From fe5d7920309ac836c7b45daa0f314de442c00636 Mon Sep 17 00:00:00 2001
From: Mathias Stearn <redbeard0531@gmail.com>
Date: Wed, 18 May 2022 11:24:44 +0000
Subject: SERVER-66314 improve columnar steady-state write impl

---
 src/mongo/db/index/column_key_generator.cpp | 45 +++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

(limited to 'src/mongo/db/index/column_key_generator.cpp')

diff --git a/src/mongo/db/index/column_key_generator.cpp b/src/mongo/db/index/column_key_generator.cpp
index aae01066cec..5002236eec3 100644
--- a/src/mongo/db/index/column_key_generator.cpp
+++ b/src/mongo/db/index/column_key_generator.cpp
@@ -102,6 +102,45 @@ public:
         }
     }
 
+    static void multiVisit(
+        const std::vector<BsonRecord>& recs,
+        function_ref<void(PathView, const BsonRecord& record, const UnencodedCellView&)> cb) {
+        const size_t count = recs.size();
+        if (count == 0)
+            return;
+
+        std::vector<ColumnShredder> shredders;
+        shredders.reserve(count);
+        for (auto&& rec : recs) {
+            shredders.emplace_back(*rec.docPtr);
+        }
+
+        if (count == 1) {
+            // Don't need to merge if just 1 record.
+            shredders[0].visitCells([&](PathView path, const UnencodedCellView& cell) {  //
+                cb(path, recs[0], cell);
+            });
+            return;
+        }
+
+        // Mapping: column name -> [raw cells and indexes to recs and shredders]
+        StringDataMap<std::vector<std::pair<RawCellValue*, size_t>>> columns;
+        for (size_t i = 0; i < count; i++) {
+            for (auto&& [path, rcv] : shredders[i]._paths) {
+                auto&& vec = columns[path];
+                if (vec.empty())
+                    vec.reserve(count);  // Optimize for columns existing in all records.
+                vec.emplace_back(&rcv, i);
+            }
+        }
+
+        for (auto&& [path, rows] : columns) {
+            for (auto&& [rcv, i] : rows) {
+                cb(path, recs[i], shredders[i].makeCellView(path, *rcv));
+            }
+        }
+    }
+
     static void visitDiff(const BSONObj& oldObj,
                           const BSONObj& newObj,
                           function_ref<void(DiffAction, PathView, const UnencodedCellView*)> cb) {
@@ -544,6 +583,12 @@ void visitCellsForInsert(const BSONObj& obj,
     ColumnShredder(obj).visitCells(cb);
 }
 
+void visitCellsForInsert(
+    const std::vector<BsonRecord>& recs,
+    function_ref<void(PathView, const BsonRecord& record, const UnencodedCellView&)> cb) {
+    ColumnShredder::multiVisit(recs, cb);
+}
+
 void visitPathsForDelete(const BSONObj& obj, function_ref<void(PathView)> cb) {
     ColumnShredder(obj, ColumnShredder::kOnlyPaths).visitPaths(cb);
 }
-- 
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