SyncSchema generates a simplified representation of the postgres schema It assumes that conn has the `replication` flag set so that it can fetch the current tx log sequence number, and will error if not.

Col is the name and index of a column in a table.

ForeignKey represents a foreign key relationship the ForeignKey named "name" indicates that the columns "cols" on Table "foreignTable" references the primary key columns "cols" of "primaryTable".

PrimaryKey is the name of a primary key field in a table.

Schema represents a set of Tables and the tx log sequence number (XLogPos) at which they were fetched.

Table is associated with a set of PrimaryKeys and a set of ForeignKeys.