Hi Liya,
This will not work AFAIK. Consider the query "SELECT a FROM t WHERE b>1".
The top-level operator has only one column:
Root[$0]
Project[$0]
Filter[$1>1]
Scan[$0=a, $1=b]
If you invoke RelMdColumnOrigins on Root[$0], you will get [t.a], but miss
[t.b].
To my knowledge, rules are the only way to reliably. constrain columns
returned from the scan.
Regards,
Vladimir.
вт, 22 дек. 2020 г. в 05:14, Fan Liya <[email protected]>:
> Hi Bhavya,
>
> Sorry I am not sure if I fully understand your question.
>
> Let me try to answer it according to my understanding:
>
> 1. Through RelColumnMDOrigins, we can get the RelColumnOrigin object, which
> includes a RelOptTable object.
> 2. The table scan also has a RelOptTable object, and all table scans of the
> plan can be found (e.g. through a visitor)
> 3. With the information of 1 and 2, given any output column, we can get to
> know it is derived from which columns from which table scans.
> 4. With the information of 3, given a table scan, we can get to know which
> column is never used in any output columns, and such columns can be pruned.
>
> Best,
> Liya Fan
>
>
> On Mon, Dec 21, 2020 at 11:31 PM Bhavya Aggarwal <[email protected]>
> wrote:
>
> > Hi Liya,
> >
> > I had a look at the RelColumnMDOrigins and it is useful in determining
> > which columns are from which table but still I am not sure how can I get
> > the column information for TableScan without the rules. If you have any
> > specific example where we have used this approach will be really helpful
> to
> > me.
> >
> > Thanks and regards
> > Bhavya
> >
> > On Mon, Dec 21, 2020 at 5:53 PM Fan Liya <[email protected]> wrote:
> >
> > > Hi Bhavya,
> > >
> > > IMO, to solve the problem from a global view, the following steps needs
> > to
> > > be taken:
> > >
> > > 1. Generate a physical plan in the original way (without considering
> > column
> > > pruning in the table scan)
> > > 2. Modify all the table scans in the plan with the RelColumnMDOrigins
> > > utility (the details have been described above)
> > > 3. Post process the plan with one of the following ways:
> > > a) a plan visitor that adjusts other operators in the tree.
> > > b) a light-weight planner (Hep or Volcano with limited rule sets)
> > >
> > > Run the query with the finally generated plan.
> > >
> > > Best,
> > > Liya Fan
> > >
> > >
> > > On Mon, Dec 21, 2020 at 3:33 PM Bhavya Aggarwal <[email protected]>
> > > wrote:
> > >
> > > > Hi Fan,
> > > >
> > > > I looked at the class RelColumnMDOrigins and it is giving me the
> origin
> > > of
> > > > the column, but even if I want to take it as a global decision I am
> not
> > > > sure how to proceed. Can you please elaborate on how to achieve this
> ?
> > I
> > > am
> > > > literally stuck as I do not want to use so many rules as in any case
> I
> > > have
> > > > to pass these to the TableScan, even if the user does a select * from
> > > > table, I need to add all those columns to the table scan.
> > > >
> > > > Regards
> > > > Bhavya
> > > >
> > > > --
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> > >
> >
> >
> > --
> > *Bhavya Aggarwal*
> > CTO & Partner
> > Knoldus Inc. <http://www.knoldus.com/>
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> > Canada - USA - India - Singapore
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> >
> > --
> > Your feedback matters - At Knoldus we aim to be very professional in our
> > quality of work, commitment to results, and proactive communication. If
> > you
> > feel otherwise please share your feedback
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> >
>
