MDEV-32823 Sequences may diverge with Galera #363
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This patch improves support for SEQUENCEs when used with Galera. The original ticket, MDEV-28971, comes with a test case showing that the combination SEQUENCES do not work in combination with Galera's streaming replication. To fix that, it is necessary to include the contents of stmt cache when preparing a fragment for replication. Additional testing showed that support for SEQUENCEs is broken, even for regular transactions replicated through Galera. Galera did not correctly implement the non-transactional semantics of SEQUENCEs. For instance: ``` BEGIN; INSERT INTO some_table VALUES(...) SELECT NEXTVAL(s); ROLLBACK; ``` should result in the `INSERT` to be rolled back, while the value consumed SEQUENCE `s` by `NEXTVAL(s)`, can't be rolled back and must be committed. This is problematic for Galera, as ROLLBACK results in no writeset. Therefore, transactions that rollback voluntarily rollback, or are rolled back due to cluster-wide conflicts, result in SEQUENCEs that diverge throughout the cluster. Also, when binlogs are enabled, those diverge too. To fix this, we replicate the contents statment cache whenever a value from a sequence is consumed. Allowing ROLLBACK to undo transactional changes, while preserving the changes made to the SEQUENCEs.
Move replication from SEQUENCE::next_value() to ha_sequence::write_row(). This has the following benefits: 1. We get replication of sequence SETVAL(), which was not working 2. In write_row(), first the pending row event is generated, and replicated before the row is written to storage engine. Should replication fail, we get rid of the pending row event and return the error. Added tests for BF aborts, and a test that shows nodes can recover sequence operations through IST (even after certification failure).
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