Speed up the loading of row data a bit

MKleusberg · MKleusberg · commit 9c0b36d7b75a · 2019-05-02T12:34:14.000+02:00
This improves the performance for loading row data with my setup by
about 10%. Incidentally, the conversion from Qt to STL containers
reduced the performance by about the same number.
diff --git a/src/RowLoader.cpp b/src/RowLoader.cpp
@@ -234,18 +234,18 @@ void RowLoader::process (Task & t)
 
         while(!t.cancel && sqlite3_step(stmt) == SQLITE_ROW)
         {
-            Cache::value_type rowdata;
+            // Construct a new row object with the right number of columns
+            Cache::value_type rowdata(static_cast<size_t>(num_columns));
             for(int i=0;i<num_columns;++i)
             {
-                if(sqlite3_column_type(stmt, i) == SQLITE_NULL)
+                // No need to do anything for NULL values because we can just use the already default constructed value
+                if(sqlite3_column_type(stmt, i) != SQLITE_NULL)
                 {
-                    rowdata.emplace_back();
-                } else {
                     int bytes = sqlite3_column_bytes(stmt, i);
                     if(bytes)
-                        rowdata.emplace_back(static_cast<const char*>(sqlite3_column_blob(stmt, i)), bytes);
+                        rowdata[static_cast<size_t>(i)] = QByteArray(static_cast<const char*>(sqlite3_column_blob(stmt, i)), bytes);
                     else
-                        rowdata.emplace_back("");
+                        rowdata[static_cast<size_t>(i)] = "";
                 }
             }
             QMutexLocker lk(&cache_mutex);

Original file line number	Diff line number	Diff line change
`@@ -234,18 +234,18 @@ void RowLoader::process (Task & t)`
`234`	`234`
`235`	`235`	`while(!t.cancel && sqlite3_step(stmt) == SQLITE_ROW)`
`236`	`236`	`{`
`237`		`- Cache::value_type rowdata;`
	`237`	`+ // Construct a new row object with the right number of columns`
	`238`	`+ Cache::value_type rowdata(static_cast<size_t>(num_columns));`
`238`	`239`	`for(int i=0;i<num_columns;++i)`
`239`	`240`	`{`
`240`		`- if(sqlite3_column_type(stmt, i) == SQLITE_NULL)`
	`241`	`+ // No need to do anything for NULL values because we can just use the already default constructed value`
	`242`	`+ if(sqlite3_column_type(stmt, i) != SQLITE_NULL)`
`241`	`243`	`{`
`242`		`- rowdata.emplace_back();`
`243`		`- } else {`
`244`	`244`	`int bytes = sqlite3_column_bytes(stmt, i);`
`245`	`245`	`if(bytes)`
`246`		`- rowdata.emplace_back(static_cast<const char*>(sqlite3_column_blob(stmt, i)), bytes);`
	`246`	`+ rowdata[static_cast<size_t>(i)] = QByteArray(static_cast<const char*>(sqlite3_column_blob(stmt, i)), bytes);`
`247`	`247`	`else`
`248`		`- rowdata.emplace_back("");`
	`248`	`+ rowdata[static_cast<size_t>(i)] = "";`
`249`	`249`	`}`
`250`	`250`	`}`
`251`	`251`	`QMutexLocker lk(&cache_mutex);`