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+<a id="tor-spec.txt-8"></a>
+# Handling resource exhaustion
+
+<a id="tor-spec.txt-8.1"></a>
+## Memory exhaustion.
+
+(See also dos-spec.md.)
+
+If RAM becomes low, an OR should begin destroying circuits until
+more memory is free again.  We recommend the following algorithm:
+
+- Set a threshold amount of RAM to recover at 10% of the total RAM.
+
+```text
+     - Sort the circuits by their 'staleness', defined as the age of the
+       oldest data queued on the circuit.  This data can be:
+
+          * Bytes that are waiting to flush to or from a stream on that
+            circuit.
+
+          * Bytes that are waiting to flush from a connection created with
+            BEGIN_DIR.
+
+          * Cells that are waiting to flush or be processed.
+
+     - While we have not yet recovered enough RAM:
+
+          * Free all memory held by the most stale circuit, and send DESTROY
+            cells in both directions on that circuit.  Count the amount of
+            memory we recovered towards the total.
+```
+