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More documentation and stale comments rewritten

pull/2572/head
Hanefi Onaldi 2019-02-04 19:12:51 +03:00
parent 825666f912
commit 148dcad0bb
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1 changed files with 24 additions and 7 deletions
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31
src/backend/distributed/planner/recursive_planning.c
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@ -1314,10 +1314,12 @@ ContainsReferencesToOuterQueryWalker(Node *node, VarLevelsUpWalkerContext *conte
/*
* WrapFunctionsInSubqueries iterates over all the immediate Range Table Entries
* of a query and wraps the functions inside (SELECT * FROM fnc() f) subqueries.
* of a query and wraps the functions inside (SELECT * FROM fnc() f)
* subqueries, so that those functions will be executed on the coordinator if
* necessary.
*
* We currently wrap only those functions that return a single value. If a
* function returns records or a table we leave it as it is
* We wrap all the functions that are used in joins except the ones that are
* laterally joined or have WITH ORDINALITY clauses.
* */
static void
WrapFunctionsInSubqueries(Query *query)
@ -1325,12 +1327,25 @@ WrapFunctionsInSubqueries(Query *query)
List *rangeTableList = query->rtable;
ListCell *rangeTableCell = NULL;
/* there needs to be at least two RTEs for a join operation */
/*
* If we have only one function call in a query without any joins, we can
* easily decide where to execute it.
*
* If there are some subqueries and/or functions that are joined with a
* function, it is not trivial to decide whether we should run this
* function in the coordinator or in workers and therefore we may need to
* wrap some of those functions in subqueries.
*
* If we have only one RTE, we leave the parsed query tree as it is. This
* also makes sure we do not wrap an already wrapped function call
* because we know that there will always be 1 RTE in a wrapped function.
* */
if (list_length(rangeTableList) < 2)
{
return;
}
/* iterate over all RTEs and wrap them if necessary */
foreach(rangeTableCell, rangeTableList)
{
RangeTblEntry *rangeTableEntry = (RangeTblEntry *) lfirst(rangeTableCell);
@ -1407,12 +1422,14 @@ TransformFunctionRTE(RangeTblEntry *rangeTblEntry)
* The indexing of attributes and TupleDesc and varattno differ
*
* varattno=0 corresponds to whole row
* varattno=1 corresponds to first column that is stored in tupDesc->attrs[0] */
* varattno=1 corresponds to first column that is stored in tupDesc->attrs[0]
*
* That's why we need to add one to the targetColumnIndex
* */
targetColumn = makeVar(1, targetColumnIndex + 1, columnType, -1, InvalidOid,
0);
targetEntry = makeTargetEntry((Expr *) targetColumn, targetColumnIndex + 1,
columnName,
false);
columnName, false);
subquery->targetList = lappend(subquery->targetList, targetEntry);
}
}