Support Azure AI Search Sticky Sessions

[alexmg]

Motivation and Context (Why the change? What's the scenario?)

The UseSessionId property on the SearchOptions can help improve the relevance of search results when multiple replicas are configured. This should be the case in any production deployment as two replicas are required for high availability of read-only workloads (queries), and three or more for high availability of read-write workloads (queries and indexing).

A value to be used to create a sticky session, which can help getting more consistent results. As long as the same sessionId is used, a best-effort attempt will be made to target the same replica set. Be wary that reusing the same sessionID values repeatedly can interfere with the load balancing of the requests across replicas and adversely affect the performance of the search service. The value used as sessionId cannot start with a '_' character.

https://learn.microsoft.com/en-us/rest/api/searchservice/documents/search-post?view=rest-searchservice-2024-07-01&tabs=HTTP#request-body

Using this setting should also provide more consistent results from the AzureAISearchMemory.GetListAsync method. Without an orderby parameter results are sorted by score, and when * is used as the search query, all results have the same score of 1. This increases the likelihood of getting inconsistent results when the search query hits different replicas.

High level description (Approach, Design)

Extend the AzureAISearchConfig class with a new UseSessionId property:

• Default the setting to false to avoid any change in behaviour for existing users and to make its use an explicit choice like UseHybridSearch
• Rename the DefineFieldsToSelect method in AzureAISearchMemory to ApplyCommonSearchOptions as it will be used to also apply the UseSessionId setting
• When the setting is true set the SessionId property on the SearchOptions to Guid.NewGuid().ToString("N") ensuring the same session ID is used while paging results but is not reused for subsequent method calls
• Take the opportunity to remove duplicate code present for setting the SearchOptions.Filter property by passing the ICollection<MemoryFilter>? to the ApplyCommonSearchOptions method
• Update the interactive setup to include a question to set the UseSessionId property
• Include the new setting with comment in the various appsettings.json files in the solution

[dluc]

Nice add!