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Commit7a80e38

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Skip useless calculation of join RTE column names during EXPLAIN.
There's no need for set_simple_column_names() to compute uniquecolumn names for join RTEs, because a finished plan tree willnot contain any join alias Vars that we could need names for.Its other, internal callers will not pass it any join RTEsanyway, so the upshot is we can just skip join RTEs here.Aside from getting rid of a klugy against-its-documentation use ofset_relation_column_names, this can speed up EXPLAIN substantiallywhen considering many-join queries, because the upper join RTEstend to have a lot of columns.Sami Imseih, with cosmetic changes by meDiscussion:https://postgr.es/m/CAA5RZ0th3q-0p1pri58z9grG8r8azmEBa8o1rtkwhLmJg_cH+g@mail.gmail.com
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‎src/backend/utils/adt/ruleutils.c

Lines changed: 9 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -3773,9 +3773,8 @@ deparse_context_for_plan_tree(PlannedStmt *pstmt, List *rtable_names)
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dpns->appendrels=NULL;/* don't need it */
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/*
3776-
* Set up column name aliases. We will get rather bogus results for join
3777-
* RTEs, but that doesn't matter because plan trees don't contain any join
3778-
* alias Vars.
3776+
* Set up column name aliases, ignoring any join RTEs; they don't matter
3777+
* because plan trees don't contain any join alias Vars.
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*/
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set_simple_column_names(dpns);
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@@ -4067,8 +4066,10 @@ set_deparse_for_query(deparse_namespace *dpns, Query *query,
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*
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* This handles EXPLAIN and cases where we only have relation RTEs. Without
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* a join tree, we can't do anything smart about join RTEs, but we don't
4070-
* need to (note that EXPLAIN should never see join alias Vars anyway).
4071-
* If we do hit a join RTE we'll just process it like a non-table base RTE.
4069+
* need to, because EXPLAIN should never see join alias Vars anyway.
4070+
* If we find a join RTE we'll just skip it, leaving its deparse_columns
4071+
* struct all-zero. If somehow we try to deparse a join alias Var, we'll
4072+
* error out cleanly because the struct's num_cols will be zero.
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*/
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staticvoid
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set_simple_column_names(deparse_namespace*dpns)
@@ -4082,13 +4083,14 @@ set_simple_column_names(deparse_namespace *dpns)
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dpns->rtable_columns=lappend(dpns->rtable_columns,
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palloc0(sizeof(deparse_columns)));
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4085-
/* Assign unique column aliases within each RTE */
4086+
/* Assign unique column aliases within eachnon-joinRTE */
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forboth(lc,dpns->rtable,lc2,dpns->rtable_columns)
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{
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RangeTblEntry*rte= (RangeTblEntry*)lfirst(lc);
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deparse_columns*colinfo= (deparse_columns*)lfirst(lc2);
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4091-
set_relation_column_names(dpns,rte,colinfo);
4092+
if (rte->rtekind!=RTE_JOIN)
4093+
set_relation_column_names(dpns,rte,colinfo);
40924094
}
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}
40944096

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