On Mon, Jul 17, 2017 at 3:22 AM, Alexander Korotkov
<a.korot...@postgrespro.ru> wrote:
> I think that "retail index tuple deletion" is the feature which could give
> us some advantages even independently from pluggable storages.  For example,
> imagine very large table with only small amount of dead tuples.  In this
> case, it would be cheaper to delete index links to those dead tuples one by
> one using "retail index tuple deletion", rather than do full scan of every
> index to perform "bulk delete" of index tuples.  One may argue that you
> shouldn't do vacuum of large table when only small amount of tuples are
> dead.  But in terms of index bloat mitigation, very aggressive vacuum
> strategy could be justified.

Yes, definitely. Especially with the visibility map. Even still, I
tend to think that for unique indexes, true duplicates should be
disallowed, and dealt with with an additional layer of indirection. So
this would be for secondary indexes.

>> I agree with Robert that being able to store an arbitrary payload as a
>> TID is probably not going to ever work very well.
> Support of arbitrary payload as a TID doesn't sound easy.  However, that
> doesn't mean it's unachievable. For me, it's more like long way which could
> be traveled step by step.

To be fair, it probably is achievable. Where there is a will, there is
a way. I just think that it will be easier to find a different way of
realizing similar benefits. I'm mostly talking about benefits around
making it cheap to have many secondary indexes by having logical
indirection instead of physical pointers (doesn't *have* to be
user-visible primary key values). HOT simply isn't effective enough at
preventing UPDATE index tuple insertions for indexes on unchanged
attributes, often just because pruning can fail to happen in time,
which WARM will not fix.

Peter Geoghegan

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