We run a web service that gets 6k+ requests per minute during peak hours and about 3k requests per minute during off hours. Lots of data feeds compiled from 3rd party web services and custom generated images. Our service and code is mature, we've been running this for years. A lot of work by good developers has gone into our service's code base.
We're migrating to Azure, and we're seeing some serious problems. For one, we are seeing our Premium P1 SQL Azure database routinely become unavailable for 1-2 full entire minutes. I'm sorry, but this seems absurd. How are we supposed to run a web service with requests waiting 2 minutes for access to our database? This is occurring several times a day. It occurs less after switching from Standard level to Premium level, but we're nowhere near our DB's DTU capacity and we're getting throttled hard far too often.
Our SQL Azure DB is Premium P1 and our load according to the new Azure portal is usually under 20% with a couple spikes each hour reaching 50-75%. Of course, we can't even trust Azure's portal metrics. The old portal gives us no data for our SQL, and the new portal is very obviously wrong at times (our DB was not down for 1/2 an hour, like the graph suggests, but it was down for more than 2 full minutes):
Azure reports the size of our DB at a little over 12GB (in our own SQL Server installation, the DB is under 1GB - that's another of many questions, why is it reported as 12GB on Azure?). We've done plenty of tuning over the years and have good indices.
Our service runs on two D4 cloud service instances. Our DB libraries are all implementing retry logic, waiting 2, 4, 8, 16, 32, and then 48 seconds before failing completely. Controllers are all async, most of our various external service calls are async. DB access is still largely synchronous but our heaviest queries are async. We heavily utilize in-memory and Redis caching. The most frequent use of our DB is 1-3 records inserted for each request (those tables are queried only once every 10 minutes to check error levels).
Aside from batching up those request logging inserts, there's really not much more give in our application's db access code. We're nowhere near our DTU allocation on this database, and the server our DB is on has like 2000 DTU's available to be allocated still. If we have to live with 1+ minute periods of unavailability every day, we're going to abandon Azure.
Is this the best we get?
Querying stats in the database seems to show we are nowhere near our resource limits. Also, on premium tier we should be guaranteed our DTU level second-by-second. But, again, we go more than an entire solid minute without being able to get a database connection. What is going on?
I can also say that after we experience one of these longer delays, our stats seem to reset. The above image was a couple minutes before a 1 min+ delay and this is a couple minutes after:
We have been in contact with Azure's technical staff and they confirm this is a bug in their platform that is causing our database to go through failover multiple times a day. They stated they will be deploying fixes starting this week and continuing over the next month.
Frankly, we're having trouble understanding how anyone can reliably run a web service on Azure. Our pool of Websites randomly goes down for a few minutes a few times a month, taking our public sites down. If our cloud service returns too many 500 responses something in front of it is cutting off all traffic and returning 502's (totally undocumented behavior as far as we can tell). SQL Azure has very limited performance and obviously isn't ready for prime time.
来源：https://stackoverflow.com/questions/29083219/sql-azure-premium-tier-is-unavailable-for-more-than-a-minute-at-a-time-and-were