On 21.02.2019 19:13, Robert Haas wrote:
> So I think it's better to have each backend locally make a decision
> about when that particular backend no longer needs the dictionary, and
> then let the system automatically clean up the ones that are needed by
> nobody.
Yep, it wouldn't be hard to implement.
> Perhaps a better approach still would be to do what Andres proposed
> back in March:
>
> #> Is there any chance we can instead can convert dictionaries into a form
> #> we can just mmap() into memory? That'd scale a lot higher and more
> #> dynamicallly?
>
> The current approach inherently involves double-buffering: you've got
> the filesystem cache containing the data read from disk, and then the
> DSM containing the converted form of the data. Having something that
> you could just mmap() would avoid that, plus it would become a lot
> less critical to keep the mappings around. You could probably just
> have individual queries mmap() it for as long as they need it and then
> tear out the mapping when they finish executing; keeping the mappings
> across queries likely wouldn't be too important in this case.
>
> The downside is that you'd probably need to teach resowner.c about
> mappings created via mmap() so that you don't leak mappings on an
> abort, but that's probably not a crazy difficult problem.
It seems to me Tom and Andres also vote for the mmap() approach. I think
I need to look closely at the mmap().
I've labeled the patch as 'v13'.
--
Arthur Zakirov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company
