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https://issues.apache.org/jira/browse/DRILL-5660?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16082460#comment-16082460
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Paul Rogers edited comment on DRILL-5660 at 7/11/17 4:28 PM:
-------------------------------------------------------------
Sounds good.
In other projects, we did not find the need to use new classes each time there
is a version. Instead, we write the code so that the serializer writes the
current version, but the deserializer uses if statements to handle old versions.
A highly simplified example, changing foo from an int to a string.
{code}
void serialize() {
writeProperty("version", 4);
writeProperty("foo", "10x");
...
}
void deserialize() {
version = readIntProperty("version");
if (version < 4) {
foo = Integer.toString( readIntProperty("foo") );
} else {
foo = readStringProperty("foo);
}
}
{code}
Obviously, if the internal data structures change, it may be easier to create a
new derived class. But, there is really no need: the old class is no longer
needed: we have to convert the old structures to the new format on read.
The above technique was used across 10 years and dozens of version changes.
Maintaining dozens of classes would have been quite difficult...
For this particular issue, we are just writing relative paths, and either
converting relative paths to absolute (current version), or using the existing
absolute paths (older versions), so no new classes should be needed.
Note, please also coordinate with DRILL-4139 as that issues will also introduce
a new metadata version number.
was (Author: paul-rogers):
Sounds good.
In other projects, we did not find the need to use new classes each time there
is a version. Instead, we write the code so that the serializer writes the
current version, but the deserializer uses if statements to handle old versions.
A highly simplified example, changing foo from an int to a string.
{code}
void serialize() {
writeProperty("version", 4);
writeProperty("foo", "10x");
...
}
void deserialize() {
version = readIntProperty("version");
if (version < 4) {
foo = Integer.toString( readIntProperty("foo") );
} else {
foo = readStringProperty("foo);
}
}
{code}
Obviously, if the internal data structures change, it may be easier to create a
new derived class. But, there is really no need: the old class is no longer
needed: we have to convert the old structures to the new format on read.
The above technique was used across 10 years and dozens of version changes.
Maintaining dozens of classes would have been quite difficult...
> 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
> Fix For: 1.11.0
>
>
> 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 file.
> 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 for.
> Of course, it is highly desirable that newer servers read old files, but that
> is not the issue here.
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