Add wiki documentation about index.yaml

Index.yaml-Explanation.md

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+# Index Configuration with index.yaml in Google App Engine
+## Overview
+In Google App Engine (GAE), the index.yaml file plays a critical role in managing the indexing of data stored in Datastore, which is essential for executing queries efficiently. This document explains the purpose of index.yaml, why it is important, and provides a guide on how to set up and use this file for a Google App Engine project.
+
+## What is index.yaml?
+index.yaml is a configuration file used in Google App Engine applications to define custom indexes for Datastore. Datastore uses indexes for querying data. Each index powers a specific query type by storing some subset of the data in an efficient way. The index.yaml file specifies which data properties should be indexed, allowing you to tailor the indexes according to the query requirements of your application.
+
+## Why is index.yaml Important?
+**_Query Efficiency:_** Without proper indexes, Datastore queries can be slow and costly, especially as the volume of data grows. Efficient indexing is crucial for performance optimization.<br><br>
+**_Query Capability:_** Certain queries, such as those involving multiple properties or filters and sorting operations, require composite indexes. These indexes need to be explicitly defined in index.yaml.<br><br>
+**_Control and Optimization:_** Managing your indexes via index.yaml provides you with control over index creation and helps optimize datastore usage and costs. Indexes consume storage and having unnecessary indexes can increase costs.<br><br>
+**_Deployment Management:_** index.yaml allows for consistent index configurations across different environments (development, staging, production), ensuring that all environments can successfully execute the same queries.<br><br>
+
+## Breakdown of Index Definitions
+index.yaml has a single list element called indexes. Each element in the list represents an index for the application.<br>
+
+An index element can have the following elements:<br><br>
+**_kind:_**<br>
+&nbsp;&nbsp;Required. The kind of the entity for the query.<br><br>
+**_properties:_**<br>
+&nbsp;&nbsp;A list of properties to include as columns of the index.<br>
+&nbsp;&nbsp;In the order to be sorted: properties used in equality filters first, followed by the property used in inequality filters, then the sort orders.<br><br>
+&nbsp;&nbsp;&nbsp;&nbsp;Each element in this list has the following elements:<br><br>
+&nbsp;&nbsp;&nbsp;&nbsp;**_name:_**<br>
+&nbsp;&nbsp;&nbsp;&nbsp;The datastore name of the property.<br><br>
+&nbsp;&nbsp;&nbsp;&nbsp;**_direction:_**<br>
+&nbsp;&nbsp;&nbsp;&nbsp;The direction to sort, either asc for ascending or desc for descending<br>
+&nbsp;&nbsp;&nbsp;&nbsp;This is only required for properties used in sort orders of the query, and must match the direction used by the query.<br>
+&nbsp;&nbsp;&nbsp;&nbsp;The default is asc.<br><br>
+&nbsp;&nbsp;&nbsp;&nbsp;**_ancestor:_**<br>
+&nbsp;&nbsp;&nbsp;&nbsp;yes if the query has an ancestor clause (either Query.ancestor() or a GQL ANCESTOR IS clause). The default is no.
+
+## Setting Up index.yaml
+
+### 1. Create or Update index.yaml:
+If you are starting a new project, you may not yet have an index.yaml file. Here’s how to create one:<br><br>
+In the root of your project directory (where app.yaml resides), create a file named index.yaml.<br>
+Define the indexes needed for your queries.<br>
+Here is a simple example of what entries in index.yaml might look like:<br><br>
+
+indexes:
+- kind: Product<br>
+  properties:<br>
+  - name: price<br>
+
+- kind: Product<br>
+  properties:<br>
+  - name: category<br>
+    direction: asc<br>
+  - name: price<br>
+    direction: desc<br>
+
+### 2. Deploy index.yaml:
+To deploy the indexes to Google App Engine run command: gcloud app deploy index.yaml<br>
+
+This command will create or update indexes in your Google Cloud project. It’s important to note that index creation can take some time depending on the size of the data.<br><br>
+
+### 3. Automated Index Management:
+When you run your application locally using the development server, App Engine can automatically add required indexes to your index.yaml file based on the queries it encounters. This can be a useful way to ensure all required indexes are defined.<br><br>
+
+### 4. Best Practices
+**_Review and Optimize:_** Regularly review your indexes and query patterns. Remove unnecessary indexes to reduce storage costs.<br><br>
+**_Use Automatic Indexing in Development:_** Allow App Engine to automatically update your index.yaml during development to catch all necessary indexes.<br><br>
+**_Version Control:_** Include index.yaml in your version control system to track changes and ensure consistency across deployments.<br>
+
+# Conclusion
+Managing indexes through index.yaml in Google App Engine is crucial for both performance and cost management. By carefully defining and maintaining your indexes, you ensure that your application remains efficient and capable of handling complex queries as it scales.