Andres Freund <and...@anarazel.de> writes: > On 2016-06-02 18:41:00 +0100, Greg Stark wrote: >> Well there's not *nothing* we can do. I thought I we were going to >> have to go back and do manual offset calculations to get that right.
> The kernel accesses the elements as an array. If the array stride (by > virtue of sizeof) were wrong, we couldn't fix that. Right. The general rule in C is that sizeof(anything) is always a multiple of the something's alignment requirement, so that if you have a correctly aligned initial element of an array then later elements are also correctly aligned. The problem in our existing code is that sizeof(WaitEventSet) might not be a multiple of the alignment requirement of WaitEvent, and either of those two might not be a multiple of the alignment requirement of struct epoll_event, etc. So we should make the code look like sz += MAXALIGN(sizeof(WaitEventSet)); sz += MAXALIGN(sizeof(WaitEvent) * nevents); #if defined(WAIT_USE_EPOLL) sz += MAXALIGN(sizeof(struct epoll_event) * nevents); etc, so that each of the subsidiary arrays starts on a MAXALIGN boundary. Where the later array elements fall is taken care of given that. regards, tom lane -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers