Creating property-less nodes in Neo4j - neo4j

Question

I have a schema like (:A)-[:TYPE_1]-(:B)-[:TYPE_2]-(:A). I need to link [:TYPE_1] and [:TYPE_2] Relationships to certain other Nodes (Say, types C,D,E etc.). I had to create some Nodes without any properties, like (:A)-[:TYPE_1]-(:Action)--(:B)--(:Action)-[:TYPE_2]-(:A). The only purpose of the (:Action) Nodes is to enable me to link the action to some other Nodes (because I can't link a relationship to a Node). Thus, there are no properties associated with them. Since I changed my schema, I am finding that MERGE queries have slowed down incredibly. Obviously, I can't index the (:Action) Nodes, but all other Indexes are in place. What could be going wrong?
Edit:
My logic is that 1) There are multiple csv files 2) Each row in each file provides one (a1:A)-[:TYPE_1]-(type_1:Action)--(b:B)--(type_2:Action)-[:TYPE_2]-(a2:A) pattern. 3) Two different files may provide the same a1,a2 and b entities. 4) However, if the file pertains to a1, it will give qualifiers for type_1 and if the file pertains to a2, it will give qualifiers for type_2. 5) Hence, I do an OPTIONAL MATCH to see if the pattern exists. 6) If it doesn't, I create the pattern, qualifying either type_1, or type_2 based on a parameter in the row called qualifier, which can be type_1 or type_2. 7) If it does, then I just qualify the type_1 or type_2 as the case may be.
statement = """
MERGE (file:File {id:$file})
WITH file
UNWIND $rows as row
MERGE (a1:A {id:row.a1})
ON CREATE
SET a1.name=row.a1_name
MERGE (a2:A {id:row.a2})
ON CREATE
SET a2.name=row.a2_name
MERGE (b:B {id:row.b})
ON CREATE
SET b.name = row.b_name,
MERGE (c:C {id:row.c})
MERGE (d:D {id:row.d})
MERGE (e:E {id:row.e})
MERGE (b)-[:FROM_FILE]->(file)
WITH b,c,d,e,a1,a2,row
OPTIONAL MATCH (a1)-[:TYPE_1]->(type_1:Action)-[:INITIATED]->(b)<-[:INITIATED]-(type_2:Action)<-[:TYPE_2]-(a2)
WITH a1,b,a2,row,c,d,e,type_1,type_2
CALL apoc.do.when(type_1 is null,
"WITH a1,b,a2,row,c,d,e
CALL apoc.do.when(row.qualifier = 'type1',
'CREATE (type_1:Action)
CREATE (type_2:Action)
MERGE (a1)-[:TYPE_1 ]->(type_1)-[:INITIATED]->(b)<-[:INITIATED]-(type_2)<-[:TYPE_2 ]-(a2)
MERGE (type_1)-[:WITH_C]->(c)
MERGE (type_1)-[:WITH_D]->(d)
MERGE (type_1)-[:WITH_E]->(e)',
'CREATE (type_1:Action)
CREATE (type_2:Action)
MERGE (a1)-[:TYPE_1]->(type_1)-[:INITIATED]->(b)<-[:INITIATED]-(type_2)<-[:TYPE_2 ]-(a2)
MERGE (type_2)-[:WITH_C]->(c)
MERGE (type_2)-[:WITH_D]->(d)
MERGE (type_2)-[:WITH_E]->(e)',
{row:row,a1:a1,a2:a2,b:b,c:c,d:d,e:e})
YIELD value
RETURN value",
"
WITH row,c,d,e,type_1,type_2
CALL apoc.do.when(row.qualifier = 'type1',
'MERGE (type_1)-[:WITH_C]->(c)
MERGE (type_1)-[:WITH_D]->(d)
MERGE (type_1)-[:WITH_E]->(e)',
'MERGE (type_2)-[:WITH_C]->(c)
MERGE (type_2)-[:WITH_D]->(d)
MERGE (type_2)-[:WITH_E]->(e)',
{row:row,type_1:type_1,type_2:type_2,c:c,d:d,e:e})
YIELD value
RETURN value",
{row:row,a1:a1,a2:a2,b:b,c:c,d:d,e:e,type_1:type_1,type_2:type_2})
YIELD value
RETURN count(*) as count
"""
params = []
for row in df.itertuples():
params_dict = {'a1': row[1], 'a1_name': row[-3],'a2':row[2],'a2_name':row[-4],'b_name':row[3],'b':row[-2],'c':int(row[6]),'d':row[7],'e':row[5],'qualifier':row[-1]}
params.append(params_dict)
if row[0] % 5000 == 0:
graph.run(statement, parameters = {"rows" : params,'file':file})
params = []
graph.run(statement, parameters = {"rows" : params,'file':file})

Answer 1

It's hard to say exactly what the issue is but I do notice that you use MERGE a bit more than you actually need to. In your apoc.do.when call you call
MERGE (a1)-[:TYPE_1 ]->(type_1)-[:INITIATED]->(b)<-[:INITIATED]-(type_2)<-[:TYPE_2 ]-(a2)
even though you know that you just created type_1 and type_2 so none of the relationships exist. If you change that to a CREATE you should see a speedup. The same logic applies to the other MERGE calls in that statement.