Bump -dbcache default to 300MiB

Also cap the allocation for the leveldb-specific cache for the UTXO set
to 8MiB.
This avoids that the extra cache memory goes to the much less effective
leveldb cache instead of our application-level cache.

src/init.cpp

@@ -1224,10 +1224,10 @@ bool AppInit2(Config& config, boost::thread_group& threadGroup, CScheduler& sche
     nTotalCache = std::max(nTotalCache, nMinDbCache << 20); // total cache cannot be less than nMinDbCache
     nTotalCache = std::min(nTotalCache, nMaxDbCache << 20); // total cache cannot be greated than nMaxDbcache
     int64_t nBlockTreeDBCache = nTotalCache / 8;
-    if (nBlockTreeDBCache > (1 << 21) && !GetBoolArg("-txindex", DEFAULT_TXINDEX))
-        nBlockTreeDBCache = (1 << 21); // block tree db cache shouldn't be larger than 2 MiB
+    nBlockTreeDBCache = std::min(nBlockTreeDBCache, (GetBoolArg("-txindex", DEFAULT_TXINDEX) ? nMaxBlockDBAndTxIndexCache : nMaxBlockDBCache) << 20);
     nTotalCache -= nBlockTreeDBCache;
     int64_t nCoinDBCache = std::min(nTotalCache / 2, (nTotalCache / 4) + (1 << 23)); // use 25%-50% of the remainder for disk cache
+    nCoinDBCache = std::min(nCoinDBCache, nMaxCoinsDBCache << 20); // cap total coins db cache
     nTotalCache -= nCoinDBCache;
     nCoinCacheUsage = nTotalCache; // the rest goes to in-memory cache
     LogPrintf("Cache configuration:\n");