1.Introduce CustomScan into openGauss
CustomScan is a powerful PostgreSQL feature that allows developers to extend the
query executor by implementing custom scan providers. This enables integration of
specialized data sources or optimization techniques that aren't natively supported
by PostgreSQL.
a. CustomScan node: A plan node that represents the custom scan operation
b. CustomScan methods: Callbacks that implement the scan behavior
c. CustomScan provider: The extension that registers the custom scan implementation
CustomScan is an advanced feature primarily used by extension developers to deeply
integrate specialized data processing capabilities with PostgreSQL's query executor.
add transaction callbacks interface before commit and prepare stage.
extenal extension can use those interface to participate opengauss's
transaction model.
2.adapt bgworker for plugin.
3.Add spq build adaption
4.Fit for extensible plan/extensible node.
5.Allow auth logic to continue search after found an rule with remote trust but the
connection is not from coordinator.
