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

On Tue, Jan 30, 2024 at 7:56 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Mon, Jan 29, 2024 at 8:48 PM John Naylor <johncnaylorls(at)gmail(dot)com> wrote:

> > I meant the macro could probably be
> >
> > Max(SLAB_DEFAULT_BLOCK_SIZE, (size) * N)
> >
> > (Right now N=32). I also realize I didn't answer your question earlier
> > about block sizes being powers of two. I was talking about PG in
> > general -- I was thinking all block sizes were powers of two. If
> > that's true, I'm not sure if it's because programmers find the macro
> > calculations easy to reason about, or if there was an implementation
> > reason for it (e.g. libc behavior). 32*2088 bytes is about 65kB, or
> > just above a power of two, so if we did round that up it would be
> > 128kB.
>
> Thank you for your explanation. It might be better to follow other
> codes. Does the calculation below make sense to you?
>
> RT_SIZE_CLASS_ELEM size_class = RT_SIZE_CLASS_INFO[i];
> Size inner_blocksize = SLAB_DEFAULT_BLOCK_SIZE;
> while (inner_blocksize < 32 * size_class.allocsize)
> inner_blocksize <<= 1;

It does make sense, but we can do it more simply:

Max(SLAB_DEFAULT_BLOCK_SIZE, pg_nextpower2_32(size * 32))