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.
Comments
Comment #1
catchOld but likely still valid. Worth backporting if it was a simple fix.
Comment #14
smustgrave CreditAttribution: smustgrave at Mobomo commentedWonder for D10 if this is still needed?