This is a snapshot of the documentation for AppEngine NDB. If you want to read old, possibly obsolete documentation, feel free!

Google App Engine

NDB Administration

There are tools and APIs to make it easier to administer an application's stored data.

Administration Console

When using the Administration Console, remember that NDB is implemented by means of the Datastore and memcache. When NDB "reads" a value, it checks memcache first; it only reads from the Datastore if it doesn't find the value in memcache.

Thus, if you use the Administration console to edit an entity Datastore, the application may still use the "old" value if that value is in memcache. You might work around this by purging memcache. This is rather disruptive, however; if you need to tweak values "by hand" often, you might want to set up a UI for this in your application that writes values via the NDB API; writing via NDB keeps the Datastore and memcache in sync.

Metadata Queries

NDB supports a metadata query API. This allows an application to get some general information about its Datastore. This API is in the google.appengine.ext.ndb.metadata module. It has functions:

  • get_namespaces(start=None, end=None): return a list of namespace names
  • get_kinds(start=None, end=None): return a list of kind names
  • get_properties_of_kind(kind, start=None, end=None): return a list of property names for the given kind name
  • get_representations_of_kind(kind, start=None, end=None): return a dict mapping property names for the given kind name to lists of representation names such as 'STRING', 'BOOLEAN' or 'INT64'.

These functions have optional start and end arguments that can be used to restrict the query to a certain range. Here, start is inclusive and end is exclusive. Both default to None. For example, to get all namespaces starting with a lowercase letter you could call get_namespaces('a', chr(ord('z') + 1)). All of these except get_namespaces() are implicitly restricted to the current namespace. Beware of the cost of metadata queries.

Statistics Queries

The datastore maintains statistics about the data stored for an application, such as how many entities there are of a given kind, or how much space is used by property values of a given type. You can view these statistics in the Administration Console, under Datastore > Statistics.

You can also access these values programmatically within the application by querying for specially named entites using the datastore API. Each statistic is accessible as an entity whose kind name begins and ends with two underscores. For example, each app has exactly one entity of the kind __Stat_Total__ that represents statistics about all of the entities in the datastore in total. Each statistic entity has the following properties:

  • count, the number of items considered by the statistic (a long integer)
  • bytes, the total size of the items for this statistic (a long integer)
  • timestamp, the time of the most recent update to the statistic (a date-time value)

Some statistic kinds also have additional properties, listed below.

An application can use model classes provided by the package google.appengine.ext.ndb.stats to access statistic entities.

from google.appengine.ext.ndb import stats

global_stat = stats.GlobalStat.query().get()
print 'Total bytes stored: %d' % global_stat.bytes
print 'Total entities stored: %d' % global_stat.count

When the statistics system creates new statistic entities, it does not delete the old ones right away. The best way to get a consistent view of the statistics is to query for the GlobalStat entity with the most recent timestamp, then use that timestamp value as a filter when fetching other statistic entities.

The statistic entities are included in the calculated statistic values. Statistic entities take up space relative to the number of unique kinds and property names used by the application.

The statistics system will also create statistics specific to each namespace. Note that if an application does not use datastore namespaces then namespace specific statistics will not be created. Namespace specific stats are found in the namespace that they're specific to. The kind names for namespace specific stats are prefixed with __Stat_Ns_ and have the same corresponding suffix as application wide statistics kinds.

The complete list of available statistics is as follows:

Statistic Stat Entity Kind Description
all entities __Stat_Total__
Python class: GlobalStat

Namespace specific entry:
__Stat_Ns_Total__
Python class: NamespaceGlobalStat

 All entities. Additional properties:
  • entity_bytes: The storage in the entities table measured in bytes.
  • builtin_index_bytes: The storage in built-in index entries measured in bytes.
  • builtin_index_count: the count of built-in index entries.
  • composite_index_bytes: The storage in composite index entries measured in bytes.
  • composite_index_count: The count of composite index entries.
all entities in a namespace __Stat_Namespace__
Python class: NamespaceStat

Note that __Stat_Namespace__ entities are created for each namespace encountered and are only found in the empty string namespace.

All entities in a namespace.

  • subject_namespace, the namespace represented (a string)
  • entity_bytes: The storage in the entities table measured in bytes.
  • builtin_index_bytes: The storage in built-in index entries measured in bytes.
  • builtin_index_count: the count of built-in index entries.
  • composite_index_bytes: The storage in composite index entries measured in bytes.
  • composite_index_count: The count of composite index entries.
all entries in application defined indexes __Stat_Kind_CompositeIndex__

Namespace specific entry: __Stat_Ns_Kind_CompositeIndex__


Python class: KindStat

Namespace specific entry:
__Stat_Ns_Kind__
Python class: NamespaceKindStat

 Entries in the composite index table; one stat entity for each kind of entity stored. Additional properties:
  • index_id, the index id.
  • kind_name, the name of the kind represented (a string)
entities of a kind __Stat_Kind__
Python class: KindStat

Namespace specific entry:
__Stat_Ns_Kind__
Python class: NamespaceKindStat

 Entities of a kind; one stat entity for each kind of entity stored. Additional properties:
  • kind_name, the name of the kind represented (a string)
  • entity_bytes: The storage in the entities table measured in bytes.
  • builtin_index_bytes: The storage in built-in index entries measured in bytes.
  • builtin_index_count: the count of built-in index entries.
  • composite_index_bytes: The storage in composite index entries measured in bytes.
  • composite_index_count: The count of composite index entries.
root entities of a kind __Stat_Kind_IsRootEntity__
Python class: KindRootEntityStat

Namespace specific entry:
__Stat_Ns_Kind_IsRootEntity__
Python class: NamespaceKindRootEntityStat

Entities of a kind that are entity group root entities (have no ancestor parent); one stat entity for each kind of entity stored. Additional properties:

  • kind_name, the name of the kind represented (a string)
  • entity_bytes: The storage in the entities table measured in bytes.
non-root entities of a kind __Stat_Kind_NotRootEntity__
Python class: KindNotRootEntityStat

Namespace specific entry:
__Stat_Ns_Kind_NotRootEntity__
Python class: NamespaceKindNotRootEntityStat

Entities of a kind that are not entity group root entities (have an ancestor parent); one stat entity for each kind of entity stored. Additional properties:

  • kind_name, the name of the kind represented (a string)
  • entity_bytes: The storage in the entities table measured in bytes.
properties of a type __Stat_PropertyType__
Python class: PropertyTypeStat

Namespace specific entry:
__Stat_Ns_PropertyType__
Python class: NamespacePropertyTypeStat

Properties of a value type across all entities; one stat entity per value type. Additional properties:

  • property_type, the name of the value type (a string)
  • entity_bytes: The storage in the entities table measured in bytes.
  • builtin_index_bytes: The storage in built-in index entries measured in bytes.
  • builtin_index_count: the count of built-in index entries.
properties of a type per kind __Stat_PropertyType_Kind__
Python class: KindPropertyTypeStat

Namespace specific entry:
__Stat_Ns_PropertyType_Kind__
Python class: NamespaceKindPropertyTypeStat

Properties of a value type across entities of a given kind; one stat entity per combination of property type and kind. Additional properties:

  • property_type, the name of the value type (a string)
  • kind_name, the name of the kind represented (a string)
  • entity_bytes: The storage in the entities table measured in bytes.
  • builtin_index_bytes: The storage in the built-in index measured in bytes.
  • builtin_index_count: the count of built-in index entries.
properties with a name __Stat_PropertyName_Kind__
Python class: KindPropertyNameStat

Namespace specific entry:
__Stat_Ns_PropertyName_Kind__
Python class: NamespaceKindPropertyNameStat

Properties with a given name across entities of a given kind; one stat entity per combination of unique property name and kind. Additional properties:

  • property_name, the name of the property (a string)
  • kind_name, the name of the kind represented (a string)
  • entity_bytes: The storage in the entities table measured in bytes.
  • builtin_index_bytes: The storage in built-in index entries measured in bytes.
  • builtin_index_count: the count of built-in index entries.
properties of a type and with a name __Stat_PropertyType_PropertyName_Kind__
Python class: KindPropertyNamePropertyTypeStat

Namespace specific entry:
__Stat_Ns_PropertyType_PropertyName_Kind__
Python class: NamespaceKindPropertyNamePropertyTypeStat

Properties with a given name and of a given value type across entities of a given kind; one stat entity per combination of property name, value type and kind that exists in the datastore. Additional properties:

  • property_type, the name of the value type (a string)
  • property_name, the name of the property (a string)
  • kind_name, the name of the kind represented (a string)
  • entity_bytes: The storage in the entities table measured in bytes.
  • builtin_index_bytes: The storage in built-in index entries measured in bytes.
  • builtin_index_count: the count of built-in index entries.

Some statistics refer to datastore property value types by name, as strings. These names are as follows:

  • "Blob"
  • "BlobKey"
  • "Boolean"
  • "Category"
  • "Date/Time"
  • "Email"
  • "Float"
  • "GeoPt"
  • "IM"
  • "Integer"
  • "Key"
  • "Link"
  • "NULL"
  • "PhoneNumber"
  • "PostalAddress"
  • "Rating"
  • "ShortBlob"
  • "String"
  • "Text"
  • "User"

Note that __Stat_Namespace__ entities contain the same information found in __Stat_Ns_Total__ records. __State_Namespace__ entities are stored in the empty namespace and contain a subject_namespace field describing the namespace to which they belong. __Stat_Ns_Total__ records are stored in the namespace to which they refer, and thus do not contain a subject_namespace field. Hence, a query on kind __Stat_Namespace__ (from the empty string namespace) ordered descending by bytes will list the namespaces that consume the largest storage first. Since queries across namespaces are not possible, any query for __State_Ns_Total__ entities will only ever produce at most single record.

Authentication required

You need to be signed in with Google+ to do that.

Signing you in...

Google Developers needs your permission to do that.