phet commented on code in PR #3700: URL: https://github.com/apache/gobblin/pull/3700#discussion_r1222573977
########## 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; Review Comment: what about: ``` (lease_acquisition_timestamp + linger) < CURRENT_TIMESTAMP as isLeaseExpired ``` then you either have: 1 (TRUE) - expired 0 (FALSE) - not expired NULL - no lease (IMO easier to follow than SQL `CASE`) -- This is an automated message from the Apache Git Service. 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