Re: Make tuple deformation faster

On Tue, 6 Aug 2024 at 13:11, David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
> I'll put this up for the CF bot to run with for a bit as the patch has
> needed a rebase since I pushed the v1-0001 patch.

I've been doing more work on this patch set as I'd been concerned
there wasn't any validation to ensure the TupleDesc's
FormData_pg_attribute and the CompactAttribute are kept in sync when
the TupleDesc is altered in various places around the codebase. To
make this more robust, in USE_ASSERT_CHECKING builds, I made it so the
TupleDescCompactAttr() macro is turned into an inline function with an
Assert to validate the stored CompactAttribute vs one freshly
populated from the FormData_pg_attribute. Doing this caused me to find
a missed call to populate_compact_attribute(), so was worth the
effort. There's no apparent performance difference when running all
the tests with and without this extra checking.

I also spent time doing performance tests using 3 different machines.
I didn't document the previous performance tests, but I expect I ran
them on my AMD 7945hx laptop. On testing again today, I used that
Zen4 laptop plus an AMD 3990x (Zen2) and a 10-core Apple M2. I found
that it was only the 7945hx laptop that was showing any decent gains
from this patch :(. After thinking for a bit, I decided to expand the
CompactAttribute.attflags where I'd been bit packing in 5 boolean
fields from pg_attribute and expand those into bool fields. This made
the performance much better. The 0005 contains this change
independently.

Please see the attached "patches-0001-0005_results.png". This shows
the test query running 25% faster on the 7945hx laptop with gcc. The
least gains were from the Apple M2 at about a 9-10% increase.

The "patches-0001-0004_results.png" shows the results with the smaller
bit-packed CompactAttriubute struct. You can see that without the 0005
patch, there are some performance regressions, so I propose including
0005 which widens CompactAttribute from 8 bytes to 16 bytes.

David