score:0
you could put the contents of your csv list objects into a table value parameter. then call a stored procedure, passing in that tvp. the stored procedure could then run a cursor through the 300 databases and joins to your table value parameter (using ad-hoc sql). it will basically be a loop that iterates 300 times which isn't too bad. something like this:
create procedure yournewprocedure
(
@tablevalueparameter dbo.udttvp readonly
)
as
declare @dbname varchar(255)
declare @sql nvarchar(3000)
declare db_cursor cursor local for
select distinct name
from sys.databases
where name like '%yourdbs%'
open db_cursor
fetch next from db_cursor into @dbname
while @@fetch_status = 0
begin
set @sql = 'update t
set t2.field = t.field
from @tablevalueparameter t
join [' + @dbname + ']..tableyoucareabout t2 on t.field = t2.field '
exec sp_executesql @sql, n'@tablevalueparameter dbo.udttvp', @tablevalueparamete
fetch next from db_cursor into @dbname
end
close db_cursor
deallocate db_cursor
score:1
you seem to have the basic idea right. hitting the database once for every line in the csv is going to be way too slow. you can create a "where in" statement via linq like so:
var addresses = getemailaddresses();
var entries = ctx.entries.where(e => addresses.contains(e.emailaddress));
however, if you have too many addresses in your list, it'll take a long, long time to generate and evaluate your query. i'd recommend splitting your input list up into batches of a reasonable size (200 entries?), and then using the trick above to handle each batch with a single database check.
once you've got that working, you can try a few other things to see if they make a measurable difference performance-wise:
- tweak the batch size.
- run the batches independently with varying degrees of parallelism.
- play with indexes on the database tables, particularly on the email address field.
- order the email addresses before breaking them into batches. it's possible that the db queries will take better advantage of hard disk caching strategies.
Source: stackoverflow.com
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