Reserve capacity in some cases (#628)

Co-authored-by: Yee <2520865+yixinglu@users.noreply.github.com>

src/executor/query/DataCollectExecutor.cpp

@@ -109,6 +109,7 @@ Status DataCollectExecutor::rowBasedMove(const std::vector<std::string>& vars) {
     for (auto& var : vars) {
         auto& result = ectx_->getResult(var);
         auto iter = result.iter();
+        ds.rows.reserve(ds.rows.size() + iter->size());
         if (iter->isSequentialIter() || iter->isPropIter()) {
             auto* seqIter = static_cast<SequentialIter*>(iter.get());
             for (; seqIter->valid(); seqIter->next()) {

src/executor/query/DedupExecutor.cpp

@@ -29,6 +29,7 @@ folly::Future<Status> DedupExecutor::execute() {
     ResultBuilder builder;
     builder.value(iter->valuePtr());
     std::unordered_set<const LogicalRow*> unique;
+    unique.reserve(iter->size());
     while (iter->valid()) {
         if (!unique.emplace(iter->row()).second) {
             iter->unstableErase();

src/executor/query/ProjectExecutor.cpp

@@ -25,6 +25,7 @@ folly::Future<Status> ProjectExecutor::execute() {
     VLOG(1) << "input: " << project->inputVar();
     DataSet ds;
     ds.colNames = project->colNames();
+    ds.rows.reserve(iter->size());
     for (; iter->valid(); iter->next()) {
         Row row;
         for (auto& col : columns) {