On Couchbase server 2.5.1 we store some temporary document items, with one-day expiry (.NET struct TimeSpan(1,0,0,0)). These items tend to have 10-20-minute update intervals so they have sliding expiration. When the external party in charge of the item fails to sent an update within an extended duration, we forcefully delete the item anyway and re-create another one.
For most part this perpetual update mechanism works fine. Once in a while, however, we observe the activity log the full list of items (obtained through a view) is less than expected. The document items just seem to “evaporate” from the bucket/view.
Since the update/refresh mechanisms are all happening in less than a day, it seems unlikely the document items would have crossed their expiry time. (To be safe at the moment the expiry is set to two days now). Is there something about time-limited items that might cause them to expiry from the bucket much quicker than set?
Occasionally we also observe the view dropping to a lesser count than actual document item count, and then “recovering” to full count on next check. What explains this fluctuating count in the view?