Patches from: aoki@CS.Berkeley.EDU (Paul M. Aoki)

i gave jolly my btree bulkload code a long, long time ago but never
gave him a bunch of my bugfixes.  here's a diff against the 6.0
baseline.

for some reason, this code has slowed down somewhat relative to the
insertion-build code on very small tables.  don't know why -- it used
to be within about 10%.  anyway, here are some (highly unscientific!)
timings on a dec 3000/300 for synthetic tables with 10k, 100k and
1000k tuples (basically, 1mb, 10mb and 100mb heaps).  'c' means
clustered (pre-sorted) inputs and 'u' means unclustered (randomly
ordered) inputs.  the 10k table basically fits in the buffer pool, but
the 100k and 1000k tables don't.  as you can see, insertion build is
fine if you've sorted your heaps on your index key or if your heap
fits in core, but is absolutely horrible on unordered data (yes,
that's 7.5 hours to index 100mb of data...) because of the zillions of
random i/os.

if it doesn't work for you for whatever reason, you can always turn it
back off by flipping the FastBuild flag in nbtree.c.  i don't have
time to maintain it.

good luck!

baseline code:

time psql -c 'create index c10 on k10 using btree (c int4_ops)' bttest
real   8.6
time psql -c 'create index u10 on k10 using btree (b int4_ops)' bttest
real   9.1
time psql -c 'create index c100 on k100 using btree (c int4_ops)' bttest
real   59.2
time psql -c 'create index u100 on k100 using btree (b int4_ops)' bttest
real   652.4
time psql -c 'create index c1000 on k1000 using btree (c int4_ops)' bttest
real   636.1
time psql -c 'create index u1000 on k1000 using btree (b int4_ops)' bttest
real   26772.9

bulkloading code:

time psql -c 'create index c10 on k10 using btree (c int4_ops)' bttest
real   11.3
time psql -c 'create index u10 on k10 using btree (b int4_ops)' bttest
real   10.4
time psql -c 'create index c100 on k100 using btree (c int4_ops)' bttest
real   59.5
time psql -c 'create index u100 on k100 using btree (b int4_ops)' bttest
real   63.5
time psql -c 'create index c1000 on k1000 using btree (c int4_ops)' bttest
real   636.9
time psql -c 'create index u1000 on k1000 using btree (b int4_ops)' bttest
real   701.0