[teiid-issues] [JBoss JIRA] Resolved: (TEIID-600) Better handling of connector depdendencies

[Steven Hawkins (JIRA)]

     [ https://jira.jboss.org/jira/browse/TEIID-600?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Steven Hawkins resolved TEIID-600.
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    Resolution: Done


This fix now unifies connector/extension loading for both embedded and server.  A full description of embedded classloading is:

App ClassLoader - Possibly from a container loads the client jar
  Lib ClassLoader - loads all applicable entries from lib/patches in the embedded install
    Post delegating lib override ClassLoader - from TEIID-590 prevents version conflicts between our lib and the lib's parent
      Common extension ClassLoader - A shared classloader initialized from the common extension property (TEIID-418).  Connector and other dependencies are added dynamically as need.  Extension module changes trigger a reload of this shared class loader. 
        Post delegating Connector ClassLoader - optionally created if the connector property UsePostDelegation is set to true, then the connector classpath and connector type classpath entries are loaded in their own classloader (which can also be cached).

The only connectors that set UsePostDelegation to true are xml and salesforce.  All of the others are allowed to add their dependencies at runtime into the shared common extension classloader.  The advantages of this approach:
- Allows connectors to optionally use a delegating classloader in an efficient manner.  This fixes the issue observed with the oracle driver - of course the user can still put their dependencies in the lib if desired.
- Does not require any changes to the Designer.
- Is the same for embedded/server

Connector developers must still be cautious - if a custom connector introduces a conflicting dependency then it must have the UsePostDelegation flag set to true.  In the rare case of a post delegating connector that also has a dependency that needs to be delegating, then the entry must be removed from the appropriate connector classpath and manually added to the common extension classpath property. 



> Better handling of connector depdendencies
> ------------------------------------------
>
>                 Key: TEIID-600
>                 URL: https://jira.jboss.org/jira/browse/TEIID-600
>             Project: Teiid
>          Issue Type: Quality Risk
>          Components: Connector API
>    Affects Versions: 6.0.0
>            Reporter: Steven Hawkins
>            Assignee: Steven Hawkins
>            Priority: Critical
>             Fix For: 6.1.0
>
>
> Connector dependencies by in large really fall into two categories - our built-in jars or jars that are intended to be at a system level (such as a driver).  By only allowing these jars to exist under a post delegation class loader there are many downsides - it has a negative impact on memory, it can cause issues with classloader leaks, makes built in connector patching more difficult, and simply won't work in the case of native oracle drivers.  Here are the steps we would like to take to address this:
> Promote all top-level built-in connector jars to the lib - this would be things like connector-jdbc, connector-ldap, etc.
> Add the notion of the common extension classpath to the dqp.
> Change the common extension classpath to be a delegating classloader.
> Change the meaning of the connector classpath to "required common dependencies", then at the start of any connector service ensure/add all entries from the connector classpath into the common extension classpath.  The common extension classpath will be cached and managed similar to the connector classloader cache.  Changes to extension modules will cause it to be reloaded.  Since this approach does not actually threat connector classpath setting as a classpath ordering of the entries doe not matter and thus patch jars would not be useful in this setting.  Rather users would simply replace the extension module they are attempting to patch.
> The connector type classpath would remain and still specifies required post delegation libraries. 
> How Designer is managing dependencies does not need to initially change at all.  Basically all jars added as connector dependencies will be treated as common.  The only scenario that won't work initially is a custom connector requiring post-delegation libraries.  We can address this at a later time.   

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