Re: Switching to 64-bit Bitmapsets

David Rowley <david.rowley@2ndquadrant.com> writes:
> On Thu, 20 Dec 2018 at 17:50, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Hm, are you thinking of making BITS_PER_BITMAPWORD match sizeof(Pointer)
>> or something like that?  That seems like a good compromise from here.

> Yeah, something along those lines.  I've implemented that in the attached.

Pushed with some fiddling with the comment.

I wasn't excited about the test case you offered --- on HEAD, it pretty
much all devolves to file access operations (probably, checking the
current length of all the child relations).  Instead I experimented
with an old test case I had for a complex-to-plan query, and got these
results:

HEAD, asserts off:

pgbench reports:
latency average = 11704.992 ms
tps = 0.085434 (including connections establishing)
tps = 0.085437 (excluding connections establishing)

Top hits according to perf:
+   65.42%    65.16%        158499  postmaster       postgres                       [.]
match_eclasses_to_foreign_key_col
+    6.85%     6.82%         16634  postmaster       postgres                       [.] bms_overlap
+    6.25%     6.22%         15173  postmaster       postgres                       [.]
generate_join_implied_equalities_for_ecs
+    3.91%     3.88%          9465  postmaster       postgres                       [.] make_canonical_pathkey
+    3.04%     3.01%          7351  postmaster       postgres                       [.] have_relevant_eclass_joinclause
+    2.06%     2.05%          4992  postmaster       postgres                       [.] bms_is_subset
+    1.19%     1.18%          2887  postmaster       postgres                       [.] equal
+    0.95%     0.95%          2309  postmaster       postgres                       [.] get_eclass_for_sort_expr
+    0.90%     0.90%          2189  postmaster       postgres                       [.] add_paths_to_joinrel

With patch:

latency average = 10741.595 ms
tps = 0.093096 (including connections establishing)
tps = 0.093099 (excluding connections establishing)

+   69.03%    68.76%        178278  postmaster       postgres                     [.] match_eclasses_to_foreign_key_col
+    5.85%     5.82%         15138  postmaster       postgres                     [.]
generate_join_implied_equalities_for_ecs
+    4.58%     4.55%         11842  postmaster       postgres                     [.] bms_overlap
+    4.38%     4.36%         11338  postmaster       postgres                     [.] make_canonical_pathkey
+    2.77%     2.75%          7155  postmaster       postgres                     [.] have_relevant_eclass_joinclause
+    1.30%     1.29%          3364  postmaster       postgres                     [.] equal
+    1.26%     1.25%          3261  postmaster       postgres                     [.] bms_is_subset
+    1.06%     1.05%          2722  postmaster       postgres                     [.] get_eclass_for_sort_expr
+    0.70%     0.70%          1813  postmaster       postgres                     [.] add_paths_to_joinrel

Ignoring the, um, elephant in the room, this shows a pretty clear win
for the performance of bms_overlap and bms_is_subset, confirming
the thesis that this change is worthwhile.

I'll start a separate thread about match_eclasses_to_foreign_key_col.

            regards, tom lane