init: Correct coins db cache size setting

The chainstate caches are currently re-balanced on startup
even in the non-assumeutxo case, leading to the database being
needlessly re-opened and its cache re-allocated.

Similar to `InitCoinsCache` and `m_coinstip_cache_size_bytes` the
`m_coinsdb_cache_size_bytes` should be set in `InitCoinsDB`.

Together with only conservatively setting the cache values when a
assumeutxo chainstate is present, this allows for skipping the cache
re-balance during initialization in the normal non-assumeutxo case.

Author: TheCharlatan

src/node/chainstate.cpp

@@ -95,11 +95,12 @@ static ChainstateLoadResult CompleteChainstateInitialization(
     assert(chainman.m_total_coinstip_cache > 0);
     assert(chainman.m_total_coinsdb_cache > 0);
 
-    // Conservative value which is arbitrarily chosen, as it will ultimately be changed
-    // by a call to `chainman.MaybeRebalanceCaches()`. We just need to make sure
-    // that the sum of the two caches (40%) does not exceed the allowable amount
-    // during this temporary initialization state.
-    double init_cache_fraction = 0.2;
+    // If running with multiple chainstates, limit the cache sizes with a
+    // discount factor. If discounted the actual cache size will be
+    // recalculated by `chainman.MaybeRebalanceCaches()`. The discount factor
+    // is conservatively chosen such that the sum of the caches does not exceed
+    // the allowable amount during this temporary initialization state.
+    double init_cache_fraction = chainman.GetAll().size() > 1 ? 0.2 : 1.0;
 
     // At this point we're either in reindex or we've loaded a useful
     // block tree into BlockIndex()!

src/validation.cpp

@@ -1972,6 +1972,8 @@ void Chainstate::InitCoinsDB(
             .obfuscate = true,
             .options = m_chainman.m_options.coins_db},
         m_chainman.m_options.coins_view);
+
+    m_coinsdb_cache_size_bytes = cache_size_bytes;
 }
 
 void Chainstate::InitCoinsCache(size_t cache_size_bytes)