Is sp_send_dbmail with #query param synchronous - sql-server

Question

Let's imagine that I have a table ExchangeSession with field Processed.
I need to send e-mail with all ExchangeSession with Processed = 0 and then update these sessions to Processed = 1. Like this:
EXEC msdb.dbo.sp_send_dbmail
#profile_name = 'SomeProfile',
#recipients='SomeAddress',
#subject = 'SomeSubject',
#body = #bodyparam,
#body_format = 'TEXT',
#query = N'SET NOCOUNT ON; select * from ExchangeSession where Processed = 0',
#execute_query_database = #dbnameparam,
#attach_query_result_as_file = 1,
#query_attachment_filename = 'report.csv',
#query_result_header = 1,
#query_result_width = 32767,
#query_result_separator = #delimiterparam,
#exclude_query_output = 1,
#append_query_error = 0,
#query_no_truncate = 0,
#query_result_no_padding = 1;
update ExchangeSession
set
Processed = 1
where
Processed = 0
Will sp_send_dbmail executes my query synchronously relatively to the batch or asynchronously? In other words is there any chance that in the e-mail I'll not get all unprocessed sessions?

Answer 1

The answer is YES. query param execution is synchronous relatively to the batch.
Made the following test:
insert dbo.[CallLog]([Name]) values ('BeforeMail')
set #queryparam = N'SET NOCOUNT ON;
insert dbo.[CallLog]([Name]) values (''Attachment'');
SELECT
0 as [ID],
...'
...
EXEC msdb.dbo.sp_send_dbmail
...
#query = #queryparam,
...
insert dbo.[CallLog]([Name]) values ('AfterMail')
And voila, the results in CallLog:
LogID Name
801 BeforeMail
802 Attachment
803 AfterMail
Also I looked at sysmail_allitems and sysmail_mailattachments. The send_request_date value in the sysmail_allitems is exactly the same as last_mod_date value in the sysmail_mailattachments.
And the value of sent_date in the sysmail_allitems slightly differs.
So sp_send_dbmail executes the query synchronously in the batch, saves results into a file and then later on send an e-mail.

Answer 2

I am not 100% certain, but I would assume that it is possible that new entries could sneak into your ExchangeSession table between sending the email and updating the records. I would play safe by doing:
update ExchangeSession
set Processed = 2 -- This procedure should be the only place that sets Processed to 2
where Processed = 0
EXEC msdb.dbo.sp_send_dbmail
....
#query = N'SET NOCOUNT ON; select * from ExchangeSession where Processed = 2',
....
update ExchangeSession
set Processed = 1
where Processed = 2