On Sat, Aug 13, 2016 at 1:18 AM, Andrew Gierth
<andrew@tao11.riddles.org.uk> wrote:
>
> Hmm? The code in _bt_findsplitloc and _bt_checksplitloc doesn't seem to
> agree with this.
>
> (Inserting on the high leaf page is a special case, which is where the
> fillfactor logic kicks in; that's why sequentially filled indexes are
> (by default) 90% full rather than 100%. But other pages split into
> roughly equal halves.)
Hm, I was going from this lore. I didn't realize it was only for
inserts near the end of the index. That's cleverer than I realized.
commit 1663f3383849968415d29965ef9bfdf5aac4d358
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat Sep 29 23:49:51 2001 +0000
Tweak btree page split logic so that when splitting a page that is rightmost on its tree level, we split 2/3 to
theleft and 1/3 to the new right page, rather than the even split we use elsewhere. The idea is that when faced
witha steadily increasing series of inserted keys (such as sequence or timestamp values), we'll end up with a btree
that's about 2/3ds full not 1/2 full, which is much closer to the desired steady-state load for a btree. Per
suggestionfrom Ann Harrison of IBPhoenix.
--
greg
