Limit should not be pushed down if there are unconverted restrictions

[kaidaguerre]

We only push down the limit to the plugin if all the where clauses are for key columns (with a supported operator). In this case, tags is not a key column so we should not be pushing down the limit.

Postgres passes the where clauses as restrictions which our FDW attempts to evaluate and convert into a Qual struct which is passed to the plugin. Sometimes we are unable to do this conversion. That is the case here:

SELECT region, instance_id, tags->>'Name' as name,  metadata_options['HttpEndpoint'] as HttpEndpoint, metadata_options['HttpTokens'] as HttpTokens FROM aws.aws_ec2_instance WHERE tags->>'Name' LIKE '%web%' LIMIT 1;

we cannot (currently) convert the Jsonb addressing syntax from a Postgres restriction into a Qual.

The limit pushdown logic does not take this into account, it just checks for successfully converted quals, so we are pushing down
the limit even though there is a non-key column where clause.

The fix is to update the pushdown logic to not pushdown if there are any unconverted restrictions. This will be in the upcoming release.