Hi guys!
I came across something really interesting last week and I'm hoping someone can shed some light on my observation and guesses.
Background
We had a few heartbeat tags archiving heartbeat readings from our interfaces every 5 seconds for the past 1 year.
Those tags were incorrectly setup to archive as we use PE tags to monitor our interfaces by interrogating the previous event's timestamp of the heartbeat tags that we use, and it's the results of the PE tags we want to archive.
When I came across this, I started deleting all the useless (to us) heartbeat readings from the heartbeat tags.
That was about 19 million events over the span of one year, and performed the cleanup using the Archive Editor in SMT.
Now, compression on those tags was off, and out of curiosity I checked the size of the archive before the deletion and after the deletion to get a sense of the degree of impact the storage those readings had on our archives.
Much to my surprise, the archive sizes didn't change at all after the deletion was complete.
Reading though some KB articles on PI archives this morning, I decided to re-process two of our archives that contained data from the past 1 year, and thus would've contained the events from the heartbeat tags that were cleaned up.
Once I reprocessed the archives, their size was signficantly smaller (one was smaller by 100MB).
We do not delete tags, nor do we allow event deletions on non-admin tags as it's against our system policy (for audit purposes), thus I'm inclined to believe the only reason these archives shrunk is due to the deletion of the 19 million heartbeat events archived (fragmented of course across different archives based on the event timestamps).
Questions
1) If events are deleted via the Archive Editor plugin in PI SMT, are they are simply marked in the archive(s) as say "deleted", but are not really deleted (ie. removed from the archive(s))?
2) The only way tag readings/events are actually removed from archives is by reprocessing the archive(s) after having the events deleted in the Archive Editor plugin?
3) If events are removed using the piconfig tool, is the behavior the same as deleting events using the Archive Editor plugin? For example, using the commands:
@table piarc
@mode edit, t
@istr tag, time
@modi mode = remove
or does piconfig remove the events from the archive(s) without the need to reprocess?
Thanks a lot guys!
Cheers,
Mario