Hi Fazith,
for the call "getDataAsString()"
the data will be got from result set. if you do not have any data bound component like crosstab or chart, this call causes that the result set is fetched from source system (BW, HANA) to the Java stack. This means complete result set is pulled. Then the selection will be done (and this should not have too much performance effect). also, if you have 2 such calls on same data source, the second should not fetch the resultset again (unless you change filters or variables in between).
for the call "getMemberList()"
this needs to ask the source system for the members independent of the result set - therefore this is not causing any fetch of result set. But when you request many members (1000+) the transfer is taking also place (there is some cache in Java stack, so the second call should not always call again the fetch).
good practice is to use URL parameter in local mode (also on BIP) &PROFILING=X, then all the calls are visible in the statistics.
Karol