On Mon, Jul 11, 2011 at 12:51 PM, Anish Kejariwal <anishkej(at)gmail(dot)com> wrote:
> The following bug has been logged online:
> Bug reference: 6112
> Logged by: Anish Kejariwal
> Email address: anishkej(at)gmail(dot)com
> PostgreSQL version: 9.0.3
> Operating system: Linux
> Description: heuristic for empty parent tables that are members of
> inheritance trees
> I'm filing this issue as a bug, and it seems like Tom Lane agrees that there
> is a bug, and said: " maybe we should reconsider the heuristic for tables
> that are members of inheritance trees --- particularly parents of
> inheritance trees."
> All information is in:
> -empty parent table
> -all data is in child/partitioned tables
> optimizer considers the parent table to be empty.
> Result: The execution plan is incorrect. My particularly query took 25
> seconds with the wrong execution plan, but 0.3 seconds with the correct
> execution plan.
> Work around:
> Tom Lane suggested the following workaround to "defeat the empty-table
> update pg_class set relpages = 1 where relname = 'icecream';
> I'm using this work around for now, but I don't think this is acceptable.
> If someone were to accidentally run vacuum analyze on the parent table, then
> the relpages will be set back to zero, and the query will run slowly.
> Please let me know if you have any questions.
Tom fixed this in commit f3ff0433ab32fdc69da3c8f8e691ef6b4366559c on July 14th.
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