On Tue, Apr 24, 2012 at 9:40 PM, Robert Haas <robertmh...@gmail.com> wrote: > For three things, index pages > have hint-type changes that are not single-bit changes.
? Just how big are these? Part of the reason hint bit updates are safe is because one bit definitely absolutely has to be entirely in one page. You can't tear a page in the middle of a bit. In reality the size is much larger, probably 4k and almost certainly at least 512 bytes. But the postgres block layout doesn't really offer much guarantees about the location of anything relative those 512 byte blocks so probably anything larger than a word is unsafe to update. The main problem with the approach was that we kept finding more hint bits we had forgotten about. Once the coding idiom was established it seems it was a handy hammer for a lot of problems. -- greg -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
