I'm not convinced HTAP can actually work - the they OLTP and OLAP works internally seems too different.
In-Memory HANA is freakishly good for running OLAP BW queries against fresh data. Column stores like HANA and IQ are both good at this, but to be honest, I don’t know how BW systems were typically configured before HANA/IQ.
But we definitely ended up in a situation where it was hard to get to some important data, since the team couldn't SLT it to BW because "it's too many transactions" and trying to get it from Sidecar was blowing up, because it's too much data. And that was already with S/4.
But again, I don't know why it was the case. It would have been great and saved us a lot of work if it worked out and we could've done stuff in HANA directly, instead of copying data to different OLAP system daily. Especially now, when everyone is trying to get on the realtime-train.
TiDB distinguishes itself with HTAP; transparently incorporating OLTP/ETL/OLAP in a single cluster. You have to specify the ETL layer and data warehouse in addition to PostgreSQL to make an apples to apples comparison; that is the core of HTAP positioning.
SAP HANA is the poster child for HTAP, a data warehouse with good enough OLTP performance to replace Oracle RDBMS; a single system is used for both SAP app tiers, Business Suite and Business Warehouse. The same value proposition applies to cloud apps. Independent OLTP/ETL/OLAP is still robust and is more modular while HTAP is more tightly integrated and simpler to operate.