This section describes
InnoDB recovery. Topics
To recover an
InnoDB database to the present
from the time at which the physical backup was made, you must
run MySQL server with binary logging enabled, even before taking
the backup. To achieve point-in-time recovery after restoring a
backup, you can apply changes from the binary log that occurred
after the backup was made. See
Section 7.5, “Point-in-Time (Incremental) Recovery Using the Binary Log”.
If your database becomes corrupted or disk failure occurs, you must perform the recovery using a backup. In the case of corruption, first find a backup that is not corrupted. After restoring the base backup, do a point-in-time recovery from the binary log files using mysqlbinlog and mysql to restore the changes that occurred after the backup was made.
In some cases of database corruption, it is enough to dump,
drop, and re-create one or a few corrupt tables. You can use the
CHECK TABLE statement to check
whether a table is corrupt, although
TABLE naturally cannot detect every possible kind of
corruption. You can use the Tablespace Monitor to check the
integrity of the file space management inside the tablespace
In some cases, apparent database page corruption is actually due
to the operating system corrupting its own file cache, and the
data on disk may be okay. It is best to try restarting the
computer first. Doing so may eliminate errors that appeared to
be database page corruption. If MySQL still has trouble starting
InnoDB consistency problems, see
Section 14.23.2, “Forcing InnoDB Recovery” for steps to start the
instance in recovery mode, which permits you to dump the data.
To recover from a MySQL server crash, the only requirement is to
restart the MySQL server.
automatically checks the logs and performs a roll-forward of the
database to the present.
rolls back uncommitted transactions that were present at the
time of the crash. During recovery, mysqld
displays output similar to this:
InnoDB: Log scan progressed past the checkpoint lsn 452854464 InnoDB: Database was not shut down normally! InnoDB: Starting crash recovery. InnoDB: Reading tablespace information from the .ibd files... InnoDB: Restoring possible half-written data pages from the doublewrite InnoDB: buffer... InnoDB: Doing recovery: scanned up to log sequence number 457028695 InnoDB: 1 transaction(s) which must be rolled back or cleaned up InnoDB: in total 990682 row operations to undo InnoDB: Trx id counter is 500 InnoDB: Starting an apply batch of log records to the database... InnoDB: Progress in percents: 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 InnoDB: Apply batch completed InnoDB: Waiting for the background threads to start InnoDB: Starting in background the rollback of uncommitted transactions InnoDB: Rolling back trx with id 3B1, 990682 rows to undo ... InnoDB: 5.5.55 started; log sequence number 457028695 ... ./mysqld: ready for connections.
process consists of several steps:
Redo log application
Redo log application is the first step and is performed during initialization, before accepting any connections. If all changes are flushed from the buffer pool to the tablespaces (
*.ibdfiles) at the time of the shutdown or crash, redo log application is skipped.
InnoDBalso skips redo log application if redo log files are missing at startup.
Removing redo logs to speed up recovery is not recommended, even if some data loss is acceptable. Removing redo logs should only be considered after a clean shutdown, with
Incomplete transactions are any transactions that were active at the time of crash or fast shutdown. The time it takes to roll back an incomplete transaction can be three or four times the amount of time a transaction is active before it is interrupted, depending on server load.
You cannot cancel transactions that are being rolled back. In extreme cases, when rolling back transactions is expected to take an exceptionally long time, it may be faster to start
3or greater. See Section 14.23.2, “Forcing InnoDB Recovery”.
Change buffer merge
Applying changes from the change buffer (part of the system tablespace) to leaf pages of secondary indexes, as the index pages are read to the buffer pool.
Deleting delete-marked records that are no longer visible to active transactions.
The steps that follow redo log application do not depend on the redo log (other than for logging the writes) and are performed in parallel with normal processing. Of these, only rollback of incomplete transactions is special to crash recovery. The insert buffer merge and the purge are performed during normal processing.
After redo log application,
to accept connections as early as possible, to reduce downtime.
As part of crash recovery,
InnoDB rolls back
transactions that were not committed or in
PREPARE state when the server crashed. The rollback is
performed by a background thread, executed in parallel with
transactions from new connections. Until the rollback operation
is completed, new connections may encounter locking conflicts
with recovered transactions.
In most situations, even if the MySQL server was killed
unexpectedly in the middle of heavy activity, the recovery
process happens automatically and no action is required of the
DBA. If a hardware failure or severe system error corrupted
InnoDB data, MySQL might refuse to start. In
this case, see Section 14.23.2, “Forcing InnoDB Recovery”.
For information about the binary log and
InnoDB crash recovery, see
Section 5.4.4, “The Binary Log”.