Miles are my meditation

This is the second post in my series of Running free… A developers story of development.. In this part I will focus on what actually helped me defocus my head from spiralling around work related issues and problems.

Cognitive therapy – Miles are my meditation



In 2017, I was writing my second book, running the EuregJUG was a great success and on the outside, I was as successful as it get’s in my company, but I was feeling worse every day.

I tried a couple of things that I thought would be expected of a successful mid thirty guy (aka a dude with a full blown midlife crisis) and define myself better:

  • Went to fancy barbershops and got myself expensive haircuts
  • And an expensive watch
  • Drank more than ever
  • Tried to be what I thought is manly

Result: I looked stupid, spent to much money, got fat, sit in front of a computer even more. I needed a big shift of focus in my life, something like a cognitive therapy

I was always an avid cyclist and still managed to ride a bike nearly everyday. That was however also work related as I did commute by bike. Not much of a focus shift.

JCrete 2017



Sometimes all it needs is a good conversation and people being role models. I had a couple of those at JCrete 2017, especially with Felix and Heinz. I’m mentioning this here because of two reasons:

  • The conversations people lead are important and have often an effect.
  • If possible, go visit an unconference. JCrete is one of the most famous, but a couple of
    more have appeared in the last years, such as
    JAlba, JWild or JSpirit.

These unconferences offers a market place like proposal and selection of topics. Many of those pretty hard core technology wise but also with topics such as presented here.

Running – Is your bike broken



I always said that I start running on the day when all my bikes are broken.

I actually tried a couple of times to run more than a kilometer and I usually hit something like 3k and ended always at the point where everything hurt and while I’m usually quite stubborn, I couldn’t convince myself do go further.

Standard solution until then was trying to motivate me with buying more gear, but that was never longterm sustainable.

One doesn’t need much



The nice thing about running is: You can get pretty far with a decent pair of running shoes. It’s a good idea to go into a shop and get some guidance for selecting a pair. I needed one that gave me a bit of balance but not that much cushioning.

I have a couple of running shirts but depending on the lengths of your run, I don’t think they matter that much. I tend to sweat a lot, so I’m more for the lightweight sports gear that transports humidity away from the body. A fitness tracker is nice, but not required. I would even say a heart rate monitor is not necessary. Usually you will notice when you are over pacing, but alas, I’m not a doctor of medicine.

Anyway, this time, I stuck with my old pair of running shoes and set a couple of other goal:

SMART goals



Goals are important.

I really think that we all have a ton of intrinsic motivation in us. To access it we need goals and an environment that allows us to pursue those goals. Goals in the context of this talk here aren’t of course not only sport goals, but also professional ones. Those can be: Learning a new language (of course, both programming and spoken languages), solving the task of your job in an optimal way, making a relevant step in your career.

There are a lot of silly acronyms in project management and methodology but here’s one I really like: SMART goals. Those are goals that are:

  • Specific
  • Measurable
  • Achievable
  • Realistic
  • Timely

Let’s see: I wanted to be able to run 10k by the end of 2017 and get my weight down to 80kg again. That makes already two specific and measurable goals. Are they achievable? Of course. A healthy person at my age should be able to run 10k in a reasonable amount of time and 80kg is pretty much my optimal body mass index. Both goals are realistic (in contrast to let’s say being able to compete against world class athletes). And finally, it was in the summer of 2017, 6 months would be perfectly long and short enough to achieve those goals.

Did I reach them?

There’s a nice run at the end of each year in my place. This is where I wanted to see if I reached my goal.

That was 2017:



10k in about 50 Minutes. Not bad at all. I spare you the view of my scale, but I reached the weight goal, too.

Fast forward to 2019:



Where to find motivation?



I already gave that answer: Miles are my meditation. Doing long distance things has a calming and relaxing effect. Runners or cyclist high is a thing.

It’s like turning off the repetitive thoughts in your head that circle around issues, anxiety and problems.

It forces you to focus on your breathing, your body, yourself. On the next step hill or mile in front of you. Not some abstract thing in the future.

Competition?



I like doing races because they make me stretch. It’s not like that I’m trying to reach a certain place, but running with a lot of folks and a timer ticking actually increases your pace by a whole magnitude.

Also: It’s great running in places that are reserved otherwise for cars etc.

Fun fact: I never considered participating in a cycling road race. I find group rides with more than 5 or 6 people mentally straining enough already. In a peloton you’re usually super close to each other and you really have to be aware. Kinda defeats the purpose of switching ones head of for a while.

What about Medals? 🏅



Remember what I said at the beginning about outside appreciation: Medals, physical and virtual, are also that, so enjoy them, but they don’t matter anyway (at least when you’re not a professional racer, I guess).

In June 2018 I joined Strava…



and things escalated a bit. I never thought that a platform like Strava would change my life that much.

If it’s not on Strava, it didn’t happen

I smiled about that joke at first, but then gamification kicked in. See 2018, 2019 and now 2020:



In 2019, I went totally bonkers… Here again a goal: Doing a Strava “Gran Fondo” aka a 100k cycling tour each month and taking pictures. That was a fun thing to do… I even created a small book from it and donated the revenue.

Nice memories



I have been thinking about these now for some time.

I have been discussing Strava and gamification with my wife and also the kids. The kids love this physical medals and yes, even when I said earlier today, don’t rely too much on outside appreciation, kids being proud of their parents is a hell of a good appreciation.

And actually, having some real tokens fits the experience of doing a halve or a full marathon a lot more.

Being outside



The biggest motivation for me however is being outside. Doesn’t matter if on bikes or running. While I took all three pictures here near my home during pretty good weather, I ran and cycle the last two years with

  • rain
  • more rain
  • storm
  • snow
  • and everything in between

I found it much easier to go out running in bad conditions, the effort required to clean messed up gear is just smaller. Cycling usually means more inertia as you need to plastique wrap yourself and most of the time, wash the ride.

I used to listen to music the first couple of weeks while running but eventually stopped it. I don’t listen to podcasts. I try to don’t think about anything.

I cannot stress this enough: The brain also needs room to wonder and ruminate.

Zwift and generally indoor sports never clicked with me. They allow a lot of people to make the most of their time and I get this. Would I use something indoor sports, I would missing the bit of letting my brain go. Of course I would watch talks or TV shows.

How did the running influence me?



Feeling stronger and healthier

As plain as it is: I feel stronger and healthier.

More relaxed

Also, as simple as that: Working out, feeling yourself, your body and the surroundings and a hot shower afterwards does wonders, much more than the a lonesome leisure beer does.

For me, it worked wonders avoiding depersonalization.

More resilient

It made me more resilient: I needed to overcome an initial pain point.

The longer distances taught me that pace control is important. I can rush all the things I want in the beginning, if I cannot reach my goal, it’s in vain.

Let me tell you this story: I ran my first marathon in April 2019, started with an achievable goal time and try to run a constant pace to reach that. The second one, in October the same year I was like “Go all in”. That worked well enough for the first half of the thing and ended with me more or less crawling behind the finish line. In the end, I was only a minute faster than on the first one but at the same time, wore myself down.

Anyway, it’s the same with work: Make sure you’re in a place where you can find your pace. A good place will you give the time for that.

Positive feedback

The realization that I’m actually good at something I always disliked is eye opening.

If it works with sports, it probably works with other things, too. Things that might seem out of your comfort zone, too.

Like: Being more open in work, accepting help, accepting challenges that involves more than superficial reflections and so on.

Focus shift

Let’s focus on that one.

I had enough time to think while running and realized a couple of things:

  • I was more than overworked
  • I felt depersonalized and while being angry at a lot of things, actual success and good projects at work left me cold.
  • Lot’s of stuff was very robotic and tiresome at the same time
  • I took the anger with me home
  • While being stuck in it, I wasn’t able to articulate that.

So let’s raise the question: How did I let it come to this, even in surroundings where it would not be technically necessary. Why do we overwork?

Continue with part 3: Why do we overwork and burnout?

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23-Mar-20


Running free… A developers story of development.

This is gonna be the first of four parts accompanying my talk with the same name: Running free… A developers story of development. which I held in March 2020 at the inaugural launch of dev.next. I’m grateful that Venkat Subramaniam gave me the opportunity to do this.

Sadly, dev.next got cancelled respectively postponed due to the 2019–20 coronavirus pandemic.

I had created a readable version of the talk in hope anyone finds this motivating or can draw something for themselves out of it. I’m happy to have it now and I’m gonna share it in five parts over the coming weeks. If anyone finds it useful, I love to hear your feedback.

Overview

Running free… A developers story of development.



This is “Running free”, a talk about a developers story of development. In this post I will tell you bits and pieces of my story that I hope you might find useful.

This talks needs a couple of warnings. The first – and shorter warning – it’s a personal thing, the standard about me page doesn’t apply. The whole talk is probably an about page.

I am gonna share a lot of personal stories and more important, personal recipes and strategies to cope and tackle various things. It should be obvious, that these approaches may work or may not work for you. They work in most cases for me, but your milage will vary.

Am I the right person for this?



I’d say, it depends… On a good day, of course I am. I’m confident in what I am doing, I am aware that I’m good at what I am doing. On a bad day, probably not.

There are actually tons of days where I

  • Feel bad about me
  • Feel bad about the stuff I do
  • Overwork
  • Stress out (myself, my family and colleagues (Hello, Gerrit… ))

But… let’s focus on the good days and keep it with Dajana here:



While I actually have training and I am certified to train other people for a job in computer science, i am not a personal coach and I have never been trained in coaching other people. I can only share my experiences the same way a lot of people shared their experience with me.

The talk will contain a couple of quotes from people I like and whose input helped me to rethink a couple of things. People and the network you’ll build over the course of a career are much more important than technology. Always remember that: Value relationships, in both directions.

So, let’s get started: who is this developer?

About me (Standard Edition)



Let’s start with the usual “About me” slide. My name is Michael Simons. What do we have here:

I work for Neo4j, the graph database company. We have a lot of cool things out there. First of all, the graph database with the same name and then the thing that I’m working on with my friend Gerrit Meier: The Neo4j-OGM and Spring Data integration.

Of course I have to brag around that I’m one of the Java Champions. It’s one of these things that made me really proud, actually. How did it come to this?

The slide explains it as well: I’m the current lead for a Java user group named EuregJUG, which I have been running now in the 5th year with great success. In that role I’m also actively involved with the JavaLand conference. I’m also the author of a couple of books: The first german Spring Boot 2 book and “Arc42 by example”,

Before I was at Neo4j, I worked most of my professional life at ENERKO INFORMATIK in Aachen, Germany. In between I briefly worked as a senior consultant for the well known German consultancy INNOQ.

In good moments I am able to honestly say that I’m proud about all of these things. In some others, my imposter syndrome kicks in and doesn’t let me realize that this is actually something.

At this point you’d usually find the company slide or slides, depending on how much marketing and legal material one is obliged to show but I like to quote Sébastien from RedHat here:

We are not just developers.



Sébastien runs the Riviera Dev in France and they have a track named this way about exactly that topic.
We spoke briefly about this talk here and the track name immediately clicked with me for a couple of reasons.

Hopefully it is clear that thinking about yourself as a Java or .NET, as Go or Rust developer or whatever
language you prefer these days, narrows the number of options and choices you might have.
So from a professional point of view it is of course a good choice to think as “I’m a developer”.

But thinking of oneself as just a developer and probably focussing on gaining appreciation from that single source makes you vulnerable and insecure.

First of all, we are humans, with different needs and hopefully, different interests and resulting from that, different inputs.

About me (Additional Edition)



So, I am a father of two, a husband to a beautiful wife, I cycle, run, read and do a lot of more things. I am probably a few more other things.

The things I do change over time, sometimes but less often, the things I am do too. It’s important to distinguish between something you need to be and something you do. Those are not the same (and please don’t get me started about “I have a wife” vs “I am a husband” or the same with “I have two kids” vs “I am a parent”)!

Sometimes it is appropriate to include an additional slide like this one, sometimes it isn’t. I think this time it was.

Keep a slide like this in mind next time you feel bad about code, a project or work in general.

I am We are not…



Actually, I think we could avoid a whole category of problems in our job when we could remember a couple of easy things here:

  • We are not the code we wrote nor the project we maintain.
  • We are not the architecture of a system we are responsible for.

If we don’t keep these things in mind we’re in danger of drawing all our self worth from external opportunities. This makes reasoning and speaking about technical problems so much harder, even when the other people in the room are good colleagues and your project has a good discussion culture.

Why? Because getting self worth and appreciation from only a single thing is a single point of failure and as such, a pain in the ass. Even if it does not fail, it bothers and bugs us.

As alway, there are smarter people in the room. When I tweeted about this thoughts – quite exactly a year ago – Roman Kennke, Java VM Hacker and Principal Software Engineer at RedHat, responded like this:

Don’t rely on any outside appreciation



I appreciate it very much that Roman replied with can. I mean, this is endboss-level-hard. Anyone of us likes a casual “thank you”, a “well done”. Even more so some verbalization that something we did was helpful.

By all probability not only the younger people in the audience but anyone who is in one form or the other on social media looks for hearts, stars, thumb ups, followers and what not.

Stuff like this becomes addictive and you will have a hard time getting off from it. I’m not saying it’s completely bad, not at all, but mind the dosage.

Find things that you enjoy, preferable a broad range of things, make yourself less fragile and more resilient.

For me, those couple of statements already required some kind of focus shift. Getting my head and my thoughts away from recurring patterns and thoughts. A cognitive therapy, if you like, so let’s start with that.

Continue with part 2: Miles are my meditation.

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17-Mar-20


Polyglot programming on the GraalVM

(*) As of now R, Ruby, Python and JavaScript 😉

GraalVM consists of a Java Compiler, a VM and a JDK based on HotSpot/OpenJDK, implemented in Java. These days it’s all about additional execution modes compared to the standard JVM, mainly ahead-of-time compilation and the creation of native images. Native images are an important piece to create Java based applications that are easier to scale in very elastic ways and large deployments.

However, the GraalVM has a couple of more distinctive features:

  • Truffle Language Implementation framework and the GraalVM SDK, to implement additional programming language runtimes
  • LLVM Runtime and JavaScript Runtime

The content of this post is based on the Truffle framework and with it, the polyglot aspect of GraalVM.

There have been a couple of great talks about Graal and especially Polyglot. Have a look at Polyglot Applications with GraalVM from @mesirii and JS, Rust, Python and the Holy Graal by @larsr_h.

The GraalVM is polyglot in many different ways: You can embedded a supported guest language in a host language through a so called polyglot context but you can also call access all supported languages from a supported, dynamic language by running the GraalVM version of the interpreter with the --polyglot.

Inside the GraalVM manual you’ll find the polyglot reference as well as the embedding reference. The embedding reference is mostly about running supported languages from Java programs. This won’t be our concern in this post. This is about the polyglot reference. The examples in the manual are designed for first selecting a start language and then a target language. The examples follow the pattern that a host languages executes some simple code in the guest language.

Me friend Michael however nerd snipped me with a different idea: How to access Neo4j from R? Or use the multi database features from Neo4j 4.0 from a language for which we (I work at Neo4j at the drivers team) haven’t yet come up with a driver?

GraalVM polyglot interoperability for the win. You find information about GraalVM’s polyglot interoperability per language inside the manual, for example here for Ruby.

In short: The interpreters for the supported languages all comes with an API to interact with all other supported languages.

That allows us the Neo4j Java Driver in it’s current 4.0.0 mainline to from R, Python, Ruby and for completeness from JavaScript (the 4.0 JavaScript driver for Neo4j is already there) as well.

Michael and I have setup a repository named “neo4j-graalvm-polyglot-examples” that demonstrates this approach.

Setting up Neo4j

These example are about access to Neo4j from various languages. I find the easiest way to have an instance up in running in no time is Docker.

docker run --publish=7474:7474 --publish=7687:7687 -e 'NEO4J_AUTH=neo4j/secret' neo4j:4.0.1

gives you a running instance. After that, you can open http://localhost:7474/browser/?cmd=play&arg=movies and install our Movie graph to have a dataset to work with.

Other options include our Desktop edition which you find among other downloads here: https://neo4j.com/download/

Setting up GraalVM

Michael Hunger uses SDKMan! for downloading and installing GraalVM, I went to the GraalVM Downloads page at GitHub and got the JDK 11 edition of GraalVM 20.0.0.

After downloading and installing, you should have a valid GRAALVM_HOME and a JAVA_HOME pointing to the former:

echo $GRAALVM_HOME 
/Library/Java/JavaVirtualMachines/graalvm-ce-java11-20.0.0/Contents/Home
✗ echo $JAVA_HOME
/Library/Java/JavaVirtualMachines/graalvm-ce-java11-20.0.0/Contents/Home
✗ java -version
openjdk version "11.0.6" 2020-01-14
OpenJDK Runtime Environment GraalVM CE 20.0.0 (build 11.0.6+9-jvmci-20.0-b02)
OpenJDK 64-Bit Server VM GraalVM CE 20.0.0 (build 11.0.6+9-jvmci-20.0-b02, mixed mode, sharing)

GraalVM comes with gu, the GraalVM Component Updater. gu is used to install additional packages. We use it to install R, Ruby and Python packages as well as the native image tool for GraalVM:

$GRAALVM_HOME/bin/gu install R
$GRAALVM_HOME/bin/gu install Ruby     
$GRAALVM_HOME/bin/gu install Python
$GRAALVM_HOME/bin/gu install native-image

The list of installed components should now look likes this:

$GRAALVM_HOME/bin/gu list                
 
ComponentId              Version             Component name      Origin 
--------------------------------------------------------------------------------
graalvm                  20.0.0              GraalVM Core        
R                        20.0.0              FastR               github.com
llvm-toolchain           20.0.0              LLVM.org toolchain  github.com
native-image             20.0.0              Native Image        github.com
python                   20.0.0              Graal.Python        github.com
ruby                     20.0.0              TruffleRuby         github.com

JS respectively Node come by default with GraalVM.

Running the examples

The examples live in neo4j-graalvm-polyglot-examples. Clone this repository via standard Git means. The Neo4j driver lives under the Maven coordinates org.neo4j.driver:neo4j-java-driver. The driver has a single dependency to the reactive stream API. To make the download easier, the repository comes with a Gradle build that works both under Windows and Linux. Get and export the required dependencies via

./gradlew downloadDependencies
export CLASSPATH=lib/neo4j-java-driver-4.0.0.jar:lib/reactive-streams-1.0.2.jar

All examples can now be run like this:

# R
$GRAALVM_HOME/bin/Rscript --jvm --vm.cp=$CLASSPATH neo4j-graalvm-fastr-example.R
 
# Javascript
$GRAALVM_HOME/bin/node --jvm --vm.cp=$CLASSPATH neo4j-graalvm-javascript-example.js
 
# Python
$GRAALVM_HOME/bin/graalpython --jvm --vm.cp=$CLASSPATH neo4j-graalvm-python-example.py
 
# Ruby
$GRAALVM_HOME/bin/truffleruby --jvm --vm.cp=$CLASSPATH neo4j-graalvm-ruby-example.rb

They all execute the following query

MATCH (:Person {name:$name})-[:ACTED_IN]->(m)<-[:ACTED_IN]-(coActor) 
RETURN DISTINCT coActor

The query has one parameter called name and gives you all the actors that acted in the same movie like the request actor.

I take neo4j-graalvm-fastr-example.R as example, but the idea is the same for all the examples above.

First, you have to import the required classes via GraalVM’s Java API:

graphDatabase <- java.type('org.neo4j.driver.GraphDatabase')
authTokens <- java.type('org.neo4j.driver.AuthTokens')
config <- java.type('org.neo4j.driver.Config')

With our static factory method, a database connection is opened:

driver <- graphDatabase$driver('bolt://localhost:7687', authTokens$basic('neo4j', 'secret'), config$defaultConfig())

It looks similar in all the other languages. The Neo4j drivers are session oriented. That means, the driver instance is a long living object you keep around and the session is used for your tasks. The driver takes care of connection pooling.

Executing the above query looks like this in R:

query <- '
    MATCH (:Person {name:$name})-[:ACTED_IN]->(m)<-[:ACTED_IN]-(coActor) 
    RETURN DISTINCT coActor
'
 
session <- driver$session()
# The R list (which behaves like an associative array) is automatically converted to a Java Map 
coActorsRecords <- session$run(query, list(name="Tom Hanks"))$list()

This gives you a list of records that can be processed further.

Recap

The GraalVM is a fascinating piece of software. We are not combining trivial libraries in those examples, but loading a driver that manages a connection pool based on an embedded Netty.

While it is of course preferable to have everything “natively” to your language, a polyglot environment like this gives you the opportunity to use foreign functions without that much effort. It wouldn’t be that hard to wrap our Java driver with idiomatic code for someone that has actual R knowledge to make it feel like first class R citizen.

Another use case is to have access to all features of Neo4j 4.0, for example the multi database feature. This is not yet available in the Python driver or the community driven Ruby driver. Here’s an example on how to use them: Python and Ruby.

The official, native Neo4j drivers that are already fully Neo4j 4.0 are here:

The Python driver will be released the coming weeks with full 4.0 support.

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06-Mar-20


Spring Data Neo4j, Neo4j-OGM and OSIV

TL;DR: Don’t use Open Session in View with a Neo4j-Cluster

If you use Spring Data Neo4j and Neo4j-OGM in your Spring Boot application connectect against a Neo4j cluster (via bolt+routing://, neo4j:// or multiple bolt-uris), configure spring.data.neo4j.open-in-view explicitly to false like this: spring.data.neo4j.open-in-view=false

What is Open Session in View?

Vlad Mihalcea has written extensive amounts about why the Open Session in View Pattern is an Anti pattern these days.

Vlad is well known for his work in JPA and especially hibernate world. What the hell has this to do with Spring Data Neo4j and Neo4j’s Object Graph Mapping (Neo4j-OGM)? It turns out, a lot. We have to bring a couple of things together.

Neo4j routing

This is maybe unexpected, but the first thing we have to understand is Neo4j’s routing mechanism. Neo4j databases are able to run as clusters. The instances of those clusters use the Raft consensus algorithm. Part of that algorithm are leaders, followers and read replicas.

My colleague David allen has a nice post out there on how to query a Neo4j cluster: Querying Neo4j Clusters.

The important stanza for this post is:

The leader is responsible for coordinating the cluster and accepting all writes. Followers help scale the read workload ability of the cluster and provide for high-availability of data. Should one of the cluster machines fail, and you still have a majority, you can still process reads and writes. If your cluster loses the majority it can only serve (stale) reads and has no leader anymore.

Optionally, you can have any number caches in the form of read replicas. They are read-only copies of your database for scaling out read-query load. They are not officially part of the cluster, but rather are “tag along” copies that get replicated transactions from the main cluster.

When you connect to a cluster one of the Neo4j drivers does the job of routing for you everytime you open a connection via the bolt+routing:// respectivly neo4j://. It is said that “the driver is connected to a cluster”. The driver has a routing table, knowing leader, follower and read replicas.

The driver does not parse Cypher on the client side. The only information it has available to pick a host from the routing table is whether you want a read session or a read-write session respectivly transaction. Therefor it is very important to make that choice consciously! Otherwise all request will go to the leader, as that instance will be able to answer all of them.

Neo4j-OGM

Neo4j-OGM is able to support Neo4j cluster and routing via it’s Bolt transport. There are a couple of convience methods on the Neo4j-OGM session that let’s you specify whether it’s a read or a read-write statement you want to run. Neo4j-OGM actually does look into your Cypher and issues a warning if you ask for a read-only transaction but have something like MERGE, CREATE or UPDATE in your Cypher.

So up here it’s all good.

Entering Spring’s @Transactional

Spring’s @Transactional is a great piece of code. It instructs the framework to execute your code in a transactional around aspect: A transaction is opened before your code and closed afterwards, commiting if your code ran without error, rolling back otherwise. A transaction manager takes care that this also works with a explicit TransactionTemplate.

The annotation has an attribute named readOnly. In contrast to a superficial look at it, it doesn’t prevent writes to happen against a database. And how could it? @Transactional is a general purpose mechanism, working with JPA, Neo4j and other databases. It would need mechanisms to find out about your query for all of those. readOnly is merely an indicator to be passed on to the underlying store so that this store configure characteristics as needed. Vlad has written down what it does for Hibernate.

For Neo4j-OGM it just configures the default mode of the Driver’s session: read only or read-write. As we learned above, this is super important to prevent the leader from being hammered by all the queries.

Spring Data Neo4j and Neo4j-OGM supports this in all of the following scenarios, given the following repository and service:

import java.util.Collection;
import java.util.Collections;
import java.util.List;
 
import org.neo4j.ogm.session.Session;
import org.springframework.data.neo4j.annotation.Query;
import org.springframework.data.neo4j.repository.Neo4jRepository;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
 
public interface MovieRepository extends Neo4jRepository<Movie, Long> {
 
	@Transactional(readOnly = true)
	@Query("MATCH (m:Movie) RETURN m.tagline as value")
	List<SomeResult> findCustomResultWithTxOnRepository();
 
	// Not read only
	@Query("MATCH (m:Movie) RETURN m.tagline as value")
	List<SomeResult> findCustomResult();
}
 
 
@Service
public class SomeService {
 
	private final MovieRepository movieRepository;
 
	private final Session session;
 
	public SomeService(MovieRepository movieRepository, Session session) {
		this.movieRepository = movieRepository;
		this.session = session;
	}
 
	@Transactional(readOnly = true)
	public Collection<SomeResult> findCustomResultWithTransactionOnService() {
 
		return movieRepository.findCustomResult();
	}
 
	@Transactional(readOnly = true)
	public Collection<Movie> findMoviesViaLoadAllOnSession() {
 
		return session.loadAll(Movie.class);
	}
 
	@Transactional(readOnly = true)
	public Collection<Movie>findMoviesViaCustomQueryOnSession() {
 
		return (Collection) session.query(Movie.class, "MATCH (m:Movie) RETURN m", Collections.emptyMap());
	}
}

All of those understand that none of the queries needs to go to a leader.

Entering OSIV

For Neo4j-OGM, there’s also an OpenSessionInViewInterceptor that get’s configured via Spring Boot by default in a web application. It makes sure there’s an ongoing Neo4j-OGM session along with it’s caches and mapping in place for the whole request.

Why is this bad in a cluster scenario? Because tied to the Neo4j-OGM session there’s the driver session. To allow the user to do anything they want in the request, those sessions need to be read-write sessions. Once marked as read-write, you cannot make turn read only ever again.

That means if you call any of the above scribbeld methods from a REST endpoint, there will already be an ongoing session and the readOnly indicator will be ignored!

So if you connect a Spring Data Neo4j + Neo4j-OGM application against a Neo4j cluster: Go to your Spring Boot configuration (either properties or YAML or Environment) and explicity configure:

spring.data.neo4j.open-in-view=false

I have raised an issue with the Spring Boot team to discuss changing the default: Open session in view is problematic with Neo4j..

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03-Feb-20


Short end of the year status update.

Last year – 2018 – I ended up with 21 post on my blog, this one here, the last of this decade at this blog, will be the 11th of 2019. What happened?

I have been working more than ever, and happier than ever. Together with Gerrit Meier, we managed to bring down the open issues on Neo4j-OGM under ten (without just closing them) and at the same time designing two new projects: A Spring Boot Starter for Neo4j without any object mapping at all and SDN/RX, a new object mapping framework with a focus on reactive database access.

I started the year with a lot of JUG talks (see my Speakerdeck), in the Netherlands, in Switzerland and a couple in Germany. In between, we did a couple of talks at the EuregJUG as well.

So, busy times for blogging, at least on this platform.

I posted several Neo4j related posts on Medium. I personally like this one the best: How to choose an unique identifier for your database entities. I think it applies to other systems, too. You’ll find more interesting content at our Medium Neo4j magazine.

Late November, Ralf nerd-snipped me to participate in Advent of Code and wow, I got hit for good. I managed to come up with not only two stars each day, but a blog post as well for 13 days in December. Find my solutions at Ralf’s fan site Christina just bluntly told me after the tenth day: “Stop it, your mood is getting increasingly worse.” and that was a good thing to do.

I submitted some Call for Papers next year, mostly about reactive programming with Neo4j and Spring Data Neo4j RX and with a bit of luck, I’ll be at some conferences.

The one thing I’m looking very much forward however is dev.next in March 2020:

2019 has one of the most rewarding years I had in my professional and private life. While a casual reader of my blog might probably think “well, that guy is just doing fine”, that’s not always true. I often struggle, make mistakes and bad things happen. I’m gonna talk about some conscious decisions – like the one above, stop doing things (AoC) – and some things that might look like decisions but might have been just a couple of lucky coincides.

Anyway, until then, have a good holiday season at the end of the year and all the best for 2020.

Featured photo by Trent Erwin on Unsplash.

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23-Dec-19