Yes you need to create an index, what's your label called? Imagine it being called :NGram
create index on :NGram(gram);
match (n:NGram) where n.gram='0gram' AND n.word=~'a.' return n.word LIMIT 5
match (n:NGram) where n.gram='0gram' AND n.word=~'a.*' return n.word LIMIT 25
What you're doing is not a graph search but just a lookup via full scan + property comparison with a regexp. Not a very efficient operation. What you need is FullTextSearch (which is not supported with the new schema indexes but still with the legacy indexes).
Could you run this query (after you created the index) and say how many nodes it returns?
match (n:NGram) where n.gram='0gram' return count(*)
which is the equivalent to
match (n:NGram {gram:'0gram'}) return count(*)
I wrote a blog post about it a few days ago, please read it and see if it applies to your case.
How big is your Neo4j database on disk?
What is the configured heap size? (in neo4j-wrapper.conf
?)
As you can see you use more RAM than you machine has (not even counting OS or filesystem caches).
So you would have to reduce the mmio sizes, e.g. to 500M for nodes 2G for rels and 1G for properties.
Look at your store-file sizes and set mmio accordingly.