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
