Tablespace-derived stats?

Hello Perf,

Lately I've been pondering. As systems get more complex, it's not
uncommon for tiered storage to enter the picture. Say for instance, a
user has some really fast tables on a NVRAM-based device, and
slower-access stuff on a RAID, even slower stuff on an EDB, and variants
like local disk or a RAM drive.

Yet there's only one global setting for random_page_cost, and
seq_page_cost, and so on.

Would there be any benefit at all to adding these as parameters to the
tablespaces themselves? I can imagine the planner could override the
default with the tablespace setting on a per-table basis when
calculating the cost of retrieving rows from tables/indexes on faster or
slower storage.

This is especially true since each of the storage engines I listed have
drastically different performance profiles, but no way to hint to the
planner. There was a talk at the last PG Open about his EDB tests vastly
preferring partitioning and sequential access because random access was
so terrible. But NVRAM has the opposite metric. Currently, tuning for
one necessarily works against the other.

I didn't see anything in the Todo Wiki, so I figured I'd ask. :)

Thanks!

--
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-444-8534
sthomas(at)optionshouse(dot)com

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