Anyway, I think the partitioned table is the right and brilliant solution, because an index really isn't required. The actual pending partition will always remain quite small, and being a queue, it doesn't even matter how big it might grow, as long as new rows are inserted at the end and not in the middle of the data file and still there be some way of fast skip over the part of the dead rows at the beginning that have already been processed and moved away.
Good thing is, I don't worry about maintenance window. I have the leisure to simply tear down my design now and make a better design. What's 2 million transactions if I can re-process them at a rate of 80/s? 7 hours max. I am still in development. So, no need to worry about migration / transition acrobatics. So if I take Corey's steps and envision the final result, not worrying about the transition steps, then I understand this:
1. Create the Queue table partitioned on the pending column, this creates the partition with the pending jobs (on which I set the fillfactor kind of low, maybe 50) and the default partition with all the rest. Of course that allows people with a constant transaction volume to also partition on jobId or completionTime and move chunks out to cold archive storage. But that's beside the current point.
One question I have though: I imagine our pending partition heap file to now be essentially sequentially organized as a queue. New jobs are appended at the end, old jobs are at the beginning. As pending jobs become completed (pending = false) these initial rows will be marked as dead. So, while the number of live rows will remain small in that pending partition, sequential scans will have to skip over the dead rows in the beginning.
Of course vacuum eliminates dead rows, but unless I do vacuum full, it will not re-pack the live rows, and that requires an exclusive table lock. So, what is the benefit of vacuuming that pending partition? What I don't want is insertion of new jobs to go into open slots at the beginning of the file. I want them to be appended (in Oracle there is an INSERT /*+APPEND*/ hint for that. How does that work in PostgreSQL?
Ultimately that partition will amass too many dead rows, then what do I do? I don't think that the OS has a way to truncate files physically from the head, does it? I guess it could set the file pointer from the first block to a later block. But I don't know of an IOCTL/FCNTL command for that. On some OS there is a way of making blocks sparse again, is that how PostgreSQL might do it? Just knock out blocks as sparse from the front of the file?
