aboutsummaryrefslogtreecommitdiff
path: root/src/coins.h
diff options
context:
space:
mode:
Diffstat (limited to 'src/coins.h')
-rw-r--r--src/coins.h10
1 files changed, 9 insertions, 1 deletions
diff --git a/src/coins.h b/src/coins.h
index dca1beabb6..d8135e0d9a 100644
--- a/src/coins.h
+++ b/src/coins.h
@@ -95,8 +95,16 @@ public:
* This *must* return size_t. With Boost 1.46 on 32-bit systems the
* unordered_map will behave unpredictably if the custom hasher returns a
* uint64_t, resulting in failures when syncing the chain (#4634).
+ *
+ * Having the hash noexcept allows libstdc++'s unordered_map to recalculate
+ * the hash during rehash, so it does not have to cache the value. This
+ * reduces node's memory by sizeof(size_t). The required recalculation has
+ * a slight performance penalty (around 1.6%), but this is compensated by
+ * memory savings of about 9% which allow for a larger dbcache setting.
+ *
+ * @see https://gcc.gnu.org/onlinedocs/gcc-9.2.0/libstdc++/manual/manual/unordered_associative.html
*/
- size_t operator()(const COutPoint& id) const {
+ size_t operator()(const COutPoint& id) const noexcept {
return SipHashUint256Extra(k0, k1, id.hash, id.n);
}
};