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diff --git a/src/mongo/db/pipeline/doc_mem_monitor.h b/src/mongo/db/pipeline/doc_mem_monitor.h
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+/**
+ * Copyright 2011 (c) 10gen Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * 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
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "pch.h"
+#include "util/string_writer.h"
+
+
+namespace mongo {
+
+    /*
+      This utility class provides an easy way to total up, monitor, warn, and
+      signal an error when the amount of memory used for an operation exceeds
+      given thresholds.
+
+      Create a local instance of this class, and then inform it of any memory
+      that you consume using addToTotal().
+
+      Warnings or errors are issued as usage exceeds certain fractions of
+      physical memory on the host, as determined by SystemInfo.
+
+      This class is not guaranteed to warn or signal errors if the host system
+      does not support the ability to report its memory, as per the warnings
+      for SystemInfo in systeminfo.h.
+     */
+    class DocMemMonitor {
+    public:
+	/*
+	  Constructor.
+
+	  Uses default limits for warnings and errors.
+
+	  The StringWriter parameter must outlive the DocMemMonitor instance.
+
+	  @param pWriter string writer that provides information about the
+	      operation being monitored
+	 */
+	DocMemMonitor(StringWriter *pWriter);
+
+	/*
+	  Constructor.
+
+	  This variant allows explicit selection of the limits.  Note that
+	  limits of zero are treated as infinite.
+
+	  The StringWriter parameter must outlive the DocMemMonitor instance.
+
+	  @param pWriter string writer that provides information about the
+	      operation being monitored
+	  @param warnLimit the amount of ram to issue (log) a warning for
+	  @param errorLimit the amount of ram to throw an error for
+	 */
+	DocMemMonitor(StringWriter *pWriter, size_t warnLimit,
+		      size_t errorLimit);
+
+	/*
+	  Increment the total amount of memory used by the given amount.  If
+	  the warning threshold is exceeded, a warning will be logged.  If the
+	  error threshold is exceeded, an error will be thrown.
+
+	  @param amount the amount of memory to add to the current total
+	 */
+	void addToTotal(size_t amount);
+
+    private:
+	/*
+	  Real constructor body.
+
+	  Provides common construction for all the variant constructors.
+	 */
+	void init(StringWriter *pW, size_t warnLimit, size_t errorLimit);
+
+	bool warned;
+	size_t totalUsed;
+	size_t warnLimit;
+	size_t errorLimit;
+	StringWriter *pWriter;
+    };
+
+}