Merge #11011: [Trivial] Add a comment on the use of prevector in script.

08f71c2 [Trivial] Add a comment on the use of prevector in script. (Gregory Maxwell)

Pull request description:

Tree-SHA512: 020981516e67e576685eb9a8532178fb97d1780af409fc86d869cd05c293c0c823c26e838cf544d18610f5a3f479ce3e47d2ccb95fb1c4e55fe9e7ceb354f20b

Author: MarcoFalke

src/script/script.h

@@ -377,6 +377,12 @@ class CScriptNum
     int64_t m_value;
 };
 
+/**
+ * We use a prevector for the script to reduce the considerable memory overhead
+ *  of vectors in cases where they normally contain a small number of small elements.
+ * Tests in October 2015 showed use of this reduced dbcache memory usage by 23%
+ *  and made an initial sync 13% faster.
+ */
 typedef prevector<28, unsigned char> CScriptBase;
 
 /** Serialized script, used inside transaction inputs and outputs */