phet commented on code in PR #3700: URL: https://github.com/apache/gobblin/pull/3700#discussion_r1222561966
########## gobblin-runtime/src/main/java/org/apache/gobblin/runtime/api/MySQLMultiActiveLeaseArbiter.java: ########## @@ -0,0 +1,389 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.gobblin.runtime.api; + +import java.io.IOException; +import java.sql.Connection; +import java.sql.PreparedStatement; +import java.sql.ResultSet; +import java.sql.SQLException; +import java.sql.Timestamp; + +import com.google.inject.Inject; +import com.typesafe.config.Config; +import com.zaxxer.hikari.HikariDataSource; + +import javax.sql.DataSource; + +import org.apache.gobblin.broker.SharedResourcesBrokerFactory; +import org.apache.gobblin.configuration.ConfigurationKeys; +import org.apache.gobblin.metastore.MysqlDataSourceFactory; +import org.apache.gobblin.service.ServiceConfigKeys; +import org.apache.gobblin.util.ConfigUtils; + + +/** + * MySQL based implementation of the {@link MultiActiveLeaseArbiter} which uses a MySQL store to resolve ownership of + * a flow event amongst multiple competing instances. A MySQL table is used to store flow identifying information as + * well as the flow action associated with it. It uses two additional values of the `event_timestamp` and + * `lease_acquisition_timestamp` to indicate an active lease, expired lease, and state of no longer leasing. The table + * schema is as follows: + * [flow_group | flow_name | flow_execution_id | flow_action | event_timestamp | lease_acquisition_timestamp] + * (----------------------primary key------------------------) + * We also maintain another table in the database with two constants that allow us to coordinate between instances and + * ensure they are using the same values to base their coordination off of. + * [epsilon | linger] + * `epsilon` - time within we consider to timestamps to be the same, to account for between-host clock drift + * `linger` - minimum time to occur before another host may attempt a lease on a flow event. It should be much greater + * than epsilon and encapsulate executor communication latency including retry attempts + * + * The `event_timestamp` is the time of the flow_action event request. + * ---Event consolidation--- + * Note that for the sake of simplification, we only allow one event associated with a particular flow's flow_action + * (ie: only one LAUNCH for example of flow FOO, but there can be a LAUNCH, KILL, & RESUME for flow FOO at once) during + * the time it takes to execute the flow action. In most cases, the execution time should be so negligible that this + * event consolidation of duplicate flow action requests is not noticed and even during executor downtime this behavior + * is acceptable as the user generally expects a timely execution of the most recent request rather than one execution + * per request. + * + * The `lease_acquisition_timestamp` is the time a host acquired ownership of this flow action, and it is valid for + * `linger` period of time after which it expires and any host can re-attempt ownership. In most cases, the original + * host should actually complete its work while having the lease and then mark the flow action as NULL to indicate no + * further leasing should be done for the event. + */ +public class MySQLMultiActiveLeaseArbiter implements MultiActiveLeaseArbiter { + /** `j.u.Function` variant for an operation that may @throw IOException or SQLException: preserves method signature checked exceptions */ + @FunctionalInterface + protected interface CheckedFunction<T, R> { + R apply(T t) throws IOException, SQLException; + } + + public static final String CONFIG_PREFIX = "MySQLMultiActiveLeaseArbiter"; + + protected final DataSource dataSource; + private final String leaseArbiterTableName; + private final String constantsTableName; + private final int epsilon; + private final int linger; + protected static final String WHERE_CLAUSE_TO_MATCH_KEY = "WHERE flow_group=? AND flow_name=? AND flow_execution_id=?" + + " AND flow_action=?"; + protected static final String WHERE_CLAUSE_TO_MATCH_ROW = "WHERE flow_group=? AND flow_name=? AND flow_execution_id=?" + + " AND flow_action=? AND event_timestamp=? AND lease_acquisition_timestamp=?"; + + protected static final String SELECT_AFTER_INSERT_STATEMENT = "SELECT ROW_COUNT() AS rows_inserted_count, " + + "lease_acquisition_timestamp, linger FROM %s, %s " + WHERE_CLAUSE_TO_MATCH_KEY; + + // Does a cross join between the two tables to have epsilon and linger values available. Returns the following values: + // event_timestamp, lease_acquisition_timestamp, isWithinEpsilon (boolean if event_timestamp in table is within + // epsilon), leaseValidityStatus (1 if lease has not expired, 2 if expired, 3 if column is NULL or no longer leasing) + protected static final String GET_EVENT_INFO_STATEMENT = "SELECT event_timestamp, lease_acquisition_timestamp, " + + "abs(event_timestamp - ?) <= epsilon as isWithinEpsilon, CASE " + + "WHEN CURRENT_TIMESTAMP < (lease_acquisition_timestamp + linger) then 1" + + "WHEN CURRENT_TIMESTAMP >= (lease_acquisition_timestamp + linger) then 2" + + "ELSE 3 END as leaseValidityStatus, linger FROM %s, %s " + WHERE_CLAUSE_TO_MATCH_KEY; + + // Insert or update row to acquire lease if values have not changed since the previous read + // Need to define three separate statements to handle cases where row does not exist or has null values to check + protected static final String CONDITIONALLY_ACQUIRE_LEASE_IF_NEW_ROW_STATEMENT = "INSERT INTO %s " + + "(flow_group, flow_name, flow_execution_id, flow_action, event_timestamp) VALUES (?, ?, ?, ?, ?) WHERE NOT " + + "EXISTS (SELECT * FROM %s " + WHERE_CLAUSE_TO_MATCH_KEY + "); " + SELECT_AFTER_INSERT_STATEMENT; + protected static final String CONDITIONALLY_ACQUIRE_LEASE_IF_FINISHED_LEASING_STATEMENT = "UPDATE %s " + + "SET event_timestamp=?" + WHERE_CLAUSE_TO_MATCH_KEY + + " AND event_timestamp=? AND lease_acquisition_timestamp is NULL; " + SELECT_AFTER_INSERT_STATEMENT; + protected static final String CONDITIONALLY_ACQUIRE_LEASE_IF_MATCHING_ALL_COLS_STATEMENT = "UPDATE %s " + + "SET event_timestamp=?" + WHERE_CLAUSE_TO_MATCH_ROW + + " AND event_timestamp=? AND lease_acquisition_timestamp=?; " + SELECT_AFTER_INSERT_STATEMENT; + + // Complete lease acquisition if values have not changed since lease was acquired + protected static final String CONDITIONALLY_COMPLETE_LEASE_STATEMENT = "UPDATE %s SET " + + "lease_acquisition_timestamp = NULL " + WHERE_CLAUSE_TO_MATCH_ROW; + + // TODO: define retention on this table + private static final String CREATE_LEASE_ARBITER_TABLE_STATEMENT = "CREATE TABLE IF NOT EXISTS %S (" + + "flow_group varchar(" + ServiceConfigKeys.MAX_FLOW_GROUP_LENGTH + ") NOT NULL, flow_name varchar(" + + ServiceConfigKeys.MAX_FLOW_GROUP_LENGTH + ") NOT NULL, " + "flow_execution_id varchar(" + + ServiceConfigKeys.MAX_FLOW_EXECUTION_ID_LENGTH + ") NOT NULL, flow_action varchar(100) NOT NULL, " + + "event_timestamp TIMESTAMP DEFAULT CURRENT_TIMESTAMP, " + + "lease_acquisition_timestamp TIMESTAMP DEFAULT CURRENT_TIMESTAMP," + + "PRIMARY KEY (flow_group,flow_name,flow_execution_id,flow_action))"; + + private static final String CREATE_CONSTANTS_TABLE_STATEMENT = "CREATE TABLE IF NOT EXISTS %s " + + "(epsilon INT, linger INT), PRIMARY KEY (epsilon, linger); INSERT INTO %s (epsilon, linger) VALUES (?,?)"; + + @Inject + public MySQLMultiActiveLeaseArbiter(Config config) throws IOException { + if (config.hasPath(CONFIG_PREFIX)) { + config = config.getConfig(CONFIG_PREFIX).withFallback(config); + } else { + throw new IOException("Please specify the config for MySQLMultiActiveLeaseArbiter"); Review Comment: minor: but I suggest inserting `CONFIG_PREFIX` into the error message, so there's no confusion there -- This is an automated message from the Apache Git Service. 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