presto-main/src/main/java/io/prestosql/operator/PagesIndex.java/PagesIndex/clear
class PagesIndex:    public void clear()
    {
        for (ObjectArrayList<Block> channel : channels) {
            channel.clear();
            channel.trim();
        }
        valueAddresses.clear();
        valueAddresses.trim();
        positionCount = 0;
        nextBlockToCompact = 0;
        pagesMemorySize = 0;

        estimatedSize = calculateEstimatedSize();
    }