presto-postgresql/src/main/java/io/prestosql/plugin/postgresql/PostgreSqlClient.java/PostgreSqlClient/hstoreWriteFunction
class PostgreSqlClient:    private BlockWriteFunction hstoreWriteFunction(ConnectorSession session)
    {
        return (statement, index, block) -> {
            checkArgument(block instanceof SingleMapBlock, "wrong block type: %s. expected SingleMapBlock", block.getClass().getSimpleName());
            Map<Object, Object> map = new HashMap<>();
            for (int i = 0; i < block.getPositionCount(); i += 2) {
                map.put(varcharMapType.getKeyType().getObjectValue(session, block, i), varcharMapType.getValueType().getObjectValue(session, block, i + 1));
            }
            statement.setObject(index, Collections.unmodifiableMap(map));
        };
    }