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https://issues.apache.org/jira/browse/CASSANDRA-18934?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17811265#comment-17811265
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Claude Warren commented on CASSANDRA-18934:
-------------------------------------------
I don't think we can modify 4.x code for this purpose. I encountered the same
issue in the 4->3 downgrade. My solution was to rewrite the system tables that
need modification. System tables will need modification when columns have been
added or removed, or when column data types change. Non-system tables are
not affected because we can specify column addition/deletion/modification in
the schema table(s) to address the issues. But as Guo discovered the system
tables are hard coded in each version.
In the solution I arrived at I noted the column changes and then rewrote the
necessary tables during the downgrade process. This means that we have to
track, by hand, all the system table changes between version. To simplify
this, my original solution wrote the earliest form of the V3 table and let the
"we can read earlier versions" processes handle changing it to the proper
state. I cleaner solution might be to have the jars from the earlier version
available so that the prior classes can be loaded and interrogated to see if
there are changes and stop if there are any changes that the system can not
deal with.
> Downgrade to 4.1 fails due to schema changes
> --------------------------------------------
>
> Key: CASSANDRA-18934
> URL: https://issues.apache.org/jira/browse/CASSANDRA-18934
> Project: Cassandra
> Issue Type: Bug
> Components: Local/Startup and Shutdown
> Reporter: David Capwell
> Assignee: Maxwell Guo
> Priority: Normal
> Fix For: 5.x
>
>
> We are required to support 5.0 downgrading to 4.1 as a migration step, but we
> don’t have tests to show this is working… I wrote a quick test to make sure a
> change we needed in Accord wouldn’t block the downgrade and see that we fail
> right now.
> {code}
> ERROR 20:56:39 Exiting due to error while processing commit log during
> initialization.
> org.apache.cassandra.db.commitlog.CommitLogReadHandler$CommitLogReadException:
> Unexpected error deserializing mutation; saved to
> /var/folders/h1/s_3p1x3s3hl0hltbpck67m0h0000gn/T/mutation4184214444767150092dat.
> This may be caused by replaying a mutation against a table with the same
> name but incompatible schema. Exception follows: java.lang.RuntimeException:
> Unknown column compaction_properties during deserialization
> at
> org.apache.cassandra.db.commitlog.CommitLogReader.readMutation(CommitLogReader.java:464)
> at
> org.apache.cassandra.db.commitlog.CommitLogReader.readSection(CommitLogReader.java:397)
> at
> org.apache.cassandra.db.commitlog.CommitLogReader.readCommitLogSegment(CommitLogReader.java:244)
> at
> org.apache.cassandra.db.commitlog.CommitLogReader.readCommitLogSegment(CommitLogReader.java:147)
> at
> org.apache.cassandra.db.commitlog.CommitLogReplayer.replayFiles(CommitLogReplayer.java:191)
> at
> org.apache.cassandra.db.commitlog.CommitLog.recoverFiles(CommitLog.java:223)
> at
> org.apache.cassandra.db.commitlog.CommitLog.recoverSegmentsOnDisk(CommitLog.java:204)
> {code}
> This was caused by a schema change in CASSANDRA-18061
> {code}
> /*
> * 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.distributed.upgrade;
> import java.io.IOException;
> import java.io.File;
> import java.util.concurrent.atomic.AtomicBoolean;
> import org.junit.Test;
> import org.apache.cassandra.distributed.api.IUpgradeableInstance;
> public class DowngradeTest extends UpgradeTestBase
> {
> @Test
> public void test() throws Throwable
> {
> AtomicBoolean first = new AtomicBoolean(true);
> new TestCase()
> .nodes(1)
> .withConfig(c -> {
> if (first.compareAndSet(true, false))
> c.set("storage_compatibility_mode", "CASSANDRA_4");
> })
> .downgradeTo(v41)
> .setup(cluster -> {})
> // Uncomment if you want to test what happens after reading the commit log,
> which fails right now
> // .runBeforeNodeRestart((cluster, nodeId) -> {
> // IUpgradeableInstance inst = cluster.get(nodeId);
> // File f = new File((String)
> inst.config().get("commitlog_directory"));
> // deleteRecursive(f);
> // })
> .runAfterClusterUpgrade(cluster -> {})
> .run();
> }
> private void deleteRecursive(File f)
> {
> if (f.isDirectory())
> {
> File[] children = f.listFiles();
> if (children != null)
> {
> for (File c : children)
> deleteRecursive(c);
> }
> }
> f.delete();
> }
> }
> {code}
> {code}
> diff --git
> a/test/distributed/org/apache/cassandra/distributed/upgrade/UpgradeTestBase.java
>
> b/test/distributed/org/apache/cassandra/distributed/upgrade/UpgradeTestBase.java
> index 5ee8780204..b4111e3b44 100644
> ---
> a/test/distributed/org/apache/cassandra/distributed/upgrade/UpgradeTestBase.java
> +++
> b/test/distributed/org/apache/cassandra/distributed/upgrade/UpgradeTestBase.java
> @@ -226,6 +226,12 @@ public class UpgradeTestBase extends DistributedTestBase
> return this;
> }
> + public TestCase downgradeTo(Semver to)
> + {
> + upgrade.add(new TestVersions(versions.getLatest(CURRENT),
> Collections.singletonList(versions.getLatest(to))));
> + return this;
> + }
> +
> /**
> * performs all supported upgrade paths that exist in between from
> and to that include the current version.
> * This call is equivalent to calling {@code upgradesTo(from,
> CURRENT).upgradesFrom(CURRENT, to)}.
> {code}
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