Slow down execution of bulk inserts - asp.net

Question

We have an Azure SQL database which is on the S1 pricing tier. Our site is extremely heavily cached, so database hits are absolutely minimal. Average DTU usage is only ~1.5%, this is great as our DB costs are a fraction of what they used to be on our old website (£20p/m vs £400 p/m!)
On the site however, we do have small scripts that require insertion of ~100k records or so (user notifications for when someone performs an action such as creates a new tutorial).
When this is triggered, DTU's spike at 100% for around 3-5 minutes.
The script is simply a loop which calls an insert:
using(var db = new DBContext())
{
foreach(var userID in userIDs)
{
db.ExecuteCommand(
"INSERT INTO UserNotifications " +
"(ForUserID, Date, ForObjectTypeID, ForObjectID, TypeID, Count, MetaData1)
VALUES ({0}, {1}, NULL, {2}, {3}, {4}, {5}, {6})",
userID, DateTime.Now.ToUniversalTime(), forObjectID, (byte)type, 1, metaData1.Value
);
}
}
Is there a faster way to do inserts than this?
Additionally, what would be the best way to slow down execution of this script so DTU usage doesn't choke everything up?

Answer 1

You are doing one row per insert - that is not efficient.
A TVP is a like a reverse datareader and is efficient.
Lower tech is to insert 900 rows at a time (1000 is the max). This alone is probably 400x more efficient.
StringBuilder sb = new StringBuilder();
string insert = "INSERT INTO UserNotifications " +
"(ForUserID, Date, ForObjectTypeID, ForObjectID, TypeID, Count, MetaData1) " +
"VALUES ";
sb.AppendLine(insert);
int count = 0;
using(var db = new DBContext())
{
foreach(var userID in userIDs)
{
sb.AppendLine(string.Format(({0}, {1}, NULL, {2}, {3}, {4}, {5}, {6}), ",
userID, DateTime.Now.ToUniversalTime(), forObjectID, (byte)type, 1, metaData1.Value);
count++;
if (count = 990)
{
db.ExecuteCommand(sb.ToString());
count = 0;
sb.Clear();
sb.AppendLine(insert);
//can sleep here to throttle down cpu
}
}
if (count > 0)
{
db.ExecuteCommand(sb.ToString());
}
}

Answer 2

Instead of insert entity by entity you can make an insert of 100 entities at the same time packing the entities in a JSON and writing a store procedure that use it like in this example:
INSERT INTO [dbo].[AISecurityLogs]
([IpAddress], [TimeRange], [Requests], [LogId])
SELECT *, LogId = #logId
FROM OPENJSON ( #json )
WITH (
IpAddress varchar(15) '$.IpAddress',
TimeRange DATETIME '$.TimeRange',
Requests int '$.Requests'
)
To slow down execution and doesn't lost anything you can put the logs in a queue, and then read this information with an azure Job, that allow you to configure the read interval, and insert in the database as I wrote before.
This approach allows a big load (I have some several in production environments) and if something goes wrong with the agent or with the database, the messages are stored in the queue until you move them to the database.