fix: ScanQuorums should not start cache population for outdated quoru…

…ms (dashpay#5784)

## Issue being fixed or feature implemented
Cache population for old quorums is a cpu heavy operation and should be
avoided for inactive quorums _at least_ oin `ScanQuorums`. This issue is
critical for testnet and other small network because every mn
participate in almost every platform quorum and cache population for 2
months of quorums can easily block everything for 15+ minutes on a 4 cpu
node. On mainnet quorum distribution is much better but it's still a
small waste of cpu (or not so small for unlucky nodes).

dashpay#5761 follow-up

## What was done?
Do not start cache population for outdated quorums, improve logs in
`StartCachePopulatorThread` to make it easier to see what's going on.

## How Has This Been Tested?
run a mn on testnet

## Breaking Changes
n/a

## Checklist:
- [x] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have added or updated relevant unit/integration/functional/e2e
tests
- [ ] I have made corresponding changes to the documentation
- [x] I have assigned this pull request to a milestone _(for repository
code-owners and collaborators only)_

src/llmq/quorums.cpp

@@ -362,7 +362,7 @@ void CQuorumManager::CheckQuorumConnections(const Consensus::LLMQParams& llmqPar
     }
 }
 
-CQuorumPtr CQuorumManager::BuildQuorumFromCommitment(const Consensus::LLMQType llmqType, gsl::not_null<const CBlockIndex*> pQuorumBaseBlockIndex) const
+CQuorumPtr CQuorumManager::BuildQuorumFromCommitment(const Consensus::LLMQType llmqType, gsl::not_null<const CBlockIndex*> pQuorumBaseBlockIndex, bool populate_cache) const
 {
     const uint256& quorumHash{pQuorumBaseBlockIndex->GetBlockHash()};
     uint256 minedBlockHash;
@@ -392,7 +392,7 @@ CQuorumPtr CQuorumManager::BuildQuorumFromCommitment(const Consensus::LLMQType l
         }
     }
 
-    if (hasValidVvec) {
+    if (hasValidVvec && populate_cache) {
         // pre-populate caches in the background
         // recovering public key shares is quite expensive and would result in serious lags for the first few signing
         // sessions if the shares would be calculated on-demand
@@ -572,7 +572,9 @@ std::vector<CQuorumCPtr> CQuorumManager::ScanQuorums(Consensus::LLMQType llmqTyp
 
     for (auto& pQuorumBaseBlockIndex : pQuorumBaseBlockIndexes) {
         assert(pQuorumBaseBlockIndex);
-        auto quorum = GetQuorum(llmqType, pQuorumBaseBlockIndex);
+        // populate cache for keepOldConnections most recent quorums only
+        bool populate_cache = vecResultQuorums.size() < llmq_params_opt->keepOldConnections;
+        auto quorum = GetQuorum(llmqType, pQuorumBaseBlockIndex, populate_cache);
         assert(quorum != nullptr);
         vecResultQuorums.emplace_back(quorum);
     }
@@ -602,7 +604,7 @@ CQuorumCPtr CQuorumManager::GetQuorum(Consensus::LLMQType llmqType, const uint25
     return GetQuorum(llmqType, pQuorumBaseBlockIndex);
 }
 
-CQuorumCPtr CQuorumManager::GetQuorum(Consensus::LLMQType llmqType, gsl::not_null<const CBlockIndex*> pQuorumBaseBlockIndex) const
+CQuorumCPtr CQuorumManager::GetQuorum(Consensus::LLMQType llmqType, gsl::not_null<const CBlockIndex*> pQuorumBaseBlockIndex, bool populate_cache) const
 {
     auto quorumHash = pQuorumBaseBlockIndex->GetBlockHash();
 
@@ -617,7 +619,7 @@ CQuorumCPtr CQuorumManager::GetQuorum(Consensus::LLMQType llmqType, gsl::not_nul
         return pQuorum;
     }
 
-    return BuildQuorumFromCommitment(llmqType, pQuorumBaseBlockIndex);
+    return BuildQuorumFromCommitment(llmqType, pQuorumBaseBlockIndex, populate_cache);
 }
 
 size_t CQuorumManager::GetQuorumRecoveryStartOffset(const CQuorumCPtr pQuorum, const CBlockIndex* pIndex) const
@@ -850,7 +852,10 @@ void CQuorumManager::StartCachePopulatorThread(const CQuorumCPtr pQuorum) const
     }
 
     cxxtimer::Timer t(true);
-    LogPrint(BCLog::LLMQ, "CQuorumManager::StartCachePopulatorThread -- start\n");
+    LogPrint(BCLog::LLMQ, "CQuorumManager::StartCachePopulatorThread -- type=%d height=%d hash=%s start\n",
+            ToUnderlying(pQuorum->params.type),
+            pQuorum->m_quorum_base_block_index->nHeight,
+            pQuorum->m_quorum_base_block_index->GetBlockHash().ToString());
 
     // when then later some other thread tries to get keys, it will be much faster
     workerPool.push([pQuorum, t, this](int threadId) {
@@ -862,7 +867,11 @@ void CQuorumManager::StartCachePopulatorThread(const CQuorumCPtr pQuorum) const
                 pQuorum->GetPubKeyShare(i);
             }
         }
-        LogPrint(BCLog::LLMQ, "CQuorumManager::StartCachePopulatorThread -- done. time=%d\n", t.count());
+        LogPrint(BCLog::LLMQ, "CQuorumManager::StartCachePopulatorThread -- type=%d height=%d hash=%s done. time=%d\n",
+                ToUnderlying(pQuorum->params.type),
+                pQuorum->m_quorum_base_block_index->nHeight,
+                pQuorum->m_quorum_base_block_index->GetBlockHash().ToString(),
+                t.count());
     });
 }
 

src/llmq/quorums.h

@@ -267,10 +267,10 @@ class CQuorumManager
     // all private methods here are cs_main-free
     void CheckQuorumConnections(const Consensus::LLMQParams& llmqParams, const CBlockIndex *pindexNew) const;
 
-    CQuorumPtr BuildQuorumFromCommitment(Consensus::LLMQType llmqType, gsl::not_null<const CBlockIndex*> pQuorumBaseBlockIndex) const;
+    CQuorumPtr BuildQuorumFromCommitment(Consensus::LLMQType llmqType, gsl::not_null<const CBlockIndex*> pQuorumBaseBlockIndex, bool populate_cache) const;
     bool BuildQuorumContributions(const CFinalCommitmentPtr& fqc, const std::shared_ptr<CQuorum>& quorum) const;
 
-    CQuorumCPtr GetQuorum(Consensus::LLMQType llmqType, gsl::not_null<const CBlockIndex*> pindex) const;
+    CQuorumCPtr GetQuorum(Consensus::LLMQType llmqType, gsl::not_null<const CBlockIndex*> pindex, bool populate_cache = true) const;
     /// Returns the start offset for the masternode with the given proTxHash. This offset is applied when picking data recovery members of a quorum's
     /// memberlist and is calculated based on a list of all member of all active quorums for the given llmqType in a way that each member
     /// should receive the same number of request if all active llmqType members requests data from one llmqType quorum.