add unused sequence flag for non channel removal sequences

Author: gregns1

db/change_cache.go

@@ -453,6 +453,7 @@ func (c *changeCache) DocChanged(event sgbucket.FeedEvent) {
 			// the two conditions above together means that the cache expect ue to run processEntry on this sequence as its pending
 			// If seq >= c.getOldestSkippedSequence(ctx) and seq < current sequence allocated to the doc this means
 			// that this sequence never arrived over the caching feed due to deduplication and was pushed to a skipped sequence list
+			// We need check for 0 oldestSkipped because if the skipped list is empty 0 is returned
 			isSkipped := (seq < currentSequence && seq >= oldestSkipped) && oldestSkipped != 0
 			if (seq >= nextSequence && seq < currentSequence) || isSkipped {
 				base.InfofCtx(ctx, base.KeyCache, "Received deduplicated #%d in recent_sequences property for (%q / %q)", seq, base.UD(docID), syncData.CurrentRev)
@@ -469,7 +470,7 @@ func (c *changeCache) DocChanged(event sgbucket.FeedEvent) {
 					change.RevID = atRevId
 					change.Channels = channelRemovals
 				} else {
-					// Todo: add unused seq flag here (needs rebase)
+					change.UnusedSequence = true // treat as unused sequence when sequence is not channel removal
 				}
 
 				changedChannels := c.processEntry(ctx, change)