Rotate ledger headers if needed in SearchableBucketListSnapshot::getL…

…edgerHeader

src/bucket/BucketListSnapshot.cpp

@@ -127,6 +127,14 @@ SearchableBucketListSnapshot::getLedgerSeq() const
     return mSnapshot->getLedgerSeq();
 }
 
+LedgerHeader const&
+SearchableBucketListSnapshot::getLedgerHeader()
+{
+    releaseAssert(mSnapshot);
+    mSnapshotManager.maybeUpdateSnapshot(mSnapshot, mHistoricalSnapshots);
+    return mSnapshot->getLedgerHeader();
+}
+
 EvictionResult
 SearchableBucketListSnapshot::scanForEviction(
     uint32_t ledgerSeq, EvictionCounters& counters,

src/bucket/BucketListSnapshot.h

@@ -102,10 +102,6 @@ class SearchableBucketListSnapshot : public NonMovableOrCopyable
                                    std::shared_ptr<EvictionStatistics> stats,
                                    StateArchivalSettings const& sas);
     uint32_t getLedgerSeq() const;
-    LedgerHeader const&
-    getLedgerHeader() const
-    {
-        return mSnapshot->getLedgerHeader();
-    }
+    LedgerHeader const& getLedgerHeader();
 };
 }

src/ledger/LedgerStateSnapshot.h

@@ -130,6 +130,10 @@ class BucketSnapshotState : public AbstractLedgerStateSnapshot
 // A helper class to create and query read-only snapshots
 // Automatically decides whether to create a BucketList (recommended), or SQL
 // snapshot (deprecated, but currently supported)
+// NOTE: LedgerSnapshot is meant to be short-lived, and should not be persisted
+// across _different_ ledgers, as the state under the hood might change. Users
+// are expected to construct a new LedgerSnapshot each time they want to query
+// ledger state.
 class LedgerSnapshot : public NonMovableOrCopyable
 {
     std::unique_ptr<AbstractLedgerStateSnapshot const> mGetter;