Re: Heap WARM Tuples - Design Draft

On Thu, Aug 4, 2016 at 03:33:16PM -0300, Claudio Freire wrote:
> On Thu, Aug 4, 2016 at 3:23 PM, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote:
> >> That is a new HOT chain given our current code, but
> >> would the new tuple addition realize it needs to create a new index
> >> tuple? The new tuple code needs to check the index's root HOT tid for a
> >> non-match.
> >
> > I'm not proposing to change how HOT works, but adding another very
> > similar mechanism on top of it called WARM.
> >
> > So HOT will keep working like that, HOT pruning will happen as usual,
> > but we'll have the concept (immaterialized in the physical
> > representation of the data, just implicit) of WARM chains. WARM chains
> > would span one or several HOT chains, so they're "bigger".
>
>
> Answering your question, there's no need to find the root page on index updates.
>
> When creating the new tuple in nodeModifyTable.c, the code currently
> skips updating indexes if it's using HOT.
>
> We would add a check for WARM too. It will use WARM for index X iff both:
>
> * ItemPointerGetBlockNumber(oldtuplectid) ==
> ItemPointerGetBlockNumber(newtuplectid)
> * satisfies HOT for only this index X

OK, I see why you like walking the entire update chain instead of just
walking the HOT chain --- you think it avoids us having to find the HOT
chain root. However, how do you check the index to find out of the
update chain root is already in the index? I don't think you can just
look at the current tuple to know that since a previous tuple in the
update chain might have put it there even if the current old tuple
wouldn't have.

My point is there can be multiple update chains on the same page for
different rows with identical indexed values, so I don't see how
checking just for the page number helps here. Are we going to check the
entire page?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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