Add cron to recalculate dbsize

kvrocks.conf

@@ -519,6 +519,13 @@ compaction-checker-range 0-7
 # e.g. bgsave-cron 0 3 * * * 0 4 * * *
 # would bgsave the db at 3am and 4am every day
 
+# Kvrocks doesn't store the key number directly. It needs to scan the DB and
+# then retrieve the key number by using the dbsize scan command.
+# The Dbsize scan scheduler auto-recalculates the estimated keys at scheduled time.
+# Time expression format is the same as crontab (currently only support * and int)
+# e.g. dbsize-scan-cron 0 * * * *
+# would recalculate the keyspace infos of the db every hour.
+
 # Command renaming.
 #
 # It is possible to change the name of dangerous commands in a shared

src/config/config.cc

@@ -137,6 +137,7 @@ Config::Config() {
       {"slaveof", true, new StringField(&slaveof_, "")},
       {"compact-cron", false, new StringField(&compact_cron_str_, "")},
       {"bgsave-cron", false, new StringField(&bgsave_cron_str_, "")},
+      {"dbsize-scan-cron", false, new StringField(&dbsize_scan_cron_str_, "")},
       {"replica-announce-ip", false, new StringField(&replica_announce_ip, "")},
       {"replica-announce-port", false, new UInt32Field(&replica_announce_port, 0, 0, PORT_LIMIT)},
       {"compaction-checker-range", false, new StringField(&compaction_checker_range_str_, "")},
@@ -292,6 +293,11 @@ void Config::initFieldValidator() {
          std::vector<std::string> args = util::Split(v, " \t");
          return bgsave_cron.SetScheduleTime(args);
        }},
+      {"dbsize-scan-cron",
+       [this](const std::string &k, const std::string &v) -> Status {
+         std::vector<std::string> args = util::Split(v, " \t");
+         return dbsize_scan_cron.SetScheduleTime(args);
+       }},
       {"compaction-checker-range",
        [this](const std::string &k, const std::string &v) -> Status {
          if (v.empty()) {

src/config/config.h

@@ -137,6 +137,7 @@ struct Config {
   uint32_t master_port = 0;
   Cron compact_cron;
   Cron bgsave_cron;
+  Cron dbsize_scan_cron;
   CompactionCheckerRange compaction_checker_range{-1, -1};
   int64_t force_compact_file_age;
   int force_compact_file_min_deleted_percentage;
@@ -246,6 +247,7 @@ struct Config {
   std::string slaveof_;
   std::string compact_cron_str_;
   std::string bgsave_cron_str_;
+  std::string dbsize_scan_cron_str_;
   std::string compaction_checker_range_str_;
   std::string profiling_sample_commands_str_;
   std::map<std::string, std::unique_ptr<ConfigField>> fields_;

src/server/server.cc

@@ -755,6 +755,23 @@ void Server::cron() {
         Status s = AsyncBgSaveDB();
         LOG(INFO) << "[server] Schedule to bgsave the db, result: " << s.Msg();
       }
+      if (config_->dbsize_scan_cron.IsEnabled() && config_->dbsize_scan_cron.IsTimeMatch(&now)) {
+        std::vector<std::string> namespaces;
+
+        auto tokens = namespace_.List();
+        for (auto &token : tokens) {
+          namespaces.emplace_back(token.second); // namespace
+        }
+
+        // add default namespace as fallback
+        namespaces.emplace_back(kDefaultNamespace);
+
+        for (auto &ns : namespaces) {
+          Status s = AsyncScanDBSize(ns);
+          LOG(INFO) << "[server] Schedule to recalculate the db size on namespace: " << ns << ", result: " << s.Msg();
+        }
+
+      }
     }
     // check every 10s
     if (counter != 0 && counter % 100 == 0) {

tests/cppunit/config_test.cc

@@ -46,6 +46,7 @@ TEST(Config, GetAndSet) {
       {"masterauth", "mytest_masterauth"},
       {"compact-cron", "1 2 3 4 5"},
       {"bgsave-cron", "5 4 3 2 1"},
+      {"dbsize-scan-cron", "1 2 3 2 1"},
       {"max-io-mb", "5000"},
       {"max-db-size", "6000"},
       {"max-replication-mb", "7000"},