[IGNITE-9269] Stall optimistic transactions reads if there is a candidate for PREPARED transaction

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: general
• Ignite Flags: Docs Required
• Assignee: Unassigned
• Reporter: Alexey Goncharuk
• Created: 14/Aug/18 15:41
• Updated: 14/Aug/18 15:41

Description

This is an idea that needs confirmation and accurate benchmarking.

Currently, when a read is performed inside an optimistic serializable transaction, we capture the value and entry version immediately regardless of the pending transactional locks for the read entry.
If there is a write candidate on the entry, this scenario will very likely result in optimistic write conflict exception. If a read observes a single (or several?) write candidates on the entry, we may stall the read until the pending prepared transaction is committed and proceed with the read only later. This is a speculative optimization, but it may reduce the chance of getting optimistic write conflict exception.