory.
+  # Optional. processed files are moved to this directory.
   # default '/tmp'
   move_to /tmp/test_processed
 
-  # Optional. this parameter indicated, `move_to` is ignored.
-  # files that is processed are removed.
+  # Optional. if this parameter is specified, `move_to` option is ignored.
+  # processed files are removed instead of being moved to `move_to` directory.
   # default is false.
   remove_after_processing true
 
   # Optional. default 5 seconds.
   run_interval 10
@@ -95,10 +165,9 @@
 
 ## Warning
 
 * This plugin supports fluentd from v0.10.45
 * The support for fluentd v0.10 will end near future
-* The support for fluentd v0.14 is not yet
 
 ## Contributing
 
 1. Fork it ( https://github.com/civitaspo/fluent-plugin-cat-sweep/fork )
 2. Create your feature branch (`git checkout -b my-new-feature`)