Re: [PoC] Improve dead tuple storage for lazy vacuum

On Fri, Feb 16, 2024 at 10:05 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Thu, Feb 15, 2024 at 8:26 PM John Naylor <johncnaylorls(at)gmail(dot)com> wrote:

> > v61-0007: Runtime-embeddable tids -- Optional for v17, but should
> > reduce memory regressions, so should be considered. Up to 3 tids can
> > be stored in the last level child pointer. It's not polished, but I'll
> > only proceed with that if we think we need this. "flags" iis called
> > that because it could hold tidbitmap.c booleans (recheck, lossy) in
> > the future, in addition to reserving space for the pointer tag. Note:
> > I hacked the tests to only have 2 offsets per block to demo, but of
> > course both paths should be tested.
>
> Interesting. I've run the same benchmark tests we did[1][2] (the
> median of 3 runs):
[found a big speed-up where we don't expect one]

I tried to reproduce this (similar patch, but rebased on top of a bug
you recently fixed (possibly related?) -- attached, and also shows one
way to address some lack of coverage in the debug build, for as long
as we test that with CI).

Fortunately I cannot see a difference, so I believe it's not affecting
the case in this test all, as expected:

v68:

INFO: finished vacuuming "john.public.test": index scans: 1
pages: 0 removed, 442478 remain, 88478 scanned (20.00% of total)
tuples: 19995999 removed, 80003979 remain, 0 are dead but not yet removable
removable cutoff: 770, which was 0 XIDs old when operation ended
frozen: 0 pages from table (0.00% of total) had 0 tuples frozen
index scan needed: 88478 pages from table (20.00% of total) had
19995999 dead item identifiers removed
index "test_x_idx": pages: 274194 in total, 54822 newly deleted, 54822
currently deleted, 0 reusable
avg read rate: 620.356 MB/s, avg write rate: 124.105 MB/s
buffer usage: 758236 hits, 274196 misses, 54854 dirtied
WAL usage: 2 records, 0 full page images, 425 bytes

system usage: CPU: user: 3.74 s, system: 0.68 s, elapsed: 4.45 s
system usage: CPU: user: 3.02 s, system: 0.42 s, elapsed: 3.47 s
system usage: CPU: user: 3.09 s, system: 0.38 s, elapsed: 3.49 s
system usage: CPU: user: 3.00 s, system: 0.43 s, elapsed: 3.45 s

v68 + emb values (that cannot be used because > 3 tids per block):

INFO: finished vacuuming "john.public.test": index scans: 1
pages: 0 removed, 442478 remain, 88478 scanned (20.00% of total)
tuples: 19995999 removed, 80003979 remain, 0 are dead but not yet removable
removable cutoff: 775, which was 0 XIDs old when operation ended
frozen: 0 pages from table (0.00% of total) had 0 tuples frozen
index scan needed: 88478 pages from table (20.00% of total) had
19995999 dead item identifiers removed
index "test_x_idx": pages: 274194 in total, 54822 newly deleted, 54822
currently deleted, 0 reusable
avg read rate: 570.808 MB/s, avg write rate: 114.192 MB/s
buffer usage: 758236 hits, 274196 misses, 54854 dirtied
WAL usage: 2 records, 0 full page images, 425 bytes

system usage: CPU: user: 3.11 s, system: 0.62 s, elapsed: 3.75 s
system usage: CPU: user: 3.04 s, system: 0.41 s, elapsed: 3.46 s
system usage: CPU: user: 3.05 s, system: 0.41 s, elapsed: 3.47 s
system usage: CPU: user: 3.04 s, system: 0.43 s, elapsed: 3.49 s

I'll continue polishing the runtime-embeddable values patch as time
permits, for later consideration.