Explanation of error “Database constraints have changed (txId=xxxxx) after this transaction (txId=yyyyy) started, which is not yet supported”

The following error, via bin/neo4j-shell: Database constraints have changed (txId=84) after this transaction (txId=81) started, which is not yet supported. Please retry your transaction to ensure all constraints are executed. or as logged in log/debug.log (3.x) or graph.db/messages.log (2.3.x): 2016-10-18… Read more →

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Tuning Cypher queries by understanding cardinality

Cardinality issues are the most frequent culprit in slow or incorrect Cypher queries. Because of this, understanding cardinality, and using this understanding to manage cardinality issues, is a critical component in Cypher query tuning, and query correctness in general. A… Read more →

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Properly escaping input data for neo4j-import

Note neo4j-import is intended to populate a new, empty database. It cannot be used to import into an existing database. When importing data using neo4j-import, make sure to review the required CSV file structure and considerations before moving on. http://neo4j.com/docs/stable/import-tool.html… Read more →

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Redirect Neo4j logs to sysout (using rsyslog)

Sometimes – due to organizational requirements, security, indexing or plain convenience – we want to output all of our application logs to Linux’s sysout. While Neo4j doesn’t offer this feature, we can use RSYSLOG (www.rsyslog.com) to achieve that and we… Read more →

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Using the ACTUAL data type with neo4j-import

When importing data using neo4j-admin import, make sure to review the required CSV file structure and considerations before moving on. https://neo4j.com/docs/operations-manual/current/tools/import/ ACTUAL vs. String (default) or Integer: Each node in the CSV must have an :ID, which can be in… Read more →

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Export a (sub)graph to Cypher script and import it again

Oftentimes you want to export a full (or partial) database to a file and import it again without copying the actual database files. If you want to do the latter, use neo4j-admin dump/load. Here are two ways on how to… Read more →

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Explanation of error LOAD CSV error of “Couldn’t load the external resource …​”

When running a LOAD CSV Cypher statement, for example LOAD CSV WITH HEADERS FROM “http://10.12.1.2/Neo4j/cities.csv” AS row WITH row create (c:cities {name:row.city}); whether through bin/neo4j-shell or the browser at http://localhost:7474 this may result in an error as follows Couldn’t load… Read more →

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How do I configure init and max java heap when running bin/neo4j-backup

When running $NEO4J_HOME/bin/neo4j-backup if a Java out of heap/memory error occurs you may want define the init and max Java heap to be used by neo4j-backup. The default behavior is to allow the JVM to define the init and max… Read more →

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Performing match intersection

Match intersection is a common use case where you’re searching for nodes which have relationships to all of a set of input nodes. For the rest of the article we’ll use the built-in movies graph for demonstration. The example use… Read more →

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Updating a node but returning its state from before the update

Some use cases require updating node (or relationship) properties, but returning the node (or relationship) as it was prior to the update. You’ll need to get a ‘snapshot’ of the node before the update, and return that snapshot instead of… Read more →

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How to List and Install Neo4j Versions Using yum

Warning Prior to Neo4j 3.2, the rpm distribution of Neo4j was experimental at this time. Use with caution and we advise installing from the linux tarball in production environments. For Neo4j 3.2 please follow the instructions here Neo4j 3.0 does… Read more →

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How do I set max open files for Debian installs

When perfoming an install of Neo4j using the Debian install kit and as detailed at https://neo4j.com/docs/operations-manual/current/deployment/single-instance/debian/, upon completion you will need to configure the linux configuration option for max files. If not configured you may encounter errors with a stack… Read more →

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How do I monitor linux open file usage

Linux users are typically configured with a maximum number of files to be opened. This is describe at based upon your installation method. To monitor how many open files a user has one can run lsof -u <user> replacing <user>… Read more →

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Number of open files

Linux platforms impose an upper limit on the number of concurrent files a user may have open. This number is reported for the current user and session with the ulimit -n command: user@localhost:~$ ulimit -n 1024 Neo4j will also report… Read more →

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