History-data staging and loading processes

There are separate processes for history-data staging and loading.

History data is collected continually in a staging area. It is loaded from the staging area into the history database at intervals determined by settings of the active history configuration.
History-data staging
After you enable history-data collection, the Netezza Performance Server system starts the history-data collection process (alcapp). This process captures history-data and saves it in a staging area, which is in the $NZ_DATA/hist/staging directory. This directory can have one or more subdirectories with names of the form alc_$TIMESEQUENCE. Each of these subdirectories contains:
  • One or more history-data files, each of which contains captured history data and is saved as an external table in text format
  • One CONFIG-INFO file that identifies which history configuration was active when the history-data files were created
History-data loading
The load settings specified in the history configuration determine when the history-data files in the staging area are transferred to the loading area. From the loading area, the history-data loader process (alcloader) loads the external tables into the history database. The current history configuration specifies the loading frequency, the target history database, and the user account to access that database.

The loading area is in the $NZ_DATA/hist/loading directory. This directory can have one or more subdirectories with names of the form alc_$TIMESEQUENCE. Each of these subdirectories contains the history-data files that are to be loaded.

After the history-data files are successfully loaded, the system deletes them to free disk space.

Error handling
An error might occur that prevents history-data files from being loaded. For example:
  • Someone might deactivate and drop the active history configuration before the corresponding history-data files are loaded.
  • The user password specified in the history configuration and used to access the history database might have changed.
  • The history database might be dropped or locked.
If the history-data files cannot be loaded, the loader moves the history-data files to the $NZ_DATA/hist/error directory. The nzvacuumcat process checks the files in the error directory and deletes any files that are older than 72 hours. To retry to load any files that were moved to the error directory:
  1. Resolve the problem that caused the load attempt to fail.
  2. Move the directories in $NZ_DATA/hist/error to $NZ_DATA/hist/loading.
  3. Issue the nzstop and nzstart commands to stop and restart the system.