HTAP

[nikvas0]

At the moment, transactions between OLAP, OLTP, and topics are not working due to different approaches to working with the arbiter. OLTP tables receive the arbiter from the QP and use it, but this is only possible for volatile transactions. OLAP tables ignore the KQP arbiter and use their own. Topics can't use the arbiter at all. OLTP and topics can already work together (commit without an arbiter), so the issue only affects transactions involving OLAP tables.

To solve this problem, we propose using the KQP arbiter for all OLAP table transactions. This would require the following changes:

• Columnshards should use the arbiter selected by the QP (instead of their own).
• Datashards should support an arbiter for non-volatile transactions (since OLAP tables cannot perform volatile transactions).
• Topics should be able to commit using the arbiter. (Only datashard or columnshard can be arbiter.)
• Query Processor should always choose arbiter if OLAP table is present in transaction.