Large graph causes sql query issues

[sheridana]

When attempting to process a large graph I run into sql query issues:

psycopg2.errors.InternalError_: invalid memory alloc request size 1073741824

which is triggered by this line

should this be updated to process in batches? probably here

[sheridana]

@pattonw as discussed, adding:

if roi is None:
     node_condition = "true"

to read_edges() is a quick fix. The problem then remains for the case when we need to process a large roi if the query then doesn't fit in memory. Adding a join is likely necessary.