6.1. Cypher query options

This section describes the query options available in Cypher.

Query execution can be fine-tuned through the use of query options. In order to use one or more of these options, the query must be prepended with CYPHER, followed by the query option(s), as exemplified thus: CYPHER query-option [further-query-options] query.

6.1.1. Cypher version

Occasionally, there is a requirement to use a previous version of the Cypher compiler when running a query. Here we detail the available versions:

Query option Description Default

3.5

This will force the query to use Neo4j Cypher 3.5.

 

4.0

This will force the query to use Neo4j Cypher 4.0. As this is the default version, it is not necessary to use this option explicitly.

X

In Neo4j 4.1, the support for Cypher 3.5 is provided only at the parser level. The consequence is that some underlying features available in Neo4j 3.5 are no longer available and will result in runtime errors.

Please refer to the discussion in Cypher Compatibility for more information on which features are affected.

6.1.2. Cypher runtime

Using the execution plan, the query is executed — and records returned — by the Cypher runtime. Depending on whether Neo4j Enterprise Edition or Neo4j Community Edition is used, there are three different runtimes available:

Interpreted
In this runtime, the operators in the execution plan are chained together in a tree, where each non-leaf operator feeds from one or two child operators. The tree thus comprises nested iterators, and the records are streamed in a pipelined manner from the top iterator, which pulls from the next iterator and so on.
Slotted
This is very similar to the interpreted runtime, except that there are additional optimizations regarding the way in which the records are streamed through the iterators. This results in improvements to both the performance and memory usage of the query. In effect, this can be thought of as the 'faster interpreted' runtime.
Pipelined

The pipelined runtime was introduced in Neo4j 4.0 as a replacement for the older compiled runtime used in the Neo4j 3.x versions. It combines some of the advantages of the compiled runtime in a new architecture that allows for support of a wider range of queries.

Algorithms are employed to intelligently group the operators in the execution plan in order to generate new combinations and orders of execution which are optimised for performance and memory usage. While this should lead to superior performance in most cases (over both the interpreted and slotted runtimes), it is still under development and does not support all possible operators or queries (the slotted runtime covers all operators and queries).

Option Description Default

runtime=interpreted

This will force the query planner to use the interpreted runtime.

This is not used in Enterprise Edition unless explicitly asked for. It is the only option for all queries in Community Edition—​it is not necessary to specify this option in Community Edition.

runtime=slotted

This will cause the query planner to use the slotted runtime.

This is the default option for all queries which are not supported by runtime=pipelined in Enterprise Edition.

runtime=pipelined

This will cause the query planner to use the pipelined runtime if it supports the query. If the pipelined runtime does not support the query, the planner will fall back to the slotted runtime.

This is the default option for some queries in Enterprise Edition.

In Enterprise Edition, the Cypher query planner selects the runtime, falling back to alternative runtimes as follows:

  • Try the pipelined runtime first.
  • If the pipelined runtime does not support the query, then fall back to use the slotted runtime.
  • Finally, if the slotted runtime does not support the query, fall back to the interpreted runtime. The interpreted runtime supports all queries, and is the only option in Neo4j Community Edition.

6.1.3. Cypher replanning

Cypher replanning occurs in the following circumstances:

There may be situations where Cypher query planning can occur at a non-ideal time. For example, when a query must be as fast as possible and a valid plan is already in place.

Replanning is not performed for all queries at once; it is performed in the same thread as running the query, and can block the query. However, replanning one query does not replan any other queries.

There are three different replan options available:

Option Description Default

replan=default

This is the planning and replanning option as described above.

X

replan=force

This will force a replan, even if the plan is valid according to the planning rules. Once the new plan is complete, it replaces the existing one in the query cache.

 

replan=skip

If a valid plan already exists, it will be used even if the planning rules would normally dictate that it should be replanned.

 

The replan option is prepended to queries. For example:

CYPHER replan=force MATCH ...

In a mixed workload, you can force replanning by using the Cypher EXPLAIN commands. This can be useful to schedule replanning of queries which are expensive to plan, at known times of low load. Using EXPLAIN will make sure the query is only planned, but not executed. For example:

CYPHER replan=force EXPLAIN MATCH ...

During times of known high load, replan=skip can be useful to not introduce unwanted latency spikes.