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

On Tue, Mar 19, 2024 at 6:40 PM John Naylor <johncnaylorls(at)gmail(dot)com> wrote:
>
> On Tue, Mar 19, 2024 at 10:24 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > On Tue, Mar 19, 2024 at 8:35 AM John Naylor <johncnaylorls(at)gmail(dot)com> wrote:
> > >
> > > On Mon, Mar 18, 2024 at 11:12 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > > >
> > > > On Sun, Mar 17, 2024 at 11:46 AM John Naylor <johncnaylorls(at)gmail(dot)com> wrote:
>
> > > It might also be worth reducing the number of blocks in the random
> > > test -- multiple runs will have different offsets anyway.
> >
> > Yes. If we reduce the number of blocks from 1000 to 100, the
> > regression test took on my environment:
> >
> > 1000 blocks : 516 ms
> > 100 blocks : 228 ms
>
> Sounds good.
>
> > Removed some unnecessary variables in 0002 patch.
>
> Looks good.
>
> > So the MaxBlocktableEntrySize calculation would be as follows?
> >
> > #define MaxBlocktableEntrySize \
> > offsetof(BlocktableEntry, words) + \
> > (sizeof(bitmapword) * \
> > WORDS_PER_PAGE(Min(MaxOffsetNumber, \
> > BITS_PER_BITMAPWORD * PG_INT8_MAX - 1))))
> >
> > I've made this change in the 0003 patch.
>
> This is okay, but one side effect is that we have both an assert and
> an elog, for different limits. I think we'll need a separate #define
> to help. But for now, I don't want to hold up tidstore further with
> this because I believe almost everything else in v74 is in pretty good
> shape. I'll save this for later as a part of the optimization I
> proposed.
>
> Remaining things I noticed:
>
> +#define RT_PREFIX local_rt
> +#define RT_PREFIX shared_rt
>
> Prefixes for simplehash, for example, don't have "sh" -- maybe "local/shared_ts"
>
> + /* MemoryContext where the radix tree uses */
>
> s/where/that/
>
> +/*
> + * Lock support functions.
> + *
> + * We can use the radix tree's lock for shared TidStore as the data we
> + * need to protect is only the shared radix tree.
> + */
> +void
> +TidStoreLockExclusive(TidStore *ts)
>
> Talking about multiple things, so maybe a blank line after the comment.
>
> With those, I think you can go ahead and squash all the tidstore
> patches except for 0003 and commit it.
>
> > While reviewing the vacuum patch, I realized that we always pass
> > LWTRANCHE_SHARED_TIDSTORE to RT_CREATE(), and the wait event related
> > to the tidstore is therefore always the same. I think it would be
> > better to make the caller of TidStoreCreate() specify the tranch_id
> > and pass it to RT_CREATE(). That way, the caller can specify their own
> > wait event for tidstore. The 0008 patch tried this idea. dshash.c does
> > the same idea.
>
> Sounds reasonable. I'll just note that src/include/storage/lwlock.h
> still has an entry for LWTRANCHE_SHARED_TIDSTORE.

Thank you. I've incorporated all the comments above. I've attached the
latest patches, and am going to push them (one by one) after
self-review again.

Regards,

--
Masahiko Sawada
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