presto-spi/src/main/java/io/prestosql/spi/PageBuilder.java/PageBuilder/getRetainedSizeInBytes
class PageBuilder:    public long getRetainedSizeInBytes()
    {
        // We use a foreach loop instead of streams
        // as it has much better performance.
        long retainedSizeInBytes = 0;
        for (BlockBuilder blockBuilder : blockBuilders) {
            retainedSizeInBytes += blockBuilder.getRetainedSizeInBytes();
        }
        return retainedSizeInBytes;
    }