Ever since commit 685d958e38
(MDEV-14425) mariadb-backup --backup had some trouble to keep up
with write workloads of the mariadbd server.
Debarun Banerjee found out that mariadb-backup --backup was
copying the log in the wrong way and not pausing when it made
sense to do so. This change includes his fix as well as some
dead code removal from xtrabackup_copy_mmap_logfile().
Some earlier changes to the default behaviour of mariadb-backup --backup
will be reverted, by making the configuration parameters OFF by default.
These parameters were basically working around this bug:
* commit 652f33e0a4 (MDEV-30000)
introduced --innodb-log-checkpoint-now and made it ON by default.
Making the server execute a log checkpoint can be really I/O intensive.
* commit 6acada713a (MDEV-34062)
introduced --innodb-log-file-mmap and made it ON by default on
Linux and FreeBSD. There are no documented semantics what should
happen to a memory mapping when there are concurrent pwrite(2)
operations by other processes. While it appears to work, it is safer
to default to clearly documented semantics.
xtrabackup_copy_logfile(): Add a parameter early_exit.
Always read a log snippet to the start of recv_sys.buf and assign
recv_sys.len to the read length. We used to shift recv_sys.buf
with memmove(). However, on recv_sys_t::PREMATURE_EOF we cannot know
which part of the mini-transaction was correctly read, because that
part of the ib_logfile0 may be concurrently modified by the server.
So, we will reread everything from the start of the mini-transaction.
xtrabackup_backup_func(): Invoke xtrabackup_copy_logfile(true),
allowing it to stop on every recv_sys_t::PREMATURE_EOF.
This will also avoid repeated "Retry" messages when there is no
more redo log to copy.
get_current_lsn(): Execute FLUSH ENGINE LOGS to ensure that
InnoDB will complete any buffered writes to the ib_logfile0
and ensure that everything up to the current LSN has been
written.
backup_wait_for_commit_lsn(): Wait for as much as is really needed.
This avoids an extra 5-second wait at the end of the backup.
xtrabackup_copy_mmap_logfile(): Remove some dead code, and add
debug assertions to demonstrate that the parser can only return
recv_sys_t::OK or recv_sys_t::GOT_EOF.
Problem:
========
- Mariabackup ignores tables-file option because it fails to
register the new entry in database hash cells. This issue was
caused by the commit 3c312d247c (MDEV-35190).
xb_register_filter_entry() fails to stop when it encounters the
empty list.
Solution:
=========
xb_register_filter_entry(): If there is no next member to
deference then it return pointer to existing element.
Added support to BACKUP STAGE to maria-backup
This is a port of the code from ES 10.6
See MDEV-5336 for backup stages description.
The following old options are not supported by the new code:
--rsync ; This is because rsync will not work on tables
that are in used.
--no-backup-locks ; This is disabled as mariadb-backup will always
use backup locks for better performance.
mariadb-backup with --prepare option could result in empty redo log
file. When --prepare is followed by --prepare --export, we exit early
in srv_start function without opening the ibdata1 tablespace. Later
while trying to read rollback segment header page, we hit the debug
assert which claims that the system space should already have been
opened.
There are two assert cases here.
Issue-1: System tablespace object is not there in fil space hash i.e.
srv_sys_space.open_or_create() is not called.
Issue-2: The system tablespace data file ibdata1 is not opened i.e.
fil_system.sys_space->open() is not called.
Fix: For empty redo log and restore operation, open system tablespace
before returning.
During data file creation, InnoDB holds dict_sys mutex, tries to
write page 0 of the file and flushes the file. This not only causing
unnecessary contention but also a deviation from the write-ahead
logging protocol.
The clean sequence of operations is that we first start a dictionary
transaction and write SYS_TABLES and SYS_INDEXES records that identify
the tablespace. Then, we durably write a FILE_CREATE record to the
write-ahead log and create the file.
Recovery should not unnecessarily insist that the first page of each
data file that is referred to by the redo log is valid. It must be
enough that page 0 of the tablespace can be initialized based on the
redo log contents.
We introduce a new data structure deferred_spaces that keeps track
of corrupted-looking files during recovery. The data structure holds
the last LSN of a FILE_ record referring to the data file, the
tablespace identifier, and the last known file name.
There are two scenarios can happen during recovery:
i) Sufficient memory: InnoDB can reconstruct the
tablespace after parsing all redo log records.
ii) Insufficient memory(multiple apply phase): InnoDB should
store the deferred tablespace redo logs even though
tablespace is not present. InnoDB should start constructing
the tablespace when it first encounters deferred tablespace
id.
Mariabackup copies the zero filled ibd file in backup_fix_ddl() as
the extension of .new file. Mariabackup test case does page flushing
when it deals with DDL operation during backup operation.
fil_ibd_create(): Remove the write of page0 and flushing of file
fil_ibd_load(): Return FIL_LOAD_DEFER if the tablespace has
zero filled page0
Datafile: Clean up the error handling, and do not report errors
if we are in the middle of recovery. The caller will check
Datafile::m_defer.
fil_node_t::deferred: Indicates whether the tablespace loading was
deferred during recovery
FIL_LOAD_DEFER: Returned by fil_ibd_load() to indicate that tablespace
file was cannot be loaded.
recv_sys_t::recover_deferred(): Invoke deferred_spaces.create() to
initialize fil_space_t based on buffered metadata and records to
initialize page 0. Ignore the flags in fil_name_t, because they are
intentionally invalid.
fil_name_process(): Update deferred_spaces.
recv_sys_t::parse(): Store the redo log if the tablespace id
is present in deferred spaces
recv_sys_t::recover_low(): Should recover the first page of
the tablespace even though the tablespace instance is not
present
recv_sys_t::apply(): Initialize the deferred tablespace
before applying the deferred tablespace records
recv_validate_tablespace(): Skip the validation for deferred_spaces.
recv_rename_files(): Moved and revised from recv_sys_t::apply().
For deferred-recovery tablespaces, do not attempt to rename the
file if a deferred-recovery tablespace is associated with the name.
recv_recovery_from_checkpoint_start(): Invoke recv_rename_files()
and initialize all deferred tablespaces before applying redo log.
fil_node_t::read_page0(): Skip page0 validation if the tablespace
is deferred
buf_page_create_deferred(): A variant of buf_page_create() when
the fil_space_t is not available yet
This is joint work with Thirunarayanan Balathandayuthapani,
who implemented an initial prototype.
When "--export" mariabackup option is used, mariabackup starts the server in
bootstrap mode to generate *.cfg files for the certain innodb tables.
The started instance of the server reads options from the file, pointed
out in "--defaults-file" mariabackup option.
If the server uses the same config file as mariabackup, and binlog is
switched on in that config file, then "mariabackup --prepare --export"
will create binary log files in the server's binary log directory, what
can cause issues.
The fix is to add "--skip-log-bin" in mysld options when the server is
started to generate *.cfg files.
full server recovery is performed .
We start "mysqld" with --bootstrap
and pass bootstrap script consisting of several FLUSH TABLES FOR export/
UNLOCK TABLES
InnoDB I/O and buffer pool interfaces and the redo log format
have been changed between MariaDB 10.1 and 10.2, and the backup
code has to be adjusted accordingly.
The code has been simplified, and many memory leaks have been fixed.
Instead of the file name xtrabackup_logfile, the file name ib_logfile0
is being used for the copy of the redo log. Unnecessary InnoDB startup and
shutdown and some unnecessary threads have been removed.
Some help was provided by Vladislav Vaintroub.
Parameters have been cleaned up and aligned with those of MariaDB 10.2.
The --dbug option has been added, so that in debug builds,
--dbug=d,ib_log can be specified to enable diagnostic messages
for processing redo log entries.
By default, innodb_doublewrite=OFF, so that --prepare works faster.
If more crash-safety for --prepare is needed, double buffering
can be enabled.
The parameter innodb_log_checksums=OFF can be used to ignore redo log
checksums in --backup.
Some messages have been cleaned up.
Unless --export is specified, Mariabackup will not deal with undo log.
The InnoDB mini-transaction redo log is not only about user-level
transactions; it is actually about mini-transactions. To avoid confusion,
call it the redo log, not transaction log.
We disable any undo log processing in --prepare.
Because MariaDB 10.2 supports indexed virtual columns, the
undo log processing would need to be able to evaluate virtual column
expressions. To reduce the amount of code dependencies, we will not
process any undo log in prepare.
This means that the --export option must be disabled for now.
This also means that the following options are redundant
and have been removed:
xtrabackup --apply-log-only
innobackupex --redo-only
In addition to disabling any undo log processing, we will disable any
further changes to data pages during --prepare, including the change
buffer merge. This means that restoring incremental backups should
reliably work even when change buffering is being used on the server.
Because of this, preparing a backup will not generate any further
redo log, and the redo log file can be safely deleted. (If the
--export option is enabled in the future, it must generate redo log
when processing undo logs and buffered changes.)
In --prepare, we cannot easily know if a partial backup was used,
especially when restoring a series of incremental backups. So, we
simply warn about any missing files, and ignore the redo log for them.
FIXME: Enable the --export option.
FIXME: Improve the handling of the MLOG_INDEX_LOAD record, and write
a test that initiates a backup while an ALGORITHM=INPLACE operation
is creating indexes or rebuilding a table. An error should be detected
when preparing the backup.
FIXME: In --incremental --prepare, xtrabackup_apply_delta() should
ensure that if FSP_SIZE is modified, the file size will be adjusted
accordingly.
