From af988635d49495fe622ab92578c88073524689f4 Mon Sep 17 00:00:00 2001
From: Gagan Goel <gagan.nith@gmail.com>
Date: Sun, 1 Sep 2019 23:22:10 -0400
Subject: [PATCH] 1. Execution plan now sets limitNum and limitOffset for all
 cases if an explicit limit is supplied in the query. 2. Fallback to using
 sql_select_limit system variable value if an explicit limit is not supplied.
 3. Remove checks that did not allow (2^64 - 1) as a valid limit value.

---
 dbcon/joblist/jlf_subquery.cpp      |  4 ----
 dbcon/joblist/joblistfactory.cpp    | 35 +++++++++++++----------------
 dbcon/mysql/ha_calpont_execplan.cpp | 23 +++++--------------
 3 files changed, 20 insertions(+), 42 deletions(-)

diff --git a/dbcon/joblist/jlf_subquery.cpp b/dbcon/joblist/jlf_subquery.cpp
index d08f700c4..3adfdb508 100644
--- a/dbcon/joblist/jlf_subquery.cpp
+++ b/dbcon/joblist/jlf_subquery.cpp
@@ -767,10 +767,6 @@ int doFromSubquery(CalpontExecutionPlan* ep, const string& alias, const string&
 
 void addOrderByAndLimit(CalpontSelectExecutionPlan* csep, JobInfo& jobInfo)
 {
-    // make sure there is a LIMIT
-    if (csep->orderByCols().size() > 0 && csep->limitNum() == (uint64_t) - 1)
-        return;
-
     jobInfo.limitStart = csep->limitStart();
     jobInfo.limitCount = csep->limitNum();
 
diff --git a/dbcon/joblist/joblistfactory.cpp b/dbcon/joblist/joblistfactory.cpp
index b4cbafee0..26242640e 100644
--- a/dbcon/joblist/joblistfactory.cpp
+++ b/dbcon/joblist/joblistfactory.cpp
@@ -1712,29 +1712,24 @@ void parseExecutionPlan(CalpontSelectExecutionPlan* csep, JobInfo& jobInfo,
 void makeVtableModeSteps(CalpontSelectExecutionPlan* csep, JobInfo& jobInfo,
                          JobStepVector& querySteps, JobStepVector& projectSteps, DeliveredTableMap& deliverySteps)
 {
-    // @bug4848, enhance and unify limit handling.
-    if (csep->limitNum() != (uint64_t) - 1)
+    // special case for outer query order by limit -- return all
+    if (jobInfo.subId == 0 && csep->hasOrderBy() && !csep->specHandlerProcessed())
     {
-        // special case for outer query order by limit -- return all
-        if (jobInfo.subId == 0 && csep->hasOrderBy() && !csep->specHandlerProcessed())
-        {
-            jobInfo.limitCount = (uint64_t) - 1;
-        }
+        jobInfo.limitCount = (uint64_t) - 1;
+    }
 
-        // support order by and limit in sub-query/union or
-        // GROUP BY handler processed outer query order
-        else if (csep->orderByCols().size() > 0)
-        {
-            addOrderByAndLimit(csep, jobInfo);
-        }
-
-        // limit without order by in any query
-        else
-        {
-            jobInfo.limitStart = csep->limitStart();
-            jobInfo.limitCount = csep->limitNum();
-        }
+    // support order by and limit in sub-query/union or
+    // GROUP BY handler processed outer query order
+    else if (csep->orderByCols().size() > 0)
+    {
+        addOrderByAndLimit(csep, jobInfo);
+    }
 
+    // limit without order by in any query
+    else
+    {
+        jobInfo.limitStart = csep->limitStart();
+        jobInfo.limitCount = csep->limitNum();
     }
 
     // Bug 2123.  Added overrideLargeSideEstimate parm below.  True if the query was written
diff --git a/dbcon/mysql/ha_calpont_execplan.cpp b/dbcon/mysql/ha_calpont_execplan.cpp
index 93ce8a46e..4fb54198f 100644
--- a/dbcon/mysql/ha_calpont_execplan.cpp
+++ b/dbcon/mysql/ha_calpont_execplan.cpp
@@ -7842,26 +7842,13 @@ int getSelectPlan(gp_walk_info& gwi, SELECT_LEX& select_lex,
                 }
             }
 
-            // relate to bug4848. let mysql drive limit when limit session variable set.
-            // do not set in csep. @bug5096. ignore session limit setting for dml
-            if (gwi.thd->variables.select_limit == (uint64_t) - 1 &&
-                !csep->hasOrderBy())
-            {
-                csep->limitStart(limitOffset);
-                csep->limitNum(limitNum);
-            }
-            // Pushdown queries w ORDER BY and LIMIT
-            else if (isPushdownHand && csep->hasOrderBy())
-            {
-                csep->limitStart(limitOffset);
-                csep->limitNum(limitNum);
-            }
+            csep->limitStart(limitOffset);
+            csep->limitNum(limitNum);
         }
-        // Pushdown queries with ORDER BY w/o explicit limit
-        else if (isPushdownHand && csep->hasOrderBy())
+        // If an explicit limit is not specified, use the system variable value
+        else
         {
-            // We must set this to activate LimitedOrderBy in ExeMgr
-            csep->limitNum((uint64_t) - 2);
+            csep->limitNum(gwi.thd->variables.select_limit);
         }
 
         // We don't currently support limit with correlated subquery