[jira] [Commented] (HADOOP-15708) Reading values from Configuration before adding deprecations make it impossible to read value with deprecated key

["Robert Kanter (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-15708?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16636272#comment-16636272 ] 

Robert Kanter commented on HADOOP-15708:
----------------------------------------

There's definitely something wrong here.  I was playing with the {{Configuration}} class like this:
{code:java}
// OLD_KEY is set to "foo" in the XML
conf.get(OLD_KEY);  // returns "foo"
Configuration.addDeprecations(OLD_KEY, NEW_KEY);
conf.get(OLD_KEY);  // returns null
{code}
That doesn't seem right.  Adding a deprecation looks like it breaks getting the value of the deprecated key.  On top of that, if you ommit the 2nd line, it works correctly:
{code:java}
// OLD_KEY is set to "foo" in the XML
Configuration.addDeprecations(OLD_KEY, NEW_KEY);
conf.get(OLD_KEY);  // returns "foo"
{code}
This means that getting the {{OLD_KEY}} and then deprecating it changes the value, which isn't the right behavior.  

As for the right way to fix this, and make sure we're not breaking anything depending on this odd behavior, I'm not sure.  It would be good to get some more opinions.

> Reading values from Configuration before adding deprecations make it impossible to read value with deprecated key
> -----------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-15708
>                 URL: https://issues.apache.org/jira/browse/HADOOP-15708
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: conf
>    Affects Versions: 3.2.0
>            Reporter: Szilard Nemeth
>            Assignee: Zoltan Siegl
>            Priority: Minor
>         Attachments: HADOOP-15708-testcase.patch, HADOOP-15708.001.patch, HADOOP-15708.002.patch, HADOOP-15708.003.patch
>
>
> Hadoop Common contains a widely used Configuration class.
>  This class can handle deprecations of properties, e.g. if property 'A' gets deprecated with an alternative property key 'B', users can access property values with keys 'A' and 'B'.
>  Unfortunately, this does not work in one case.
>  When a config file is specified (for instance, XML) and a property is read with the config.get() method, the config is loaded from the file at this time. 
>  If the deprecation mapping is not yet specified by the time any config value is retrieved and the XML config refers to a deprecated key, then the deprecation mapping specified, the config value cannot be retrieved neither with the deprecated nor with the new key.
>  The attached patch contains a testcase that reproduces this wrong behavior.
> Here are the steps outlined what the testcase does:
>  1. Creates an XML config file with a deprecated property
>  2. Adds the config to the Configuration object
>  3. Retrieves the config with its deprecated key (it does not really matter which property the user gets, could be any)
>  4. Specifies the deprecation rules including the one defined in the config
>  5. Prints and asserts the property retrieved from the config with both the deprecated and the new property keys.
> For reference, here is the log of one execution that actually shows what the issue is:
> {noformat}
> Loaded items: 1
> Looked up property value with name hadoop.zk.address: null
> Looked up property value with name yarn.resourcemanager.zk-address: dummyZkAddress
> Contents of config file: [<?xml version="1.0"?>, <configuration>, <property><name>yarn.resourcemanager.zk-address</name><value>dummyZkAddress</value></property>, </configuration>]
> Looked up property value with name hadoop.zk.address: null
> 2018-08-31 10:10:06,484 INFO  Configuration.deprecation (Configuration.java:logDeprecation(1397)) - yarn.resourcemanager.zk-address is deprecated. Instead, use hadoop.zk.address
> Looked up property value with name hadoop.zk.address: null
> Looked up property value with name hadoop.zk.address: null
> java.lang.AssertionError: 
> Expected :dummyZkAddress
> Actual   :null
> {noformat}
> *As it's visible from the output and the code, the issue is really that if the config is retrieved either with the deprecated or the new value, Configuration both wants to serve the value with the new key.*
>  *If the mapping is not specified before any retrieval happened, the value is only stored under the deprecated key but not the new key.*



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