Avoid table does not exist errors if nested is unavailable

src/Databases/PostgreSQL/DatabasePostgreSQLReplica.cpp

@@ -88,6 +88,7 @@ void DatabasePostgreSQLReplica<Base>::startSynchronization()
                      : (global_context.getSettingsRef().max_insert_block_size.value),
             global_context.getMacros()->expand(settings->postgresql_tables_list.value));
 
+    /// TODO: may be no need to always fetch
     std::unordered_set<std::string> tables_to_replicate = replication_handler->fetchRequiredTables(connection->conn());
 
     for (const auto & table_name : tables_to_replicate)
@@ -160,7 +161,9 @@ StoragePtr DatabasePostgreSQLReplica<Base>::tryGetTable(const String & name, con
     }
 
     auto table = tables.find(name);
-    if (table != tables.end() && table->second->as<StoragePostgreSQLReplica>()->isNestedLoaded())
+    /// Here it is possible that nested table is temporarily out of reach, but return storage anyway,
+    /// it will not allow to read if nested is unavailable at the moment
+    if (table != tables.end())
         return table->second;
 
     return StoragePtr{};

src/Databases/PostgreSQL/DatabasePostgreSQLReplica.h

@@ -58,7 +58,6 @@ public:
 
     void shutdown() override;
 
-
 private:
     void startSynchronization();
 

src/Storages/PostgreSQL/StoragePostgreSQLReplica.cpp

@@ -352,6 +352,7 @@ void StoragePostgreSQLReplica::dropNested()
     interpreter.execute();
 
     nested_storage = nullptr;
+    LOG_WARNING(&Poco::Logger::get("StoragePostgreSQLReplica"), "Dropped (or temporarily) nested table {}", getNestedTableName());
 }
 
 
@@ -373,24 +374,19 @@ Pipe StoragePostgreSQLReplica::read(
         size_t max_block_size,
         unsigned num_streams)
 {
-    /// If initial table sync has not yet finished, nested tables might not be created yet.
-    /// Or nested table might be attempted to get dropped. (Second mutex lock in dropNested()).
+    /// TODO: are there other places where this lock is needed
     std::unique_lock lock(nested_mutex, std::defer_lock);
-    if (!nested_loaded || !lock.try_lock())
-    {
-        LOG_WARNING(&Poco::Logger::get("StoragePostgreSQLReplica"), "Table {} is not loaded yet", getNestedTableName());
-        return Pipe();
-    }
 
-    /// Should throw if there is no nested storage
+    if (nested_loaded && lock.try_lock())
+    {
         if (!nested_storage)
             getNested();
 
         auto storage_lock = nested_storage->lockForShare(context.getCurrentQueryId(), context.getSettingsRef().lock_acquire_timeout);
 
         const StorageMetadataPtr & nested_metadata = nested_storage->getInMemoryMetadataPtr();
-
         Block nested_header = nested_metadata->getSampleBlock();
+
         ColumnWithTypeAndName & sign_column = nested_header.getByPosition(nested_header.columns() - 2);
         ColumnWithTypeAndName & version_column = nested_header.getByPosition(nested_header.columns() - 1);
 
@@ -446,6 +442,10 @@ Pipe StoragePostgreSQLReplica::read(
         }
 
         return pipe;
+    }
+
+    LOG_WARNING(&Poco::Logger::get("StoragePostgreSQLReplica"), "Nested table {} is unavailable or is not loaded yet", getNestedTableName());
+    return Pipe();
 }
 
 

tests/integration/test_postgresql_replica_database_engine/test.py

@@ -316,14 +316,12 @@ def test_table_schema_changes(started_cluster):
         check_tables_are_synchronized('postgresql_replica_{}'.format(i));
 
     expected = instance.query("SELECT key, value1, value3 FROM test_database.postgresql_replica_3 ORDER BY key");
-    cursor.execute("ALTER TABLE postgresql_replica_4 DROP COLUMN value2")
+    cursor.execute("ALTER TABLE postgresql_replica_{} DROP COLUMN value2".format(random.randint(0, 4)))
 
     for i in range(NUM_TABLES):
         cursor.execute("INSERT INTO postgresql_replica_{} VALUES (50, {}, {})".format(i, i, i))
         cursor.execute("UPDATE postgresql_replica_{} SET value3 = 12 WHERE key%2=0".format(i))
 
-    time.sleep(4)
-    print("Sync check")
     for i in range(NUM_TABLES):
         check_tables_are_synchronized('postgresql_replica_{}'.format(i));