SERVER-65192 Implement ColumnShredder to extract paths and cells for a document

1 files changed, 111 insertions, 0 deletions

diff --git a/src/mongo/db/index/column_key_generator.h b/src/mongo/db/index/column_key_generator.h
new file mode 100644
index 00000000000..d88e642ff0d
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+++ b/src/mongo/db/index/column_key_generator.h
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+/**
+ *    Copyright (C) 2022-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+#include <iosfwd>
+
+#include "mongo/db/storage/column_store.h"
+#include "mongo/util/functional.h"
+
+namespace mongo::column_keygen {
+/**
+ * This is a representation of the cell prior to flattening it out into a buffer which is passed to
+ * visitor callbacks.
+ *
+ * All memory within the UnencodedCellView should only be assumed valid within the callback. If you
+ * need it longer, you must copy it yourself. Non-test callers will generally immediately encode
+ * this to a flat buffer, so this shouldn't be a problem.
+ */
+struct UnencodedCellView {
+    const std::vector<BSONElement>& vals;
+    StringData arrayInfo;
+
+    // If true, this path has multiple values in a single (possibly nested) object with the same
+    // field name. In this case, arrayInfo will be empty and this cell must not be used to
+    // reconstruct an object. We should probably not attempt to encode vals in the index either, and
+    // just put a marker that causes us to either skip the row (because it breaks the rules) or go
+    // to the row store.
+    //
+    // Note that this detection is best-effort and will only detect cases that would result in
+    // corrupt array info. We have decided that query results do not need to be precise for objects
+    // with duplicate fields, so it is OK if we don't detect every case, as long as we don't crash
+    // or cause corruption on the undetected cases.
+    bool hasDuplicateFields;
+
+    // If true, this cell omits values that are stored in subpaths.
+    bool hasSubPaths;
+
+    // If true, when reconstructing an object, you will need to visit the parent path in order to
+    // match current semantics for projections and field-path expressions.
+    bool isSparse;
+
+    // If true, at least one of the values in vals is inside of a directly-double-nested array, or
+    // the field name was encountered while already inside of a directly-double-nested array, so
+    // arrayInfo must be consulted to know which values to skip when matching. If false, simple
+    // matches can ignore the array info and just match against each value independently.
+    bool hasDoubleNestedArrays;
+
+    // These are only used in tests and for debugging.
+    friend bool operator==(const UnencodedCellView&, const UnencodedCellView&);
+    friend std::ostream& operator<<(std::ostream&, const UnencodedCellView&);
+    friend std::ostream& operator<<(std::ostream&, const UnencodedCellView*);
+};
+
+/**
+ * Visits all paths within obj and provides their cell values.
+ * Path visit order is unspecified.
+ */
+void visitCellsForInsert(const BSONObj& obj,
+                         function_ref<void(PathView, const UnencodedCellView&)> cb);
+
+/**
+ * Visits all paths within obj. When deleting, you do not need to know about values.
+ * Path visit order is unspecified.
+ */
+void visitPathsForDelete(const BSONObj& obj, function_ref<void(PathView)> cb);
+
+/**
+ * See visitDiffForUpdate().
+ */
+enum DiffAction { kInsert, kUpdate, kDelete };
+
+/**
+ * Computes differences between oldObj and newObj, and invokes cb() with the required actions to
+ * take to update the columnar index.
+ *
+ * For kInsert and kUpdate, the UnencodedCellView will point to the cell data for newObj (you
+ * don't need to know the value for oldObj).
+ *
+ * For kDelete, the UnencodedCellView pointer will be null.
+ *
+ * Path visit order is unspecified.
+ */
+void visitDiffForUpdate(const BSONObj& oldObj,
+                        const BSONObj& newObj,
+                        function_ref<void(DiffAction, PathView, const UnencodedCellView*)> cb);
+
+}  // namespace mongo::column_keygen