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This API is supported for first-generation runtimes and can be used when upgrading to corresponding second-generation runtimes. If you are updating to the App Engine Python 3 runtime, refer to the migration guide to learn about your migration options for legacy bundled services.There are tools and APIs to make it easier to administer an application's stored data.
Google Cloud consoleWhen using the Google Cloud console, remember that NDB is implemented by means of Datastore and memcache. When NDB "reads" a value, it checks memcache first; it only reads from Datastore if it doesn't find the value in memcache.
Thus, if you use the Google Cloud console to edit an entity in Datastore, the application might 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 client library; writing via NDB keeps Datastore and memcache in sync.
NDB supports a metadata query API. This allows an application to get some general information about its use of 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 namesget_kinds(start=None, end=None): return a list of kind namesget_properties_of_kind(kind, start=None, end=None): return a list of property names for the given kind nameget_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. Metadata gets and queries are billed in the same way as Datastore gets and queries.
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 Google Cloud console, in the Dashboard page.
You can also access these values programmatically within the application by querying for specially named entities 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 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.
Applications with thousands of namespaces, kinds, or property names require a very large number of statistics entities. To keep the overhead of storing and updating the statistics reasonable, Datastore progressively drops statistics entities, in the following order:
__Stat_Ns_PropertyName_Kind__, __Stat_Ns_PropertyType_PropertyName_Kind____Stat_PropertyName_Kind__, __Stat_PropertyType_PropertyName_Kind____Stat_Ns_Kind__, __Stat_Ns_Kind_IsRootEntity__, __Stat_Ns_Kind_NotRootEntity__, __Stat_Ns_PropertyType_Kind____Stat_Kind__, __Stat_Kind_IsRootEntity__, __Stat_Kind_NotRootEntity__, __Stat_PropertyType_Kind____Stat_Namespace__, __Stat_Ns_Kind_CompositeIndex__, __Stat_Ns_PropertyType__, __Stat_Ns_Total__The summary statistics entities (__Stat_Kind_CompositeIndex__, __Stat_PropertyType__, __Stat_Total__) are never dropped.
The complete list of available statistics is as follows:
Statistic Stat Entity Kind Description all entities__Stat_Total__
GlobalStat
__Stat_Ns_Total__
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__
NamespaceStat
__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__
__Stat_Ns_Kind_CompositeIndex__
Python class: KindStat
• index_id, the index id.
kind_name, the name of the kind represented (a string) entities of a kind __Stat_Kind__
KindStat
__Stat_Ns_Kind__
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__
KindRootEntityStat
__Stat_Ns_Kind_IsRootEntity__
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__
KindNotRootEntityStat
__Stat_Ns_Kind_NotRootEntity__
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__
PropertyTypeStat
__Stat_Ns_PropertyType__
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__
KindPropertyTypeStat
__Stat_Ns_PropertyType_Kind__
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__
KindPropertyNameStat
__Stat_Ns_PropertyName_Kind__
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__
KindPropertyNamePropertyTypeStat
__Stat_Ns_PropertyType_PropertyName_Kind__
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 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"__Stat_Namespace__ entities contain the same information found in __Stat_Ns_Total__ records. __Stat_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. Because queries across namespaces are not possible, any query for __Stat_Ns_Total__ entities will only ever produce at most a single record.
Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.
Last updated 2025-08-07 UTC.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-07 UTC."],[[["This API supports first-generation runtimes and can be used when upgrading to corresponding second-generation runtimes, with a migration guide available for the App Engine Python 3 runtime."],["NDB, utilizing both Datastore and memcache, prioritizes memcache for read operations, so edits made directly in the Google Cloud console may not be immediately reflected in the application unless memcache is purged or changes are written via NDB."],["The metadata query API in `google.appengine.ext.ndb.metadata` provides functions like `get_namespaces`, `get_kinds`, `get_properties_of_kind`, and `get_representations_of_kind` to retrieve general information about Datastore usage."],["Datastore statistics, accessible through the Google Cloud console and programmatically using the `google.appengine.ext.ndb.stats` package, offer insights into data storage, entity counts, and space used by property values."],["Datastore's statistics system progressively drops statistics entities in a specific order, starting with the most granular (per-namespace, per-kind, and per-property) to maintain reasonable storage and update overhead."]]],[]]
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