This feature reduces the warm up time by restoring buffer pool state from ib_lru_dump file after restart. Percona XtraBackup discovers ib_lru_dump and backs it up automatically.
If the buffer restore option is enabled in my.cnf buffer pool will be in the warm state after backup is restored. To enable this set the variable innodb_buffer_pool_restore_at_startup =1 in Percona Server 5.5 or innodb_auto_lru_dump =1 in Percona Server 5.1.
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