Can anybody give an example or scenario of log sequence number(LSN) used in MySQL
Log Sequence Number (LSN) : Log Sequence Numbers correspond to given position in the log files and typically incremented for each log record. Innodb uses number of bytes ever written to the log files however it could be something different. LSNs are often extensively used in recovery check pointing and buffer management operations. When checkpoint (both fuzzy and not) happens you get something like “all changes up to LSN=X are now flushed to the data space” this means you can discard or archive logs for LSN earlier than that. When doing log recovery checking LSN in the log record can tell if you this change needs to be applied or it already was applied (when doing recovery you do not know which dirty pages were flushed from the buffer pool).
The LSN do not relate much to transactions – changes from different transactions are intermixed in the log files and many LSNs can correspond to changes from the same transaction.
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