Re: Join push-down support for foreign tables

On Thu, Sep  4, 2014 at 09:31:20PM +0530, Atri Sharma wrote:
>     I am thinking we would eventually have to cache the statistics, then get
>     some kind of invalidation message from the foreign server.  I am also
>     thinking that cache would have to be global across all backends, I guess
>     similar to our invalidation cache.
> 
> 
> 
> 
> That could lead to some bloat in storing statistics since we may have a lot of
> tables for a lot of foreign servers. Also, will we have VACUUM look at
> ANALYZING the foreign tables?

> Also, how will we decide that the statistics are invalid? Will we have the FDW
> query the foreign server and do some sort of comparison between the statistics
> the foreign server has and the statistics we locally have? I am trying to
> understand how the idea of invalidation message from foreign server will work.

Well, ANALYZING is running on the foreign server, and somehow it would
be nice if it would send a message to us about its new statistics, or we
can do it like http does and it gives us a last-refresh statistics date
when we connect.

I am not sure how it will work --- I am just suspecting that we might
get to a point where the statistics lookup overhead on the foreign
server might become a bottleneck.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
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