xmlWriterhave a very small memory footprint, only enough for the state information of the XML parser, and in the case of
xmlReader, the current element. The memory consumed stays relatively constant, regardless of the size of the XML document being dealt with.
xmlTreeinterface holds the entire tree in memory, and requires around 4 times the size of the XML document. For example, the XML-1.0 recommendation is about 150KB and, when parsed, uses around 650KB of memory.