api: Drop sstable index caches on system/drop_sstable_caches

database.cc

@@ -1334,6 +1334,11 @@ database::drop_caches() const {
     for (auto&& e : tables) {
         table& t = *e.second;
         co_await t.get_row_cache().invalidate(row_cache::external_updater([] {}));
+
+        auto sstables = t.get_sstables();
+        for (sstables::shared_sstable sst : *sstables) {
+            co_await sst->drop_caches();
+        }
     }
     co_return;
 }

sstables/sstables.cc

@@ -1396,6 +1396,12 @@ future<> sstable::create_data() noexcept {
     });
 }
 
+future<> sstable::drop_caches() {
+    return _cached_index_file->evict_gently().then([this] {
+        return _index_cache->evict_gently();
+    });
+}
+
 future<> sstable::read_filter(const io_priority_class& pc) {
     if (!has_component(component_type::Filter)) {
         _components->filter = std::make_unique<utils::filter::always_present_filter>();

sstables/sstables.hh

@@ -815,6 +815,9 @@ public:
         return _origin;
     }
 
+    // Drops all evictable in-memory caches of on-disk content.
+    future<> drop_caches();
+
     // Allow the test cases from sstable_test.cc to test private methods. We use
     // a placeholder to avoid cluttering this class too much. The sstable_test class
     // will then re-export as public every method it needs.