Datastore Statistics is an experimental, innovative, and rapidly changing new feature for Google App Engine. Unfortunately, being on the bleeding edge means that we may make backwards-incompatible changes to Datastore Statistics. We will inform the community when this feature is no longer experimental.
The Administration Console includes a page that shows you statistics for entities in your app's Datastore, as well as statistics for the built-in and composite indexes. To see this page, click Statistics on the left side, under Datastore. The Statistics page displays your data in various ways:
- A pie chart that shows datastore space used by each property type (string, double, blob, etc.).
- Another pie chart showing datastore space by entity kind.
- A textual list next to the pie charts that gives the total space used by each property type.
- A text display above the pie charts showing total size, average size, entry count, and the size of built-in and composite indexes.
By default, the pie charts display statistics for all entities. You can restrict the pie charts to a particular entity kind by choosing from the drop-down menu. The "Metadata" property type represents space consumed by storing properties inside an entry that is not used by the properties directly. The "Datastore Stats" entity, if any, shows the space consumed by the statistics data itself in your datastore.
The statistics data is stored in your app's datastore. To make sure there's room for your app's data, Google App Engine will only store statistics if they consume less than 10 megabytes if namespaces are not used, or 20 megabytes if namespaces are used. If your app's stats go over the limit, kind-specific stats are not emitted. If subsequently these "non-kind" stats exceed the limits, then no stats are updated until stats storage drops below the size limitation. (Any previously reported statistics will remain.) You can determine whether this is happening by looking at the timestamps on stat records. If the timestamp gets older than 2 days, and stats in other applications are being updated regularly then this can indicate that you have run into stat storage size limits for your app.
The space consumed by the statistics data increases in proportion to the number of different entity kinds and property types used by your app. The more different entities and properties used by your app, the more likely you are to reach the stat storage limit. Also, if you use namespaces, remember that each namespace contains a complete copy of the stats for that namespace.
Note: Datastore operations generated by Datastore Statistics count against your application quota.