[GitHub] [iotdb] jixuan1989 commented on pull request #1725: [IOTDB-23] Restart state monitor module

[GitBox <gi...@apache.org>]

jixuan1989 commented on pull request #1725:
URL: https://github.com/apache/iotdb/pull/1725#issuecomment-732752453


   ### Data Monitoring
   
   This module is for providing some statistics info about the writing operations: 
   
   * the data size (in bytes) in IoTDB, the number of data points in IoTDB;
   *  how many operations are successful or failed executed.
   
   #### Enable/disable the module
   
   Users can choose to enable or disable the feature of data statistics monitoring (set the `enable_stat_monitor` item in the configuration file).
   
   #### Statistics Data Storing
   
   By default, the statistics data is only saved in memory and can be accessed using Jconsole. 
   
   The data can also be written as some time series on disk. To enable it, set `enable_monitor_series_write=true`  in the configuration file. If so, using `select` statement in IoTDB-cli can query these time series.
   
   > Note: 
   > if `enable_monitor_series_write=true`, when IoTDB is restarted, the previous statistics data will be recovered into memory.
   >  if `enable_monitor_series_write=false`, IoTDB will forget all statistics data after the instance is restarted.
   
   #### Writing Data Monitor
   
   At present, the monitor system can be divided into two modules: `global writing statistics` and `storage group writing statistics`. The `global statistics` records the number of total points and requests, and the `storage group statistics` counts the write data of each storage group.
   
   The system sets the collection granularity of the monitoring module to **update the statistical information once one data file is flushed into the disk**, so the data accuracy may be different from the actual situation. To obtain accurate information, **Please call the `flush` method before querying**. 
   


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