dcapwell commented on code in PR #3574: URL: https://github.com/apache/cassandra/pull/3574#discussion_r1778813778
########## src/java/org/apache/cassandra/tcm/sequences/DropAccordTable.java: ########## @@ -0,0 +1,364 @@ +/* + * 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.cassandra.tcm.sequences; + +import java.io.IOException; +import java.time.Duration; +import java.util.Objects; +import java.util.concurrent.ExecutionException; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import org.apache.cassandra.cql3.ColumnIdentifier; +import org.apache.cassandra.db.TypeSizes; +import org.apache.cassandra.io.util.DataInputPlus; +import org.apache.cassandra.io.util.DataOutputPlus; +import org.apache.cassandra.schema.Keyspaces; +import org.apache.cassandra.schema.TableId; +import org.apache.cassandra.schema.TableMetadata; +import org.apache.cassandra.service.accord.AccordService; +import org.apache.cassandra.tcm.ClusterMetadata; +import org.apache.cassandra.tcm.ClusterMetadataService; +import org.apache.cassandra.tcm.Epoch; +import org.apache.cassandra.tcm.MultiStepOperation; +import org.apache.cassandra.tcm.Transformation; +import org.apache.cassandra.tcm.serialization.AsymmetricMetadataSerializer; +import org.apache.cassandra.tcm.serialization.MetadataSerializer; +import org.apache.cassandra.tcm.serialization.Version; +import org.apache.cassandra.tcm.transformations.FinishDropAccordTable; +import org.apache.cassandra.utils.JVMStabilityInspector; + +import static java.lang.String.format; +import static org.apache.cassandra.tcm.Transformation.Kind.FINISH_DROP_ACCORD_TABLE; +import static org.apache.cassandra.tcm.sequences.SequenceState.continuable; +import static org.apache.cassandra.tcm.sequences.SequenceState.error; +import static org.apache.cassandra.tcm.sequences.SequenceState.halted; +import static org.apache.cassandra.utils.Clock.Global.nanoTime; + +/** + * A slightly atypical implementation as it consists of only a single step. To perform the drop of an + * Accord table, we first commit a PrepareDropAccordTable transformation. Upon enactement, that + * marks the table as pending drop, which blocks any new transactions from being started. It also + * instantiates an instance of this operation and adds it to the set of in progress operations. + * + * The intention is to introduce a barrier which blocks until the Accord service acknowledges that + * it was learned of the epoch in which the table was marked for deletion and that all prior transactions + * are completed. Once this is complete, we can proceed to actually drop the table. The transformation + * which performs that schema modification also removes this MSO from ClusterMetadata's in-flight set. + * This obviates the need to 'advance' this MSO in the way that other implementations with more steps do. + * + */ +public class DropAccordTable extends MultiStepOperation<Epoch> +{ + private static final Logger logger = LoggerFactory.getLogger(DropAccordTable.class); + + public static final Serializer serializer = new Serializer(); + + public final TableReference table; + + /** + * Used by factory method for external callers and by the serializer. + * We don't need to include the serialized FinishDropAccordTable step in the serialization + * of the MSO itself because they have no parameters other than the table reference and so + * we can just construct a new one when we execute it + */ + private DropAccordTable(TableReference table, Epoch latestModification) + { + super(0, latestModification); + this.table = table; + } + + public static DropAccordTable newSequence(TableReference table, Epoch preparedAt) + { + return new DropAccordTable(table, preparedAt); + } + + @Override + public boolean equals(Object o) + { + if (this == o) return true; + if (o == null || getClass() != o.getClass()) return false; + DropAccordTable that = (DropAccordTable) o; + return latestModification.equals(that.latestModification) + && table.equals(that.table); + } + + @Override + public int hashCode() + { + return Objects.hash(latestModification, table); + } + + @Override + public Kind kind() + { + return Kind.DROP_ACCORD_TABLE; + } + + @Override + protected SequenceKey sequenceKey() + { + return table; + } + + @Override + public MetadataSerializer<? extends SequenceKey> keySerializer() + { + return TableReference.serializer; + } + + @Override + public Transformation.Kind nextStep() + { + return FINISH_DROP_ACCORD_TABLE; + } + + @Override + public SequenceState executeNext() + { + try + { + SequenceState failure = awaitSafeFromAccord(); + if (failure != null) return failure; + } + catch (Throwable t) + { + JVMStabilityInspector.inspectThrowable(t); + logger.warn("Exception while waiting for Accord service to notify all table txns are complete", t); + // this is actually continuable as we can simply retry + return continuable(); + } + try + { + // Now we're satisfied that all Accord txns have finished for the table, + // go ahead and actually drop it + ClusterMetadataService.instance().commit(new FinishDropAccordTable(table)); + return continuable(); + } + catch (Throwable t) + { + JVMStabilityInspector.inspectThrowable(t); + logger.warn("Exception committing finish_drop_accord_table. " + + "Accord service has acknowledged the operation but table remains present in schema", t); + return halted(); + } + } + + private SequenceState awaitSafeFromAccord() throws ExecutionException, InterruptedException + { + // make sure that Accord sees the current epoch, which must necessarily follow the + // one which marked the table as pending drop + ClusterMetadata metadata = ClusterMetadata.current(); + // just for the sake of paranoia, assert that the table is actually marked as being dropped + if (!verifyTableMarked(metadata.schema.getKeyspaces())) + return error(new IllegalStateException(String.format("Table %s is in an invalid state to be dropped", table.toCQLString()))); + + long startNanos = nanoTime(); + AccordService.instance().epochReady(metadata.epoch).get(); + long epochEndNanos = nanoTime(); + + //TODO (correctness, operability): this is more than likely to timeout, so best to "await" an existing txn_id rather than creating a new one... + AccordService.instance().awaitForTableDrop(table.id); + long awaitEndNanos = nanoTime(); + logger.info("Wait for Accord to see the drop table was success. " + + "Took {} to wait for Accord to learn about the change, then {} to process everything", + Duration.ofNanos(epochEndNanos - startNanos), Duration.ofNanos(awaitEndNanos - epochEndNanos)); + return null; + } + + private boolean verifyTableMarked(Keyspaces keyspaces) + { + TableMetadata tm = keyspaces.getTableOrViewNullable(table.id); + if (tm == null) + { + logger.warn("Unable to drop accord table {}, table not found", table); + return false; + } + + if (!tm.params.pendingDrop) + { + logger.warn("Unexpected state, table {} was not marked pending drop", table); + return false; + } + + return true; + } + + @Override + public Transformation.Result applyTo(ClusterMetadata metadata) + { + // note: that this will apply the finish drop transformation to the supplied metadata. It's + // not used to actually execute the MSO, but to determine what the metadata state will/would + // be if it were executed. + return new FinishDropAccordTable(table).execute(metadata); + } + + @Override + public DropAccordTable advance(Epoch epoch) + { + // note: this isn't really used by this MSO impl as it consists of a single step so there's nothing + // to advance. An action of the single step is to remove the MSO from the set of in progress sequences + return new DropAccordTable(this.table, epoch); + } + + @Override + public ProgressBarrier barrier() + { + return ProgressBarrier.immediate(); + } + + public static class TableReference implements SequenceKey, Comparable<TableReference> + { + public static final Serializer serializer = new Serializer(); + + public final String keyspace, name; + public final TableId id; + + public TableReference(String keyspace, String name, TableId id) + { + this.keyspace = normalize(keyspace); Review Comment: there was an issue I never figured out where the string matched but java said that they were not equal... after forcing the strings to be the same charset it started working, but then I switched to trying to find where it happened and it stopped happening... your comment is to drop the strings anyways... -- This is an automated message from the Apache Git Service. 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