Re: Expression errors with "FOR UPDATE" and postgres_fdw with partitionwise join enabled.
От | Etsuro Fujita |
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Тема | Re: Expression errors with "FOR UPDATE" and postgres_fdw with partitionwise join enabled. |
Дата | |
Msg-id | 5B1E5071.1000704@lab.ntt.co.jp обсуждение исходный текст |
Ответ на | Re: Expression errors with "FOR UPDATE" and postgres_fdw withpartition wise join enabled. (Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>) |
Ответы |
Re: Expression errors with "FOR UPDATE" and postgres_fdw withpartition wise join enabled.
(Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>)
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Список | pgsql-hackers |
(2018/06/07 19:42), Ashutosh Bapat wrote: > On Wed, Jun 6, 2018 at 5:00 PM, Etsuro Fujita > <fujita.etsuro@lab.ntt.co.jp> wrote: >> Since I'm not 100% sure that that is the right way to go, I've been >> rethinking how to fix this issue. Yet another idea I came up with to fix >> this is to redesign the handling of the tlists for children in the >> partitioning case. Currently, we build the reltarget for a child by >> applying adjust_appendrel_attrs to the reltarget for its parent in >> set_append_rel_size, which maps a wholerow Var referring to the parent rel >> to a ConvertRowtypeExpr that translates a wholerow of the child rel into a >> wholerow of the parent rel's rowtype. This works well for the >> non-partitioned inheritance case, but makes complicated the code for >> handling the partitioning case especially when planning partitionwise-joins. >> And I think this would be the root cause of this issue. > > Although true, this is not only about targetlist. Even the whole-row > expressions in the conditions, equivalence classes and other > planner/optimizer data structures are translated to > ConvertRowtypeExpr. Yeah, but I mean we modify set_append_rel_size so that we only map a parent wholerow Var in the parent tlist to a child wholerow Var in the child's tlist; parent wholerow Vars in the parent's other expressions such as conditions are transformed into CREs as-is. >> I don't think the >> tlists for the children need to have their wholerows transformed into the >> corresponding ConvertRowtypeExprs *at this point*, so what I'd like to >> propose is to 1) map a parent wholerow Var simply to a child wholerow Var, >> instead (otherwise, the same as adjust_appendrel_attrs), when building the >> reltarget for a child in set_append_rel_size, 2) build the tlists for child >> joins using those children's wholerow Vars at path creation time, and 3) >> adjust those wholerow Vars in the tlists for subpaths in the chosen >> AppendPath so that those are transformed into the corresponding >> ConvertRowtypeExprs, at plan creation time (ie, in >> create_append_plan/create_merge_append_plan). IIUC, this would not require >> any changes to pull_var_clause as proposed by the patch. This would not >> require any changes to postgres_fdw as proposed by the patch, either. In >> addition, this would make unnecessary the code added to setrefs.c by the >> partitionwise-join patch. Maybe I'm missing something though. > > Not translating whole-row expressions to ConvertRowtypeExpr before > creating paths can lead to a number of anomalies. For example, > > 1. if there's an index on the whole-row expression of child, > translating parent's whole-row expression to child's whole-row > expression as is will lead to using that index, when in reality the it > can not be used since the condition/ORDER BY clause (which originally > referred the parent's whole-row expression) require the child's > whole-row reassembled as parent's whole-row. > 2. Constraints on child'd whole-row expression, will be used to prune > a child when they can not be used since the original condition was on > parent' whole-row expression and not that of the child. > 3. Equivalence classes will think that a child whole-row expression > (without ConvertRowtypeExpr) is equivalent to an expression which is > part of the same equivalence class as the parent' whole-row > expression. Is that still possible when we only map a parent wholerow Var in the parent's tlist to a child wholerow Var in the child's tlist? Best regards, Etsuro Fujita
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