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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5660) Drill 1.10 queries fail due to Parquet Metadata "corruption" from DRILL-3867
Date Wed, 26 Jul 2017 10:32:00 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5660?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16101515#comment-16101515

ASF GitHub Bot commented on DRILL-5660:

Github user arina-ielchiieva commented on a diff in the pull request:

    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/MetadataVersions.java
    @@ -0,0 +1,115 @@
    + * 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
    + * <p/>
    + * http://www.apache.org/licenses/LICENSE-2.0
    + * <p/>
    + * 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.drill.exec.store.parquet;
    +import com.google.common.collect.Lists;
    +import org.apache.drill.common.Version;
    +import org.apache.drill.common.exceptions.DrillRuntimeException;
    +import java.util.List;
    +import java.util.regex.Matcher;
    +import java.util.regex.Pattern;
    + * Supported metadata versions.
    + * <p>
    + * Note: keep them synchronized with {@link Metadata.ParquetTableMetadataBase} versions
    + */
    +public class MetadataVersions {
    +  static final org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(Metadata.class);
    +  /**
    +   * Version 1: Introduces parquet file metadata caching.<br>
    +   * See DRILL-2743
    +   */
    +  public static final String V1 = "v1";
    +  /**
    +   * Version 2: Metadata cache file size is reduced.<br>
    +   * See DRILL-4053
    +   */
    +  public static final String V2 = "v2";
    +  /**
    +   * Version 3: Difference between v3 and v2 : min/max, type_length, precision, scale,
repetitionLevel, definitionLevel.<br>
    +   * Filter pushdown for Parquet is implemented. <br>
    +   * See DRILL-1950
    +   */
    +  public static final String V3 = "v3";
    +  /**
    +   * Version 3.1: Absolute paths of files and directories are replaced with relative
    +   * See DRILL-3867
    +   */
    +  public static final String V3_1 = "v3.1";
    +  /**
    +   * All historical versions of the Drill metadata cache files
    +   */
    +  public static final List<String> SUPPORTED_VERSIONS = Lists.newArrayList(V1,
V2, V3, V3_1);
    --- End diff --
    How developer will know which pattern is used to add versions? If developer adds incorrect
version, we will be able to find out if it's correct only during version comparison thus in
Drill runtime.  We need to provide a better mechanism to ensure that the next version is correctly
formed. Taking into account that in parser you already need some parquet metadata version
entity, I guess we can think about creating such entity:
    1. It would have two constructors, one for major and minor versions, the second one for
string representation. It would be able to parse string into itself so we can get rid off
parser class.
    2. It would be comparable.
    3. It would have `toString` method that will return string representation we actually
expect. Example: `new MetadataVersion(3, 1).toString()` -> `v3.1`
    4. `hashCode` and `equals` should be overridden.

> Drill 1.10 queries fail due to Parquet Metadata "corruption" from DRILL-3867
> ----------------------------------------------------------------------------
>                 Key: DRILL-5660
>                 URL: https://issues.apache.org/jira/browse/DRILL-5660
>             Project: Apache Drill
>          Issue Type: Bug
>    Affects Versions: 1.11.0
>            Reporter: Paul Rogers
>            Assignee: Vitalii Diravka
>              Labels: doc-impacting
> Drill recently accepted a PR for the following bug:
> DRILL-3867: Store relative paths in metadata file
> This PR turned out to have a flaw which affects version compatibility.
> The DRILL-3867 PR changed the format of Parquet metadata files to store relative paths.
All Drill servers after that PR create files with relative paths. But, the version number
of the file is unchanged, so that older Drillbits don't know that they can't understand the
> Instead, if an older Drill tries to read the file, queries fail left and right. Drill
will resolve the paths, but does so relative to the user's HDFS home directory, which is wrong.
> What should have happened is that we should have bumped the parquet metadata file version
number so that older Drillbits can’t read the file. This ticket requests that we do that.
> Now, one could argue that the lack of version number change is fine. Once a user upgrades
Drill, they won't use an old Drillbit. But, things are not that simple:
> * A developer tests a branch based on a pre-DRILL-3867 build on a cluster in which metadata
files have been created by a post-DRILL-3867 build. (This has already occurred multiple times
in our shop.)
> * A user tries to upgrade to Drill 1.11, finds an issue, and needs to roll back to Drill
1.10. Doing so will cause queries to fail due to seemingly-corrupt metadata files.
> * A user tries to do a rolling upgrade: running 1.11 on some servers, 1.10 on others.
Once a 1.11 server is installed, the metadata is updated ("corrupted" from the perspective
of 1.10) and queries fail.
> Standard practice in this scenario is to:
> * Bump the file version number when the file format changes, and
> * Software refuses to read files with a version newer than the software was designed
> Of course, it is highly desirable that newer servers read old files, but that is not
the issue here.

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