When you get alot of messages in memory, we begin to page them to disk. This is a safeguard so we don't consume all the memory in the box. As consumers pull messages out of the queues, we pull messages out of the db and load them back in to memory.
The page ord is the order in which messages get pushed and pulled form the DB.
SELECT MESSAGE_ID, DELIVERY_COUNT, PAGE_ORD, SCHED_DELIVERY FROM JBM_MSG_REF WHERE CHANNEL_ID = ? AND PAGE_ORD BETWEEN ? AND ? ORDER BY PAGE_ORD
So we get the minimum page ord and we start from there. Each batch of page_refs we load, we add that many to the page ord we start with.
This error looks like the messages were removed somehow and made the ord numbes get out of sequence. Deleting the ord numbers are fine, they will renumber themselves.