Add an option to enable/disable auto flush for specific DB (#183)

* User can disable auto flush by background thread selectively.

include/libjungle/db_config.h

@@ -104,6 +104,7 @@ class DBConfig {
     DBConfig()
         : allowOverwriteSeqNum(false)
         , logSectionOnly(false)
+        , autoLogFlush(true)
         , truncateInconsecutiveLogs(true)
         , logFileTtl_sec(0)
         , maxKeepingMemtables(0)
@@ -179,11 +180,21 @@ class DBConfig {
      */
     bool allowOverwriteSeqNum;
 
-    /*
+    /**
      * Disable table section and use logging part only.
      */
     bool logSectionOnly;
 
+    /**
+     * If it is normal DB instance (`readOnly = false` and `logSectionOnly = false`),
+     * background flusher thread will automatically flush logs to L0 tables.
+     *
+     * WARNING:
+     *   If it is set to `false`, users should manually call `flushLogs()`.
+     *   The more unflushed logs, the more memory consumption.
+     */
+    bool autoLogFlush;
+
     /*
      * (Only when `logSectionOnly == true`)
      * Truncate tail logs if they are inconsecutive,

src/log_mgr.cc

@@ -1884,18 +1884,19 @@ Status LogMgr::getLastSyncedSeqNum(uint64_t& seq_num_out) {
     return Status();
 }
 
-
 bool LogMgr::checkTimeToFlush(const GlobalConfig& config) {
     Status s;
     uint64_t l_last_flush = 0;
     uint64_t l_max = 0;
     uint64_t seq_last_flush = NOT_INITIALIZED;
     uint64_t seq_max = NOT_INITIALIZED;
 
-    if (getDbConfig()->readOnly) return false;
+    const DBConfig* db_config = getDbConfig();
+    if (db_config->readOnly) return false;
     if (syncSema.grabbed) return false;
     if (flushSema.grabbed) return false;
-    if (getDbConfig()->logSectionOnly) return false;
+    if (db_config->logSectionOnly) return false;
+    if (!db_config->autoLogFlush) return false;
 
     const size_t MAX_TRY = 10;
     size_t num_try = 0;

tests/jungle/basic_op_test.cc

@@ -3114,6 +3114,57 @@ int serialized_sync_and_flush_test() {
     return 0;
 }
 
+int disabling_auto_flush_test() {
+    std::string filename;
+    TEST_SUITE_PREPARE_PATH(filename);
+
+    jungle::Status s;
+    jungle::DBConfig config;
+    TEST_CUSTOM_DB_CONFIG(config);
+    jungle::DB* db1 = nullptr;
+    jungle::DB* db2 = nullptr;
+
+    jungle::GlobalConfig g_config;
+    g_config.numFlusherThreads = 1;
+    g_config.flusherMinRecordsToTrigger = 100;
+    jungle::init(g_config);
+
+    config.maxEntriesInLogFile = 100;
+    std::string db1_file = filename + "_db1";
+    CHK_Z(jungle::DB::open(&db1, db1_file, config));
+
+    config.autoLogFlush = false;
+    std::string db2_file = filename + "_db2";
+    CHK_Z(jungle::DB::open(&db2, db2_file, config));
+
+    auto insert_keys = [&](size_t from, size_t to) {
+        for (size_t ii = from; ii < to; ++ii) {
+            std::string key_str = "key" + TestSuite::lzStr(5, ii);
+            std::string val_str = "val" + TestSuite::lzStr(5, ii);
+            CHK_Z( db1->set( jungle::KV(key_str, val_str) ) );
+            CHK_Z( db2->set( jungle::KV(key_str, val_str) ) );
+        }
+        return 0;
+    };
+
+    CHK_Z( insert_keys(0, 200) );
+
+    // Wait longer than flusher sleep time.
+    TestSuite::sleep_ms(g_config.flusherSleepDuration_ms * 2, "wait for flusher..");
+
+    uint64_t db1_flushed_seqnum = 0, db2_flushed_seqnum = 0;
+    CHK_Z(db1->getLastFlushedSeqNum(db1_flushed_seqnum));
+    CHK_EQ(jungle::Status::INVALID_SEQNUM,
+           db2->getLastFlushedSeqNum(db2_flushed_seqnum).getValue());
+
+    CHK_Z(jungle::DB::close(db1));
+    CHK_Z(jungle::DB::close(db2));
+    CHK_Z(jungle::shutdown());
+
+    TEST_SUITE_CLEANUP_PATH();
+    return 0;
+}
+
 int main(int argc, char** argv) {
     TestSuite ts(argc, argv);
 
@@ -3169,6 +3220,7 @@ int main(int argc, char** argv) {
     ts.doTest("sample key test", sample_key_test);
     ts.doTest("log flush add new file race test", log_flush_add_new_file_race_test);
     ts.doTest("serialized sync and flush test", serialized_sync_and_flush_test);
+    ts.doTest("disabling auto flush test", disabling_auto_flush_test);
 
     return 0;
 }

tests/jungle/log_reclaim_test.cc

@@ -1660,7 +1660,6 @@ int dedicated_flusher_test() {
     return 0;
 }
 
-
 } using namespace log_reclaim_test;
 
 int main(int argc, char** argv) {
@@ -1741,7 +1740,6 @@ int main(int argc, char** argv) {
     ts.doTest("snapshot on purged memtable test",
               snapshot_on_purged_memtable_test);
 
-
     ts.doTest("dedicated flusher test",
               dedicated_flusher_test);