Query tuning

Neo4j aims to execute queries as fast as possible. However, when optimizing for maximum query execution performance, it may be helpful to rephrase queries using knowledge about the domain and the application.

This page contains information about how to tune queries using different strategies.

For information about changing the runtime of a query, see the page about Cypher^® runtime concepts.

General recommendations

The overall goal of manual query performance optimization is to ensure that only necessary data is retrieved from the graph.

Queries should aim to filter data as early as possible in order to reduce the amount of work that has to be done in the later stages of query execution. This also applies to what gets returned: returning whole nodes and relationships ought to be avoided in favour of selecting and returning only the data that is needed. You should also make sure to set an upper limit on variable length patterns, so they don’t cover larger portions of the dataset than needed.

Each Cypher query gets optimized and transformed into an execution plan by the Cypher query planner. To minimize the resources used for this, try to use parameters instead of literals when possible. This allows Cypher to re-use queries instead of having to parse and build new execution plans.

To read more about the execution plan operators mentioned in this section, see Operators.

Query options

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

For information about the various runtimes available in Cypher, see Cypher runtimes.

Cypher planner

The Cypher planner takes a Cypher query and computes an execution plan that solves it. For any given query there is likely a number of execution plan candidates that each solve the query in a different way. The planner uses a search algorithm to find the execution plan with the lowest estimated execution cost.

This table describes the available planner options:

Query option Description Default

planner=cost

Use cost based planning with default limits on plan search space and time.

planner=idp

Synonym for planner=cost.

planner=dp

Use cost based planning without limits on plan search space and time to perform an exhaustive search for the best execution plan.

Using this option can significantly increase the planning time of the query.

Cypher connect-components planner

One part of the Cypher planner is responsible for combining sub-plans for separate patterns into larger plans - a task referred to as connecting components.

This table describes the available query options for the connect-components planner:

Query option Description Default

connectComponentsPlanner=greedy

Use a greedy approach when combining sub-plans.

Using this option can significantly reduce the planning time of the query.

connectComponentsPlanner=idp

Use the cost based IDP search algorithm when combining sub-plans.

Using this option can significantly increase the planning time of the query but usually finds better plans.

The Cypher query option connectComponentsPlanner is deprecated and will be removed without a replacement. The product’s default behavior of using a cost-based IDP search algorithm when combining sub-plans will be kept.

Cypher update strategy

This option affects the eagerness of updating queries.

The possible values are:

Query option Description Default

Query option	Description	Default
`updateStrategy=default`	Update queries are executed eagerly when needed.
`updateStrategy=eager`	Update queries are always executed eagerly.

updateStrategy=default

Update queries are executed eagerly when needed.

updateStrategy=eager

Update queries are always executed eagerly.

Cypher expression engine

This option affects how the runtime evaluates expressions.

The possible values are:

Query option Description Default

Query option	Description	Default
`expressionEngine=default`	Compile expressions and use the compiled expression engine when needed.
`expressionEngine=interpreted`	Always use the interpreted expression engine.
`expressionEngine=compiled`	Always compile expressions and use the compiled expression engine.

expressionEngine=default

Compile expressions and use the compiled expression engine when needed.

expressionEngine=interpreted

Always use the interpreted expression engine.

expressionEngine=compiled

Always compile expressions and use the compiled expression engine.

Cypher operator engine

This query option affects whether the pipelined runtime attempts to generate compiled code for groups of operators.

The possible values are:

Query option Description Default

Query option	Description	Default
`operatorEngine=default`	Attempt to generate compiled operators when applicable.
`operatorEngine=interpreted`	Never attempt to generate compiled operators.
`operatorEngine=compiled`	Always attempt to generate compiled operators. Cannot be used together with `runtime=slotted`.

operatorEngine=default

Attempt to generate compiled operators when applicable.

operatorEngine=interpreted

Never attempt to generate compiled operators.

operatorEngine=compiled

Always attempt to generate compiled operators.

Cannot be used together with runtime=slotted.

Cypher interpreted pipes fallback

This query option affects how the pipelined runtime behaves for operators it does not directly support.

The available options are:

Query option Description Default

interpretedPipesFallback=default

Equivalent to interpretedPipesFallback=whitelisted_plans_only.

interpretedPipesFallback=disabled

If the plan contains any operators not supported by the pipelined runtime then another runtime is chosen to execute the entire plan.

Cannot be used together with runtime=slotted.

interpretedPipesFallback=whitelisted_plans_only

Parts of the execution plan can be executed on another runtime. Only certain operators are allowed to execute on another runtime.

Cannot be used together with runtime=slotted.

interpretedPipesFallback=all

Parts of the execution plan may be executed on another runtime. Any operator is allowed to execute on another runtime. Queries with this option set might produce incorrect results, or fail.

Cannot be used together with or runtime=slotted.

This setting is experimental, and using it in a production environment is discouraged.

Cypher replanning

Cypher replanning occurs in the following circumstances:

When the query is not in the cache. This can either be when the server is first started or restarted, if the cache has recently been cleared, or if server.db.query_cache_size was exceeded.
When the time has past the dbms.cypher.min_replan_interval value, and the database statistics have changed more than the dbms.cypher.statistics_divergence_threshold value.

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

Option	Description	Default
`replan=default`	This is the planning and replanning option as described above.
`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.

replan=default

This is the planning and replanning option as described above.

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.

Cypher infer schema parts

For some queries, the planner can infer predicates such as labels or types from the graph structure, thereby enhancing its ability to estimate the number of rows each operator will produce. (See Understanding execution plans - Reading execution plans for more information about the role of operators and estimated row counts in query execution plans.) The option inferSchemaParts controls the extent to which the planner should infer predicates.

Option Description

Option	Description
`inferSchemaParts=off`	No predicates are inferred.
`inferSchemaParts=most_selective_label`	Relationship types are used to infer labels on connected nodes. The label corresponding to the smallest number of nodes is used to estimate rows. Avoiding the inference of multiple labels improves accuracy for nodes with several dependent labels, such as every `:Actor` being a `:Person`.

inferSchemaParts=off

No predicates are inferred.

inferSchemaParts=most_selective_label

Relationship types are used to infer labels on connected nodes. The label corresponding to the smallest number of nodes is used to estimate rows. Avoiding the inference of multiple labels improves accuracy for nodes with several dependent labels, such as every :Actor being a :Person.

If this query option is not provided, then the value set in Operations Manual → Configuration settings → dbms.cypher.infer_schema_parts will be used.