From 613dec7c92fd1c4b30f31382b17540fca9cda81c Mon Sep 17 00:00:00 2001
From: Marco Bubke <marco.bubke@qt.io>
Date: Sat, 16 May 2020 14:47:01 +0200
Subject: [PATCH] Sqlite: Tweaking reserve of values function

We now save the size of the maximum of all results. This can be improve
performance if the result set sizes are similar. If the very different
we will allocate to much memory. Because it is not changing any results
it's hard to test. We maybe should add benchmarks later.

Change-Id: I07227200076365b7fe4d0ac3951981469f9d454f
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
---
 src/libs/sqlite/sqlitebasestatement.h | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/src/libs/sqlite/sqlitebasestatement.h b/src/libs/sqlite/sqlitebasestatement.h
index 05fbfa625b4..4c4baa11b77 100644
--- a/src/libs/sqlite/sqlitebasestatement.h
+++ b/src/libs/sqlite/sqlitebasestatement.h
@@ -205,10 +205,12 @@ public:
     {
         Resetter resetter{*this};
         std::vector<ResultType> resultValues;
-        resultValues.reserve(reserveSize);
+        resultValues.reserve(std::max(reserveSize, m_maximumResultCount));
 
         while (BaseStatement::next())
-           emplaceBackValues<ResultTypeCount>(resultValues);
+            emplaceBackValues<ResultTypeCount>(resultValues);
+
+        setMaximumResultCount(resultValues.size());
 
         resetter.reset();
 
@@ -222,12 +224,14 @@ public:
     {
         Resetter resetter{*this};
         std::vector<ResultType> resultValues;
-        resultValues.reserve(reserveSize);
+        resultValues.reserve(std::max(reserveSize, m_maximumResultCount));
 
         bindValues(queryValues...);
 
         while (BaseStatement::next())
-           emplaceBackValues<ResultTypeCount>(resultValues);
+            emplaceBackValues<ResultTypeCount>(resultValues);
+
+        setMaximumResultCount(resultValues.size());
 
         resetter.reset();
 
@@ -241,7 +245,7 @@ public:
                                    const std::vector<QueryElementType> &queryValues)
     {
         std::vector<ResultType> resultValues;
-        resultValues.reserve(reserveSize);
+        resultValues.reserve(std::max(reserveSize, m_maximumResultCount));
 
         for (const QueryElementType &queryValue : queryValues) {
             Resetter resetter{*this};
@@ -250,6 +254,8 @@ public:
             while (BaseStatement::next())
                 emplaceBackValues<ResultTypeCount>(resultValues);
 
+            setMaximumResultCount(resultValues.size());
+
             resetter.reset();
         }
 
@@ -264,7 +270,7 @@ public:
     {
         using Container = std::vector<ResultType>;
         Container resultValues;
-        resultValues.reserve(reserveSize);
+        resultValues.reserve(std::max(reserveSize, m_maximumResultCount));
 
         for (const auto &queryTuple : queryTuples) {
             Resetter resetter{*this};
@@ -273,6 +279,8 @@ public:
             while (BaseStatement::next())
                 emplaceBackValues<ResultTypeCount>(resultValues);
 
+            setMaximumResultCount(resultValues.size());
+
             resetter.reset();
         }
 
@@ -427,6 +435,13 @@ private:
         bindTupleValuesElement(element, ColumnIndices());
     }
 
+    void setMaximumResultCount(std::size_t count)
+    {
+        m_maximumResultCount = std::max(m_maximumResultCount, count);
+    }
+
+public:
+    std::size_t m_maximumResultCount = 0;
 };
 
 } // namespace Sqlite