Re: [PoC] Improve dead tuple storage for lazy vacuum - Mailing list pgsql-hackers

On Tue, Jun 27, 2023 at 5:20 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Fri, Jun 23, 2023 at 6:54 PM John Naylor
> <john.naylor@enterprisedb.com> wrote:
> >
> >
> > I wrote:
> > > I cleaned up a few things and attached v34 so you can do that if you like.
> >
> > Of course, "clean" is a relative term. While making a small bit of progress working in tidbitmap.c earlier this
week,I thought it useful to prototype some things in the tidstore, at which point I was reminded it no longer compiles
becauseof my recent work. I put in the necessary incantations so that the v32 tidstore compiles and passes tests, so
here'sa patchset for that (but no vacuum changes). I thought it was a good time to also condense it down to look more
similarto previous patches, as a basis for future work. 
> >
>
> Thank you for updating the patch set. I'll look at updates closely
> early next week.
>

I've run several benchmarks for v32, where before your recent change
starting, and v35 patch. Overall the numbers are better than the
previous version. Here is the test result where I used 1-byte value:

"select * from bench_load_random(10_000_000)"

* v35
  radix tree leaves: 192 total in 0 blocks; 0 empty blocks; 0 free (0
chunks); 192 used
  radix tree node 256: 13697472 total in 205 blocks; 0 empty blocks;
52400 free (25 chunks); 13645072 used
  radix tree node 125: 86630592 total in 2115 blocks; 0 empty blocks;
7859376 free (6102 chunks); 78771216 used
  radix tree node 32: 94912 total in 0 blocks; 10 empty blocks; 0 free
(0 chunks); 94912 used
  radix tree node 15: 9269952 total in 1136 blocks; 0 empty blocks;
168 free (1 chunks); 9269784 used
  radix tree node 3: 1915502784 total in 233826 blocks; 0 empty
blocks; 6560 free (164 chunks); 1915496224 used
 mem_allocated | load_ms
---------------+---------
    2025194752 |    3011
(1 row)

* v32
  radix tree node 256: 192 total in 0 blocks; 0 empty blocks; 0 free
(0 chunks); 192 used
  radix tree node 256: 13487552 total in 205 blocks; 0 empty blocks;
51600 free (25 chunks); 13435952 used
  radix tree node 125: 192 total in 0 blocks; 0 empty blocks; 0 free
(0 chunks); 192 used
  radix tree node 125: 86630592 total in 2115 blocks; 0 empty blocks;
7859376 free (6102 chunks); 78771216 used
  radix tree node 32: 192 total in 0 blocks; 0 empty blocks; 0 free (0
chunks); 192 used
  radix tree node 32: 94912 total in 0 blocks; 10 empty blocks; 0 free
(0 chunks); 94912 used
  radix tree node 15: 192 total in 0 blocks; 0 empty blocks; 0 free (0
chunks); 192 used
  radix tree node 15: 9269952 total in 1136 blocks; 0 empty blocks;
168 free (1 chunks); 9269784 used
  radix tree node 3: 241597002 total in 29499 blocks; 0 empty blocks;
3864 free (161 chunks); 241593138 used
  radix tree node 3: 1809039552 total in 221696 blocks; 0 empty
blocks; 5280 free (110 chunks); 1809034272 used
 mem_allocated | load_ms
---------------+---------
    2160118410 |    3069
(1 row)

As you mentioned, the 1-byte value is embedded into 8 byte so 7 bytes
are unused, but we use less memory since we use less slab contexts and
save fragmentations.

I've also tested some large value cases (e.g. the value is 80-bytes)
and got a similar result.

Regarding the codes, there are many todo and fixme comments so it
seems to me that your recent work is still in-progress. What is the
current status? Can I start reviewing the code or should I wait for a
while until your recent work completes?

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com