neo4j/cypher: Getting the hang of query parameters
For as long as I’ve been using neo4j's cypher query language Michael has been telling me to use parameters in my queries but the performance of the queries was always acceptable so I didn’t feel the need.
However, recently I was playing around with a data set and I created ~500 nodes using code similar to this:
require 'open-uri'
open("data/people.cyp", 'w') { |f|
(1..500).each do |value|
f.puts("CREATE (p:Person{name: \"#{value}\"})")
end
}That creates a file of cypher statements that look like this:
CREATE (:Person{name: "person1"})
CREATE (:Person{name: "person2"})
CREATE (:Person{name: "person3"})
CREATE (:Person{name: "person4"})
CREATE (:Person{name: "person5"})
...If we execute those statements in the neo4j-shell or web admin we get the following output:
==> +-------------------+
==> | No data returned. |
==> +-------------------+
==> Nodes created: 500
==> Properties set: 500
==> Labels added: 500
==> 27706 msAs far as I understand the reason it takes that long is that cypher creates and then caches a query plan for each create statement because it has no way of knowing that they are effectively the same.
Since I was deleting/reloading the data quite frequently I wanted to make my feedback loop a bit quicker so it was finally time to apply Michael’s advice.
The way that parameters work is that you add placeholders into your cypher queries and then provide values that should reify those placeholders when you execute your query.
In this case it seemed easiest to make use of neography to execute my query against a running neo4j server.
If we want to create a single person with a parameterised name then we’d write the following code:
require 'neography'
params = { :name => "Mark" }
Neography::Rest.new.execute_query("CREATE (:Person {name: {name} })", params)If we run a query to get back all people we can see they’ve been successfully created:
neo4j-sh (0)$ match p:Person return p;
==> +----------------------+
==> | p |
==> +----------------------+
==> | Node[1]{name:"Mark"} |
==> +----------------------+
==> 1 row
==> 175 msI wanted to pass in an array of names which I initially thought I could do but changing the value in the params hash to an array:
require 'neography'
params = { :name => [] }
(1..500).each do |value|
params[:name] << "person#{value}"
end
Neography::Rest.new.execute_query("CREATE (:Person {name: {name} })", params)I ran a query to get back my 500 people but only got one back:
neo4j-sh (0)$ MATCH p:Person RETURN p
> ;
==> +-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------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==> | p |
==> +-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------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==> | Node[1]{name:["person1","person2","person3","person4","person5","person6","person7","person8","person9","person10","person11","person12","person13","person14","person15","person16","person17","person18","person19","person20","person21","person22","person23","person24","person25","person26","person27","person28","person29","person30","person31","person32","person33","person34","person35","person36","person37","person38","person39","person40","person41","person42","person43","person44","person45","person46","person47","person48","person49","person50","person51","person52","person53","person54","person55","person56","person57","person58","person59","person60","person61","person62","person63","person64","person65","person66","person67","person68","person69","person70","person71","person72","person73","person74","person75","person76","person77","person78","person79","person80","person81","person82","person83","person84","person85","person86","person87","person88","person89","person90","person91","person92","person93","person94","person95","person96","person97","person98","person99","person100","person101","person102","person103","person104","person105","person106","person107","person108","person109","person110","person111","person112","person113","person114","person115","person116","person117","person118","person119","person120","person121","person122","person123","person124","person125","person126","person127","person128","person129","person130","person131","person132","person133","person134","person135","person136","person137","person138","person139","person140","person141","person142","person143","person144","person145","person146","person147","person148","person149","person150","person151","person152","person153","person154","person155","person156","person157","person158","person159","person160","person161","person162","person163","person164","person165","person166","person167","person168","person169","person170","person171","person172","person173","person174","person175","person176","person177","person178","person179","person180","person181","person182","person183","person184","person185","person186","person187","person188","person189","person190","person191","person192","person193","person194","person195","person196","person197","person198","person199","person200","person201","person202","person203","person204","person205","person206","person207","person208","person209","person210","person211","person212","person213","person214","person215","person216","person217","person218","person219","person220","person221","person222","person223","person224","person225","person226","person227","person228","person229","person230","person231","person232","person233","person234","person235","person236","person237","person238","person239","person240","person241","person242","person243","person244","person245","person246","person247","person248","person249","person250","person251","person252","person253","person254","person255","person256","person257","person258","person259","person260","person261","person262","person263","person264","person265","person266","person267","person268","person269","person270","person271","person272","person273","person274","person275","person276","person277","person278","person279","person280","person281","person282","person283","person284","person285","person286","person287","person288","person289","person290","person291","person292","person293","person294","person295","person296","person297","person298","person299","person300","person301","person302","person303","person304","person305","person306","person307","person308","person309","person310","person311","person312","person313","person314","person315","person316","person317","person318","person319","person320","person321","person322","person323","person324","person325","person326","person327","person328","person329","person330","person331","person332","person333","person334","person335","person336","person337","person338","person339","person340","person341","person342","person343","person344","person345","person346","person347","person348","person349","person350","person351","person352","person353","person354","person355","person356","person357","person358","person359","person360","person361","person362","person363","person364","person365","person366","person367","person368","person369","person370","person371","person372","person373","person374","person375","person376","person377","person378","person379","person380","person381","person382","person383","person384","person385","person386","person387","person388","person389","person390","person391","person392","person393","person394","person395","person396","person397","person398","person399","person400","person401","person402","person403","person404","person405","person406","person407","person408","person409","person410","person411","person412","person413","person414","person415","person416","person417","person418","person419","person420","person421","person422","person423","person424","perso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|
==> +-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------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==> 1 rowI’d actually made use of parameters in such a way that only one person got created and had their 'name' property set to an array of 500 names!
I tweaked the code to pass in an array of maps instead of strings like so:
require 'neography'
params = { :people \=> [] } (1..500).each do |value|
params[:people] << { :name \=> "person#\{value}"}
end
Neography::Rest.new.execute_query("CREATE (:Person \{people})", params)I ran my script to populate the database before querying it again:
neo4j-sh (0)$ MATCH p:Person RETURN p;
=\=> +-----------------------------+ =\=> | p | =\=> +-----------------------------+ =\=> | Node[1]{name:"person1"} | =\=> | Node[2]{name:"person2"} | =\=> | Node[3]{name:"person3"} | =\=> | Node[4]{name:"person4"} | =\=> | Node[5]{name:"person5"} | =\=> | Node[6]{name:"person6"} | =\=> | Node[7]{name:"person7"} | =\=> | Node[8]{name:"person8"} | =\=> | Node[9]{name:"person9"} | =\=> | Node[10]{name:"person10"} | =\=> | Node[11]{name:"person11"} | \... =\=> +-----------------------------+ =\=> 500 rows =\=> 1081 msThis time I got the expected result so the only thing to do was to quickly check how long it had taken to get the parameterised data into the database:
$ time bundle exec ruby people.rb
real 0m0.993s
user 0m0.733s
sys 0m0.097sAnd the winner is…Michael, by about 26 seconds per run.
In this version cypher creates a query plan the first time it encounters the CREATE statement but after that it can use the query plan for the subsequent calls which leads to a massive performance improvement.
Alistair pointed out that the query parameter approach is quite nice when used in applications because you don’t need to worry about string concatenation, you can just change values in maps instead.
Based on this experience I can now confirm Max De Marzi's tweet from last week:
Public Service Announcement for folks new to @https://twitter.com/neo4j[neo4j] and Cypher: Please use parameters in your queries http://docs.neo4j.org/chunked/milestone/cypher-parameters.html #MuchFaster
About the author
I'm currently working on short form content at ClickHouse. I publish short 5 minute videos showing how to solve data problems on YouTube @LearnDataWithMark. I previously worked on graph analytics at Neo4j, where I also co-authored the O'Reilly Graph Algorithms Book with Amy Hodler.