This great article provides a performance comparison between the different Azure SQL Database performance tiers. Notably in his tests
the read performance of 1 DTU in Premium Tier is about 10x the read performance of 1 DTU in Standard Tier, while the write performance, CPU, and memory appear to be about the same between Standard and Premium
per DTU (*).
(* = except for the anomaly that S3 was worse than S2, which he assumed was a bug that'd be soon fixed.)
Questions:
- Is that disparity between standard and premium DTUs published/intended by Microsoft?
- Is there any disparity between the performance of elastic DTUs vs non-elastic DTUs (if you assume there's only one database active in an elastic pool)? e.g. will a 100-DTU standard pool with 1 db perform exactly the same as a S3 database?
The reason behind my questions is we're migrating around 30 databases from Web/Business to new service tiers and trying to get similar performance as with Web/Business. Currently we have a Standard elastic pool
but the max DTU per database of 100 means we're not getting sufficient throughput and encounter a lot of timeouts.
I can increase the pool to 200 DTUs but our load is intermittent and generally there's only one database active at a time so that's not going to help much. If I swap to a Premium pool I can get 125 DTUs = 1.25x
performance for ~3x the price, (factoring in the 50% preview discount) or 250 DTUs = 2.5x performance at ~6x price of standard. I know premium offers other high availability benefits for that additional cost but for my purposes I'm only interested in increased
performance.
If 1 premium DTU is known to be better than 1 standard DTU then maybe the performance of a premium 125 DTU pool will be more than 1.25x a standard 100 DTU pool, so maybe I can justify the increased price. But
if that disparity between standard and premium DTU is an anomaly that might be corrected later then I'm hesitant to rely on that.
thanks!
Rory
