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Frankjia-7984 avatar image
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Frankjia-7984 asked GeethaThatipatri-MSFT commented

For Azure SQL Business critial edition, what's the data latency in between primary & 2ndary replicas?

Hi There,

I have a quick question regarding to the data latency concerns for Azure SQL Server Business Critical edition

From below MS official doc (https://docs.microsoft.com/en-us/azure/azure-sql/database/service-tier-hyperscale-named-replicas-faq#how-much-delay-is-there-between-the-primary-and-secondary-compute-replicas-), for hyperscale edition, the doc says:
"...Typical data latency for small transactions is in tens of milliseconds, however there is no upper bound on data latency. ..."

I was wondering if I upgrad to Azure SQL Business Critical Edition, do I need to worry about data latency concerns between primary replica and secondary replicas? if the latency is less than dozens of milliseconds, then it's fine for our business.

thanks in advance,
Frank

cc @Oury Ba-MSFT @maurid



azure-sql-database
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for Azure SQL HyperScale edition, below SLA cann't meet our business requirement:
"there is no upper bound on data latency." so we have to think of upgrading to Business Critial Edition



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1 Answer

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GeethaThatipatri-MSFT answered GeethaThatipatri-MSFT commented

Hi, @Frankjia-7984 Welcome to Microsoft Q&A, Thanks for posting your query.
As we understand the ask here is you want to know for Business-critical if there is latency in between primary & 2ndary replicas?.

The document which you are referring to is for Hyperscale, For HA (local nodes) we ensure the data is persisted to at least one other node before committing the transaction you can refer to more information here.
Can you please elaborate on the business scenario that requires data latency between two geo-locations to be “less than dozens of milliseconds?
I would like to know if you are concerned with replication to the local HA copies or if you are using geo-replication since there are some differences there. if you are using geo-replication in the BC tier we have some information related to the RPO in the SLAs
193195-image.png Please refer here

The latency between primary and secondary for HA replicas for BC and hyper scale tiers tend to both be on the order of a few milliseconds

Regards
Geetha






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Hi Geetha,
thanks for the quick response. here is my scenarios:
presently we use Azure SQL Server Hyperscale edition, we can not read the data back ~100milliseconds after the data was write to DB; I checked Azure SQL Server HyperScale officical docs, it states that "...there is no upper bound on data latency.."
With this being the fact, we are thinking of migrating to Azure SQL Server Business Critical Edition.
Now we concern was:
What is the data latency between Primary Replica & those Read Replicas?
Say I wrote DataXYZ to Primary Replica,
50ms later, can I read DataXYZ back successfully without worrying about data latency issue between this write and read actions?







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"I would like to know if you are concerned with replication to the local HA copies or if you are using geo-replication since there are some differences there."

  • we only concern with the replication to the Local HA copies for now. I think if we try to avoid the scenario of submitting the batch and then fetch them immediately, it would work as we expect.

thanks again Geetha.
Frank

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Thanks, @Frankjia-7984 · for your feedback! and for visiting Microsoft QA forums! Have a great day!

Regards
Geetha

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