Percona 8.0 innodb early lock release problem

MySQL & MariaDB Percona Server for MySQL 8.0
1 
    trx_release_impl_and_expl_locks(trx, serialised);

    ... 

    lsn_t lsn = mtr->commit_lsn();

    if (lsn == 0) {
      /* Nothing to be done. */
    } else if (trx->flush_log_later) {
      /* Do nothing yet */
      trx->must_flush_log_later = true;

      /* Remember current ddl_operation, because trx_init()
      later will set ddl_operation to false. And the final
      flush is even later. */
      trx->ddl_must_flush = trx->ddl_operation;
    } else if ((srv_flush_log_at_trx_commit == 0 ||
                thd_requested_durability(trx->mysql_thd) ==
                    HA_IGNORE_DURABILITY) &&
               (!trx->ddl_operation)) {
      /* Do nothing */
    } else {
      trx_flush_log_if_needed(lsn, trx);
    }

    trx->commit_lsn = lsn;

In innodb, trx will release lock before flush redo log into disk. If T1 release lock before log flushing, T2 can read the modification of T1. There is a crash before T1 flushing log. T2 may return incorrect result to client before crash. Because the redo log of T1 can’t found on disk and T1 can’t be recoverd.

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2

you’re likely looking at the ‘else if’ condition:

srv_flush_log_at_trx_commit == 0

This is kind of the expected behavior with reduced durability. There are other known side effects of reduced durability like replica being ahead of their source.

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