doc

doc/README.md

@@ -7,3 +7,22 @@ Rabit Documentation
 
 Parameters
 ====
+This section list all the parameters that can be passed to rabit::Init function as argv.
+All the parameters are passed in as string in format of ```parameter-name=parameter-value```.
+In most setting these parameters have default value or will be automatically detected,
+and do not need to be manually configured.
+
+* rabit_tracker_uri [passed in automatically by tracker] 
+  - The uri/ip of rabit tracker
+* rabit_tracker_port [passed in automatically by tracker]
+  - The port of rabit tracker
+* rabit_task_id [automatically detected]
+  - The unique identifier of computing process
+  - When running on hadoop, this is automatically extracted from enviroment variable
+* rabit_reduce_buffer [default = 256MB]
+  - The memory buffer used to store intermediate result of reduction
+  - Format "digits + unit", can be 128M, 1G
+* rabit_global_replica [default = 5]
+  - Number of replication copies of result kept for each Allreduce/Broadcast call
+* rabit_local_replica [default = 2]
+  - Number of replication of local model in check point