Merge #16945: refactor: introduce CChainState::GetCoinsCacheSizeState

02b9511d6bace5711e454d2b685b2fee0d65e341 tests: add tests for GetCoinsCacheSizeState (James O'Beirne)
b17e91d842724d2888a179a73585cc4c2ef1dc21 refactoring: introduce CChainState::GetCoinsCacheSizeState (James O'Beirne)

Pull request description:

  This is part of the [assumeutxo project](https://github.com/bitcoin/bitcoin/projects/11):

  Parent PR: #15606
  Issue: #15605
  Specification: https://github.com/jamesob/assumeutxo-docs/tree/master/proposal

  ---

  This pulls out the routine for detection of how full the coins cache is from
  FlushStateToDisk. We use this logic independently when deciding when to flush
  the coins cache during UTXO snapshot activation ([see here](https://github.com/bitcoin/bitcoin/pull/15606/commits/231fb5f17e3bb8ce3323c559ef6f9b3aaa066543#diff-24efdb00bfbe56b140fb006b562cc70bR5275)).

ACKs for top commit:
  ariard:
    Code review ACK 02b9511.
  ryanofsky:
    Code review ACK 02b9511d6bace5711e454d2b685b2fee0d65e341. Just rebase, new COIN_SIZE comment, and new test message since last review

Tree-SHA512: 8bdd78bf68a4a5d33a776e73fcc2857f050d6d102caa4997ed19ca25468c1358e6e728199d61b423033c02e6bc8f00a1d9da52cf17a2d37d70860fca9237ea7c

1 files changed, 35 insertions, 6 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index cdffec48ab..755f8d43f9 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2187,13 +2187,44 @@ bool CChainState::ConnectBlock(const CBlock& block, BlockValidationState& state,
     return true;
 }
 
+CoinsCacheSizeState CChainState::GetCoinsCacheSizeState(const CTxMemPool& tx_pool)
+{
+    return this->GetCoinsCacheSizeState(
+        tx_pool,
+        nCoinCacheUsage,
+        gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000);
+}
+
+CoinsCacheSizeState CChainState::GetCoinsCacheSizeState(
+    const CTxMemPool& tx_pool,
+    size_t max_coins_cache_size_bytes,
+    size_t max_mempool_size_bytes)
+{
+    int64_t nMempoolUsage = tx_pool.DynamicMemoryUsage();
+    int64_t cacheSize = CoinsTip().DynamicMemoryUsage();
+    int64_t nTotalSpace =
+        max_coins_cache_size_bytes + std::max<int64_t>(max_mempool_size_bytes - nMempoolUsage, 0);
+
+    //! No need to periodic flush if at least this much space still available.
+    static constexpr int64_t MAX_BLOCK_COINSDB_USAGE_BYTES = 10 * 1024 * 1024;  // 10MB
+    int64_t large_threshold =
+        std::max((9 * nTotalSpace) / 10, nTotalSpace - MAX_BLOCK_COINSDB_USAGE_BYTES);
+
+    if (cacheSize > nTotalSpace) {
+        LogPrintf("Cache size (%s) exceeds total space (%s)\n", cacheSize, nTotalSpace);
+        return CoinsCacheSizeState::CRITICAL;
+    } else if (cacheSize > large_threshold) {
+        return CoinsCacheSizeState::LARGE;
+    }
+    return CoinsCacheSizeState::OK;
+}
+
 bool CChainState::FlushStateToDisk(
     const CChainParams& chainparams,
     BlockValidationState &state,
     FlushStateMode mode,
     int nManualPruneHeight)
 {
-    int64_t nMempoolUsage = mempool.DynamicMemoryUsage();
     LOCK(cs_main);
     assert(this->CanFlushToDisk());
     static int64_t nLastWrite = 0;
@@ -2208,6 +2239,7 @@ bool CChainState::FlushStateToDisk(
     {
         bool fFlushForPrune = false;
         bool fDoFullFlush = false;
+        CoinsCacheSizeState cache_state = GetCoinsCacheSizeState(::mempool);
         LOCK(cs_LastBlockFile);
         if (fPruneMode && (fCheckForPruning || nManualPruneHeight > 0) && !fReindex) {
             if (nManualPruneHeight > 0) {
@@ -2236,13 +2268,10 @@ bool CChainState::FlushStateToDisk(
         if (nLastFlush == 0) {
             nLastFlush = nNow;
         }
-        int64_t nMempoolSizeMax = gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000;
-        int64_t cacheSize = CoinsTip().DynamicMemoryUsage();
-        int64_t nTotalSpace = nCoinCacheUsage + std::max<int64_t>(nMempoolSizeMax - nMempoolUsage, 0);
         // The cache is large and we're within 10% and 10 MiB of the limit, but we have time now (not in the middle of a block processing).
-        bool fCacheLarge = mode == FlushStateMode::PERIODIC && cacheSize > std::max((9 * nTotalSpace) / 10, nTotalSpace - MAX_BLOCK_COINSDB_USAGE * 1024 * 1024);
+        bool fCacheLarge = mode == FlushStateMode::PERIODIC && cache_state >= CoinsCacheSizeState::LARGE;
         // The cache is over the limit, we have to write now.
-        bool fCacheCritical = mode == FlushStateMode::IF_NEEDED && cacheSize > nTotalSpace;
+        bool fCacheCritical = mode == FlushStateMode::IF_NEEDED && cache_state >= CoinsCacheSizeState::CRITICAL;
         // It's been a while since we wrote the block index to disk. Do this frequently, so we don't need to redownload after a crash.
         bool fPeriodicWrite = mode == FlushStateMode::PERIODIC && nNow > nLastWrite + (int64_t)DATABASE_WRITE_INTERVAL * 1000000;
         // It's been very long since we flushed the cache. Do this infrequently, to optimize cache usage.