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Metadata

Bolt protocol specifies additional data that can be sent along with the requested results. Such data is called metadata and can be divided into two groups:

  • Query Statistics
  • Notifications

Both of these metadata can be accessed through summary map that is being sent along with the results of the query. Query statistics will be under stats key, and notifications under notifications key.

Query Statistics​

Query statistics will be sent whenever a user executes a query that will affect data in any way. In other words we will track the quantity of these changes throughout the query execution and report it back to the user.

The structure of statistics is a map of string keys and integer values. Data that is being tracked:

  • nodes-created
  • nodes-deleted
  • relationships-created
  • relationships-deleted
  • labels-added
  • labels-removed
  • properties-set

This data will refer only to the changes done by the query, thus changes made in triggers will not affect these values.

Differences compared to triggers

It is possible that after executing a query some of these counters are not zero, however the regarding triggers are not triggered. The reason for that is triggers are only triggered when there is a difference between the starting and ending state, while the counters are also counting the not permanent changes.

For example if the query creates and deletes nodes like CREATE (n) DELETE n;, then it leaves Memgraph in the same state as before. The value will be 1 for both nodes-created and nodes-deleted, but the triggers will not be triggered since there is no difference between in states before and after the query is executed.

Notifications​

Notifications will be sent whether we want to confirm the results of query or want to notify the user about possible wrong usage. Every notification is represented as a dictionary with these possible values:

KeyValue Type
severityString
codeString
titleString
descriptionString

In order to enable users to handle these notifications however they see fit, we will introduce possible values for severity and code notifications attributes. Title and description values will depend on query and the query values and should be used only as messages.

Severity​

  • INFO
  • WARNING

Code​

  • CreateConstraint
  • CreateIndex
  • CreateStream
  • CheckStream
  • CreateTrigger
  • DropConstraint
  • DropReplica
  • DropIndex
  • DropStream
  • DropTrigger
  • ConstraintAlreadyExists
  • IndexAlreadyExists
  • LoadCSVTip
  • IndexDoesNotExist
  • ConstraintDoesNotExist
  • RegisterReplica
  • ReplicaPortWarning
  • SetReplica
  • StartStream
  • StartAllStreams
  • StopStream
  • StopAllStreams