Hi, On 2020-06-05 16:56:44 -0600, Jens Axboe wrote: > On 6/5/20 4:54 PM, Andres Freund wrote: > > On 2020-06-05 16:49:24 -0600, Jens Axboe wrote: > >> Yes that's expected, if we have to fallback to ->readpage(), then it'll > >> go to a worker. read-ahead is what drives the async nature of it, as we > >> issue the range (plus more, depending on RA window) as read-ahead for > >> the normal read, then wait for it. > > > > But I assume async would still work for files with POSIX_FADV_RANDOM > > set, or not? Assuming the system wide setting isn't zero, of course. > > Yes it'll work if FADV_RANDOM is set. Cool. > But just not if read-ahead is totally disabled. I guess we could make > that work too, though not sure that it's super important. It's not from my end. I was just trying to check if the reduced performance I saw was related to interactions between PG prefetching and kernel level prefetching. And changing the /sys entry seemed easier than making postgres set POSIX_FADV_RANDOM... Greetings, Andres Freund
