presto-memory/src/main/java/io/prestosql/plugin/memory/MemoryMetadata.java/MemoryMetadata/getColumnHandles
class MemoryMetadata:    @Override
    public synchronized Map<String, ColumnHandle> getColumnHandles(ConnectorSession session, ConnectorTableHandle tableHandle)
    {
        MemoryTableHandle handle = (MemoryTableHandle) tableHandle;
        return tables.get(handle.getId())
                .getColumns().stream()
                .collect(toMap(ColumnInfo::getName, ColumnInfo::getHandle));
    }