Github user DaveBirdsall commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/30#discussion_r34824459
--- Diff: core/sql/ustat/hs_globals.cpp ---
@@ -5364,9 +5368,31 @@ Lng32 HSGlobalsClass::CollectStatistics()
//
ISMemPercentage_ =
(float)CmpCommon::getDefaultNumeric(USTAT_IS_MEMORY_FRACTION);
- NABoolean trySampleTableBypassForIS = useSampling && multiGroup ==
NULL &&
- externalSampleTable == FALSE;
- // Don't bypass sampling for internal sort when MC stats
requested.
+ NABoolean trySampleTableBypassForIS = useSampling &&
externalSampleTable == FALSE;
+
+ mapInternalSortTypes(singleGroup);
+ Int64 maxRowsToRead = getInternalSortMemoryRequirements(TRUE);
+ // row count may be adjusted up if DP2 sampling and heavy amount
of varchars.
+
+ if (trySampleTableBypassForIS && multiGroup ) {
+
+ if (CmpCommon::getDefault(USTAT_USE_INTERNAL_SORT_FOR_MC) ==
DF_ON &&
+ allGroupsFitInMemory())
+ {
+ // if both single and MC groups can fit in memory, turn on
+ // performing MC in memory flag.
+ //
+ // Do not have to set the flag for next call to this
function
+ // (HSGlobalsClass::CollectStatistics()) since it is not
static and
+ // therefore a new HSGlobalsClass object will be
constructed.
+ // In HSGlobalsClass::HSGlobalsClass(), the flag is set to
FALSE.
+ setPerformISForMC(TRUE);
--- End diff --
OK, I think this likely answers my previous question
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