Igor Seliverstov created IGNITE-11173:
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Summary: MVCC TX: Acquire write version if coordinator changed in
the middle of tx.
Key: IGNITE-11173
URL: https://issues.apache.org/jira/browse/IGNITE-11173
Project: Ignite
Issue Type: New Feature
Components: mvcc
Reporter: Igor Seliverstov
Current implementation suppose all transactions on previous coordinator were
finished before new coordinator has been initialized, but there is a case when
it isn't true.
A tx which hasn't obtained a topology lock (hasn't done any updates) doesn't
prevent a topology change, this way nothing prevent new transactions start.
All newly created txs suppose all updates on previous coordinator are finished
- this mean a possible update of mapped on previous coordinator txs is
considered as stale regardless the tx is still active. We make such txs
readonly to not break the visibility checking logic (see IGNITE-8841).
There are two possible ways to allow writes after coordinator is changed:
* collect active txs and their dependencies and populate the active txs list
with them during a new coordinator initialization - this approach is quite
complex and have obvious issues like necessity of using full tx versions in a
snapshot
* acquire a new version right after topology locked for writes using previously
acquired "read" version for possible write conflicts detecting and visibility
checking.
I would prefer the second option as fully understandable and relatively easy to
implement.
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