external
/
citus
mirror of https://github.com/citusdata/citus.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

More documentation and stale comments rewritten

pull/2572/head
Hanefi Onaldi 2019-02-04 19:12:51 +03:00
parent 825666f912
commit 148dcad0bb
No known key found for this signature in database
GPG Key ID: 95177DABDC09D1F5
1 changed files with 24 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
src/backend/distributed/planner/recursive_planning.c
View File

@ -1314,10 +1314,12 @@ ContainsReferencesToOuterQueryWalker(Node *node, VarLevelsUpWalkerContext *conte
/* /*
* WrapFunctionsInSubqueries iterates over all the immediate Range Table Entries * 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 * We wrap all the functions that are used in joins except the ones that are
* function returns records or a table we leave it as it is * laterally joined or have WITH ORDINALITY clauses.
* */ * */
static void static void
WrapFunctionsInSubqueries(Query *query) WrapFunctionsInSubqueries(Query *query)
@ -1325,12 +1327,25 @@ WrapFunctionsInSubqueries(Query *query)
List *rangeTableList = query->rtable; List *rangeTableList = query->rtable;
ListCell *rangeTableCell = NULL; 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) if (list_length(rangeTableList) < 2)
{ {
return; return;
} }
/* iterate over all RTEs and wrap them if necessary */
foreach(rangeTableCell, rangeTableList) foreach(rangeTableCell, rangeTableList)
{ {
RangeTblEntry *rangeTableEntry = (RangeTblEntry *) lfirst(rangeTableCell); RangeTblEntry *rangeTableEntry = (RangeTblEntry *) lfirst(rangeTableCell);
@ -1407,12 +1422,14 @@ TransformFunctionRTE(RangeTblEntry *rangeTblEntry)
* The indexing of attributes and TupleDesc and varattno differ * The indexing of attributes and TupleDesc and varattno differ
* *
* varattno=0 corresponds to whole row * 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, targetColumn = makeVar(1, targetColumnIndex + 1, columnType, -1, InvalidOid,
0); 0);
targetEntry = makeTargetEntry((Expr *) targetColumn, targetColumnIndex + 1, targetEntry = makeTargetEntry((Expr *) targetColumn, targetColumnIndex + 1,
columnName, columnName, false);
false);
subquery->targetList = lappend(subquery->targetList, targetEntry); subquery->targetList = lappend(subquery->targetList, targetEntry);
} }
} }