Thread: 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@optionshouse.com ______________________________________________ See http://www.peak6.com/email_disclaimer/ for terms and conditions related to this email
Shaun Thomas <sthomas@optionshouse.com> writes:
> Yet there's only one global setting for random_page_cost, and
> seq_page_cost, and so on.
We've had tablespace-specific settings for those for some time.
regards, tom lane
On 10/19/2012 09:51 AM, Tom Lane wrote: > We've had tablespace-specific settings for those for some time. Ah, my apologies. I didn't see any in the CREATE TABLESPACE page, and didn't think to check ALTER TABLESPACE. I withdraw my question. :) -- Shaun Thomas OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604 312-444-8534 sthomas@optionshouse.com ______________________________________________ See http://www.peak6.com/email_disclaimer/ for terms and conditions related to this email
On Fri, Oct 19, 2012 at 7:29 AM, Shaun Thomas <sthomas@optionshouse.com> wrote: > 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? Been done already: http://www.postgresql.org/docs/9.0/static/sql-altertablespace.html Cheers, Jeff
On 10/19/2012 10:05 AM, Jeff Janes wrote: > http://www.postgresql.org/docs/9.0/static/sql-altertablespace.html Yep. I realized my error was not checking the ALTER page after going through CREATE. I swore I remembered seeing it in the past, but was surprised it wasn't there. I keep forgetting Postgres prefers a CREATE + ALTER style than overloading every CREATE with all ALTER options. Though in my opinion that just adds extra unnecessary steps. -- Shaun Thomas OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604 312-444-8534 sthomas@optionshouse.com ______________________________________________ See http://www.peak6.com/email_disclaimer/ for terms and conditions related to this email
On Fri, Oct 19, 2012 at 8:07 AM, Shaun Thomas <sthomas@optionshouse.com> wrote: > On 10/19/2012 10:05 AM, Jeff Janes wrote: > >> http://www.postgresql.org/docs/9.0/static/sql-altertablespace.html > > > Yep. I realized my error was not checking the ALTER page after going through > CREATE. I swore I remembered seeing it in the past, but was surprised it > wasn't there. When I didn't see it under CREATE, I went to the docs page for the global page_cost settings, and that page directed me to the ALTER for the tablespace specific ones. It does seem like a statement in the CREATION page indicating that more options are available only via the ALTER of an already existing tablespace would be beneficial. > I keep forgetting Postgres prefers a CREATE + ALTER style than overloading > every CREATE with all ALTER options. Though in my opinion that just adds > extra unnecessary steps. I was surprised by the absence of the option in CREATE. I didn't recognize that as a general pgsql pattern though, I just thought it was peculiar to tablespaces. But I haven't surveyed the universe of create and alter commands. Cheers, Jeff