On 2010-09-25 at 02:03 -0500, Brad Knowles wrote: > Yup. The mmap() system call on NFS is undefined, which means that Berkeley > DB, and any other software that uses mmap() cannot safely be used on NFS. > This is supposedly fixed in the latest versions of NFS, but I have yet to > have that claim actually demonstrated to me.
My recollection is that it's actually the flushing behaviour of writes to mmap()d memory that is undefined and not flushable and so can't be combined with locks, of any kind, for protecting access to data. You also can't predict order-of-writes, etc. So mmap() works just fine, as long as you're very certain that only one host is ever going to be accessing the file at any time. So a single dedicated host, with manual failover to a hot standby after taking down the normal server, would work. I'm not saying that I recommend this, but knowing the actual limitations can make a difference when you're trying to duct-tape your way out of a problem. -Phil _______________________________________________ Tech mailing list Tech@lopsa.org http://lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
