Add a perf-importent Notification index

[MikeAlhayek]

When user have lots of notifications, there is a significant degrade is query performance. This index is important to improve the speed of the notification queries used by OC

[hishamco]

Is the index used somewhere else?

[MikeAlhayek]

This add a SQL index not SQL Table. This index will be used by multiple queries to improve SQL performance.

CREATE INDEX IDX_NotificationIndex_UserId ON [Notification_NotificationIndex](DocumentId,UserId,IsRead,CreatedAtUtc)

[MikeAlhayek]

@hishamco unless you see an issue with the PR, please approve.

[hishamco]

Sure, I just added a comment waiting for a use case for your index, I'm not sure if it's good to add something without using it in the framework

[MikeAlhayek]

I did explain #16590 (comment) and you replaied with 👍 . This new index will be used by the database server to optimize queries that are generated by the framework.

[gvkries]

Interesting, thanks for the explanation.

[MikeAlhayek]

@gvkries
FYI: When SQL engines select an index, they prioritize included columns from left to right. The new index is likely to be used when querying by DocumentId and UserId, or by DocumentId, UserId, and IsRead, or by DocumentId, UserId, and CreatedAtUtc. Columns on the right can be optional, but including them increases the likelihood that the index will be selected for a query.

[gvkries]

Just a follow-up question: What about the Content column, isn't that probably too large for an index anyway?

[MikeAlhayek]

It is large, but just under the limits. Check out the comments for the column length

OrchardCore/src/OrchardCore/OrchardCore.Notifications.Core/NotificationConstants.cs

Lines 7 to 13 in 51f24d7

	// Maximum length that MySql can support in an inner index under utf8mb4 collation is 768,
	// minus 2 for the 'DocumentId' integer (bigint size = 8 bytes = 2 character size),
	// minus 2 for the 'CreatedAtUtc' (date time size = 8 bytes = 2 character size),
	// minus 26 for 'NotificationId', 26 for 'UserId' and 1 for the 'IsRead' bool,
	// minus 4 to allow a new integer column, for example the 'Id' column,
	// minus 2 to allow a new date time, for example 'ReadAtUtc'.
	public const int NotificationIndexContentLength = 705;

[gvkries]

I should have looked at the source first 🙈 Thank you.

[MikeAlhayek]

@hishamco anything to add here or can we merge it?

[hishamco]

@hishamco anything to add here or can we merge it?

Thanks for the explanation