When viewing a list of node teasers with comments, two queries are issued, one for node_last_viewed() to get the last timestamp, and the other to count how many new comments there are from comment_num_new().
At the least, we could use #636992: Entity loading needs protection from infinite recursion → (once it's in), to do a single query to get history records for all nodes on the page and stick it into a $node->last_viewed property, then in comment_node_view() use that for the comment_num_new() call.
Postponed: needs info
9.5
It affects performance. It is often combined with the Needs profiling tag.
After being applied to the 8.x branch, it should be considered for backport to the 7.x branch. Note: This tag should generally remain even after the backport has been written, approved, and committed.
Not all content is available!
It's likely this issue predates Contrib.social: some issue and comment data are missing.