Historic Database (HDB) Files and Configuration Options
Canary writes a separate Historic Database (HDB) File for each Dataset. By default, the files are saved in C:\HistorianData and are organized within each Dataset folder. These HDB files can Roll-Over, Roll-Up, and be Deleted. Roll-Over and Roll-Up work together to reduce the risk of file corruption and data loss, while conserving as much storage space as possible.
HDB files are intended to Roll-Over each day, providing a single HDB file per DataSet per day. If the file grows to large, it will automatically Roll-Over at 512 MB. It is best to limit tag load to ensure HDB files are not reaching the 512 MB capacity. Typically this can be accomplished by logging less than 25,000 tags to a DataSet but may need reduced based on poll rate and rate-of-change of your data.
HDB files have several benefits. These include a built-in mechanism to automatically validate and then compress the file upon Roll-Over.
Validate
This configurable feature enables the Canary System to automatically validate HDB files, checking them for errors prior to compression. When the 'Validate' checkbox is selected, a background process validates all HDB files for the DataSet after a Roll-Over has occurred, typically once per day.
Email Notification
The 'Email if no data received in' checkbox configures the Historian to send an email notification.
The notification alerts the system administrator of a lack of data received within the user specified time-frame. Learn how to configure the Canary System to send emails in this article.
Roll-Over
The Roll-Over setting determines when the current HDB file closes and a new one is created. The only time an HDB file is susceptible to corruption is when it is opened for writing. A power outage or an uncontrolled shutdown could corrupt an open HDB file, making it unusable. Therefore, maintaining no more than a single HDB file per day helps minimize risk. A single HDB file per day is also ideal for faster data retrieval speeds.
Roll-Up
The Roll-up setting determines how often HDB2 files get condensed into one 'rolled-up' file. A 'rolled-up' file is either daily, weekly, monthly, or quarterly depending on how many HDB2 files the system administrator wishes to condense. Files are condensed to save storage space. Condensed files save storage space by deleting tag and metadata property descriptions for an HDB file's TVQs. For example, instead of listing Tag0001 in thirty separate HDB2 files, a 'Roll-up' lists Tag0001 in one monthly file while retaining all of Tag0001's TVQs from the last thirty files.
Delete
Users can set the amount of time elapsed before the HDB file is deleted. The default and recommended setting is 'Never'.
