From 369164318a5e0c952f3de426a68c48078c64c60c Mon Sep 17 00:00:00 2001
From: Mathias Stearn <mathias@10gen.com>
Date: Fri, 4 Sep 2015 19:28:39 -0400
Subject: SERVER-20300 Optimize StringMap

Major changes:
* Use 32-bit murmur3 rather than 128-bit
* Use bit-masks rather than modulus
* Default-constructed StringMaps don't allocate memory
* Can no longer configure max probe ratio or default starting size
---
 src/mongo/util/string_map.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

(limited to 'src/mongo/util/string_map.h')

diff --git a/src/mongo/util/string_map.h b/src/mongo/util/string_map.h
index 13e93977fcc..ff2946a8f95 100644
--- a/src/mongo/util/string_map.h
+++ b/src/mongo/util/string_map.h
@@ -29,12 +29,20 @@
 
 #pragma once
 
+#include <third_party/murmurhash3/MurmurHash3.h>
+
 #include "mongo/base/string_data.h"
 #include "mongo/util/unordered_fast_key_table.h"
 
 namespace mongo {
 
-typedef StringData::Hasher StringMapDefaultHash;
+struct StringMapDefaultHash {
+    uint32_t operator()(StringData a) const {
+        uint32_t hash;
+        MurmurHash3_x86_32(a.rawData(), a.size(), 0, &hash);
+        return hash;
+    }
+};
 
 struct StringMapDefaultEqual {
     bool operator()(StringData a, StringData b) const {
-- 
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