What do you say? Also I'm curious about Dr. Hipp meant in 2013 when talking about all the BSD:s and OpenBSD in particular at http://sqlite.1065341.n5.nabble.com/SQLite-3-7-17-preview-2x-faster-td68021.html by
"We have found that it does not work on OpenBSD, for reasons we have not yet been able to uncover; but as a precaution, memory mapped I/O is disabled by default on all of the *BSDs until we understand the problem. " Also I wonder if mmapping was switched on on the other BSD:s eventually. So basically: What's the problem/What was the problem. Thanks! 2015-05-22 13:47 GMT+05:30 Mikael <mikael.trash at gmail.com>: > > > 2015-05-22 13:28 GMT+05:30 Dan Kennedy <danielk1977 at gmail.com>: > >> On 05/22/2015 02:37 PM, Mikael wrote: >> >>> Hi, >>> >>> If mmap_size is big enough, read() will never be needed, so what about >>> enabling mmap on platforms that "lack of a unified buffer cache"? >>> >>> I mean, on a 64bit platform, setting mmap_size to say 1TB should be fine >>> - >>> >>> So what about enabling mmap_size on platforms that "lack of a unified >>> buffer cache"? >>> >>> >>> Also, if read() by some reason would be needed, there's msync() which is >>> like a flush(), so here the "lack of a unified buffer cache" shouldn't be >>> an issue anyhow? >>> >> >> I think part of the concern is two processes accessing the same SQLite >> database - one using mmap() and one using regular read() and write() calls. >> > > > You mean, the issue would be if two processes had the same SQLite database > opened and their mmap_size setting would be different? > > So SQLite already does msync() so the mmap+read()/write() is not actually > an issue within the scope of one OS process, that the mmap and readwrite > would go "out of sync" so you'd get data corruption that way? > > > Well if that's the only problem then I guess on OBSD mmap_size can safely > be turned on, just with that as precaution to the users i.e. all different > OS processes that open one and the same SQLite database *must* have the > *exactly* same mmap_size setting, or your file will be fried!? > > Sounds good to me! In particular that you can just put the mmap_size to > 1TB on all instances all over? > > (as at least on a 64bit machine you have 16.7 million 1TB address spaces > available so it's not like a scarce resource) > > >> Just out of interest, is it a specific platform that you're concerned >> about? >> > > OBSD just as specifically mentioned on https://www.sqlite.org/mmap.html ! > > >> Dan. >> >
