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DS_HDB

Process Template used to query at high speed the persisted historical database directory structure. The HDB loads the historical data base from the HDB directory. Data is typically written to the HDB directory during EOD events in the associated RDB. The data is usually saved as a table splayed by date and grouped by sym.

Parameters

The below table details the HDB template parameters.

name type default value description
directory Symbol Base directory HDB is located
gatewayQuery Analytic dxQuery_Basic Specifies which analytic to use to handle gateway queries
initialStateFunct Analytic dxEmptyFunction Specifies initial state tasks, executed after loading base directory
messagingServer Configuration DS_MESSAGING_SERVER Messaging server
subscriptionChannel Symbol Channel to subscribe to
subscriptionTableList Symbol[] List of tables to subscribe to
publishChannel Symbol Channel to publish on
publishTableList Symbol[] List of tables to publish to
realTimeMsgFunct Analytic dxEmptyFunction Real-time messaging function
reloadFunct Analytic dxEmptyFunctionNull Function called when HDB is reloaded

Initialisation

  • The HDB directory is loaded by the .ds.hdb.loadDbDir function.
  • The initialStateFunct assigned in the input parameters is executed. Common actions executed at this stage include the loading of pip maps or corporate action variables.

End-Of-Day

  • During an EOD, the RDB saves down data to the relevant directory as dictated by the hdb configuration. The RDB has a parameter that allows the user to specify the corresponding HDB process instance that it should be paired with. The RDB will use the ‘Directory’ parameter of this process instance to determine where to write the data by default.
  • In the default EOD function the .ds.hdb.reloadDB function is called in the HDB process which reloads the updated historical database without calling the initialStateFunct.

APIs

.ds.hdb.reloadDB

Reloads historical database and calls reload analytic.

Example:

.ds.hdb.reloadDB[];

<->2020.07.06D14:58:27.655 ### normal ### (22864): Reloading database ### `/install/delta-data/DeltaStreamData/opshdblog
<->2020.07.06D14:58:27.660 ### normal ### (22864): Reloaded database ### `/install/delta-data/DeltaStreamData/opshdblog
<->2020.07.06D14:58:27.660 ### normal ### (22864): Running HDB reload analytic ### 

.ds.hdb.reloadDBOnly

Reloads historical database without calling reload analytic.

Example:

.ds.hdb.reloadDBOnly[];

<->2020.07.06D14:58:27.655 ### normal ### (22864): Reloading database ### `/install/delta-data/DeltaStreamData/opshdblog
<->2020.07.06D14:58:27.660 ### normal ### (22864): Reloaded database ### `/install/delta-data/DeltaStreamData/opshdblog