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Traditional theory and practice of write-ahead logging and of
database recovery focus on three failure classes: transaction
failures (typically due to deadlocks) resolved by transaction
rollback; system failures (typically power or software faults)
resolved by restart with log analysis, "redo," and "undo" phases;
and media failures (typically hardware faults) resolved by restore
operations that combine multiple types of backups and log replay.
The recent addition of single-page failures and single-page
recovery has opened new opportunities far beyond the original aim
of immediate, lossless repair of single-page wear-out in novel or
traditional storage hardware. In the contexts of system and media
failures, efficient single-page recovery enables on-demand
incremental "redo" and "undo" as part of system restart or media
restore operations. This can give the illusion of practically
instantaneous restart and restore: instant restart permits
processing new queries and updates seconds after system reboot and
instant restore permits resuming queries and updates on empty
replacement media as if those were already fully recovered. In the
context of node and network failures, instant restart and instant
restore combine to enable practically instant failover from a
failing database node to one holding merely an out-of-date backup
and a log archive, yet without loss of data, updates, or
transactional integrity. In addition to these instant recovery
techniques, the discussion introduces self-repairing indexes and
much faster offline restore operations, which impose no slowdown in
backup operations and hardly any slowdown in log archiving
operations. The new restore techniques also render differential and
incremental backups obsolete, complete backup commands on a
database server practically instantly, and even permit taking full
up-to-date backups without imposing any load on the database
server. Compared to the first version of this book, this second
edition adds sections on applications of single-page repair,
instant restart, single-pass restore, and instant restore.
Moreover, it adds sections on instant failover among nodes in a
cluster, applications of instant failover, recovery for file
systems and data files, and the performance of instant restart and
instant restore.
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