Neo4j-查询性能下降

Question

Here is my query:

MATCH (p:Publisher)-[r:PUBLISHED]->(w:Woka)-[s:AUTHORED]-(a:Author) 
MATCH (l:Language)-[t:USED]->(w:Woka) 
WHERE (a.author_name =~ '.*Camus.*' and a.author_name =~ '.*Albert.*') 
RETURN p.publisher_name, w.woka_title, a.author_name, l.language_name;

The first time this is executing the result is returned in 3.8 seconds. For the second execution couple minutes later the result is returned in 15.1 seconds. The more I am executing the longer the response time. For the third execution the response time is increasing and several moments later I am getting the results between 30 and 90 seconds.

I am the only user of this (development) database. No data is added or deleted or changed there. No indexes are dropped or created also there. When closing two out of three connections to the database the response time goes back to 15 seconds.

Memory is set 4GB as init and max up to 8GB. Server has 16GB total memory.

What is happening here? Why the response time differs so much?

Answer 1

How big is your graph? Could be that it allocates a lot of heap for caching and then there is not enough space for running the queries without garbage collection.

I presume your relationships are all 1:n, if not add a WITH distinct p,w,a in between the two matches.

Your query is also suboptimal, and will probably create a lot of intermediate results, you can use PROFILE to look at the query plan.

Try this:

PROFILE
MATCH (a:Author)
WHERE (a.author_name =~ '.*Camus.*' and a.author_name =~ '.*Albert.*') 
MATCH (p:Publisher)-[:PUBLISHED]->(w:Woka)<-[:AUTHORED]-(a)
MATCH (l:Language)-[:USED]->(w:Woka) 
RETURN p.publisher_name, w.woka_title, a.author_name, l.language_name;

Answer 2

I borrowed from other solutions and I changed the params as following in the file conf/neo4j.properties (server restarted after that):

neostore.nodestore.db.mapped_memory=512M
neostore.relationshipstore.db.mapped_memory=512M
neostore.propertystore.db.mapped_memory=512M
neostore.propertystore.db.strings.mapped_memory=512M
neostore.propertystore.db.arrays.mapped_memory=512M

The results are now returning, in average, 300% faster narrowing the time from 90 seconds to 30 seconds and I am not getting disconnected anymore from the web interface to the database.