Introduce PluginInstaller

[skrzypo987]

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# Section
* Fix some things. ({issue}`issuenumber`)

[martint]

What would a such a plugin do if Trino is not aware of it and doesn’t know how to use it?

Please describe the motivation for this change.

[kokosing]

What would a such a plugin do if Trino is not aware of it and doesn’t know how to use it?

@martint One can use io.trino.server.Server#getAdditionalModules to inject support for custom functionality.

Also please notice #16066 that also presents the value of PluginInstaller to Trino itself. Thanks to this PluginManager follows open-close principle whenever a new type of the plugin is added.

[martint]

But a plugin needs to be inserted somewhere in the flow of a query. How would plugins added via a PluginInstaller be injected into the flow if the engine has no idea what the plugin is for?

[kokosing]

But a plugin needs to be inserted somewhere in the flow of a query.

Yes, for example SystemSecurityMetadata can be customized as we are using optional binder. Then custom plugin may affect it is behavior.

However, my motivation was to allow plugin to affect behavior of other processes than query execution that were added to customized Trino. IMO allowing changes of query behavior should be only allowed only with dedicated SPI. Query execution is too complex to be reasonably customized.

[martint]

However, my motivation was to allow plugin to affect behavior of other processes than query execution that were added to customized Trino.

You don’t need a plugin for that. You can just bind additional Guice modules to extend the Trino server if you need additional functionality.

It’s still not clear to me what problem we’re trying to solve.

[kokosing]

You don’t need a plugin for that. You can just bind additional Guice modules to extend the Trino server if you need additional functionality.

Yes. But if you want to have this functionality in the plugin, behind the plugin classloader isolation and as part of the bigger plugin then additional plugins are not enough.