hi to all, are there limits in writing through applications on PI data? Can I write even before the creation of the tag pi? Also is it possible to write future values?
The PI system stores data in files referred to as archives; each archive has a start time, and unless it is the primary (current) archive, and end time - for our purposes assume the end time for the primary archive is always now.
Data can be written into the archive for a time before the tag was created if the following conditions are met: an archive exists that has a start/end time within the time the data is to be written to and the archive is not marked as 'read-only'.
In PI Data Archive 2015 the concept of a 'future data' was created; a tag must be defined as a 'future' data tag in order to store values in the future.
OK thanks Tim. let's see if I understand. Based on the example table I cannot write before 7/22 because there are no archives. Furthermore, if the archive becomes full, the writing may not work.
In addition to Tim Carmichael's comment, please check out the resources below:https://livelibrary.osisoft.com/LiveLibrary/content/en/server-v12/GUID-34B800F0-CF34-4E44-A86A-B2094494696E
To answer your questions:1. You CAN write data before the point created dates. But please consult Kb00848 carefully if you are using 2010 or older versions of PI Data Archives: You may need to reprocess archives and this can take very long.
2. No future values are allowed in historical tags.
There are two types of PI tags at large; Historical and Future. You cannot write future values to historical tags. The data server does not accept it as a valid value. Instead, if you wish to keep predictions of value, please use future type tags.
The past predictions will remain in your future archives for further analysis. This will allow easier comparison between the actual outcome and predictions.
thank you so much Jinmo . based on the KB I should have no problem writing the historian. Right?
Yes if you are backfilling a tag, then just need to follow procedure lined out in the System management guide. You should be ok.
Retrieving data ...