skip removing entries from sqlite if store-queue-on-shutdown is used

if `--store-queue-on-shutdown` is used, database should only be accessed during
shutdown and on initial startup. Skipping the done() saves the unnecessary query
preparation, database locks, etc...

instead truncate queue database after successfully importing the retention database.

 - fixes #369

libgearman-server/plugins/base.h

@@ -147,6 +147,11 @@ class Context {
     _store_on_shutdown= store_on_shutdown_;
   }
 
+  bool is_store_on_shutdown()
+  {
+    return _store_on_shutdown;
+  }
+
   bool has_error()
   {
     return _error_string.size();

libgearman-server/plugins/queue/sqlite/instance.cc

@@ -432,6 +432,11 @@ gearmand_error_t Instance::done(gearman_server_st*,
                                    const char *function_name,
                                    size_t function_name_size)
 {
+  if (is_store_on_shutdown())
+  {
+    return GEARMAND_SUCCESS;
+  }
+
   gearmand_log_debug(GEARMAN_DEFAULT_LOG_PARAM,
                      "sqlite done: unique_key: %.*s, function_name: %.*s",
                      int(unique_size), (char*)unique,
@@ -593,6 +598,17 @@ gearmand_error_t Instance::replay_loop(gearman_server_st *server)
                                "failed to reset REPLAY prep statement: %s", sqlite3_errmsg(_db));
   }
 
+  /* truncate database now if in store_on_shutdown mode */
+  if (is_store_on_shutdown())
+  {
+    std::string query("DELETE FROM ");
+    query+= _table;
+    if (_sqlite_dispatch(query) == false) {
+      return gearmand_log_gerror(GEARMAN_DEFAULT_LOG_PARAM, GEARMAND_QUEUE_ERROR,
+                                 "failed to truncate table: %s", sqlite3_errmsg(_db));
+    }
+  }
+
   if (row_count == 0)
   {
     return GEARMAND_SUCCESS;
@@ -603,5 +619,3 @@ gearmand_error_t Instance::replay_loop(gearman_server_st *server)
 
 } // namespace queue
 } // namespace gearmand
-
-

libgearman-server/plugins/queue/sqlite/queue.cc

@@ -77,7 +77,7 @@ Sqlite::Sqlite() :
 {
   command_line_options().add_options()
     ("libsqlite3-db", boost::program_options::value(&schema), "Database file to use.")
-    ("store-queue-on-shutdown", boost::program_options::bool_switch(&_store_on_shutdown)->default_value(false), "Store queue on shutdown.")
+    ("store-queue-on-shutdown", boost::program_options::bool_switch(&_store_on_shutdown)->default_value(false), "Store queue on shutdown only.")
     ("libsqlite3-table", boost::program_options::value(&table)->default_value(GEARMAND_QUEUE_SQLITE_DEFAULT_TABLE), "Table to use.")
     ;
 }