There is a tiny chance for race condition during MDL acquisition.
If table is renamed just prior to
SELECT 1 FROM <table_name> LIMIT 0
then this query would fail, yet mariabackup --backup does not handle
it as fatal error and continues, only to fail later during file copy.
The fix is to die on error, of MDL lock query fails.
Itcan happen that the connection is already gone during the window
between quering I_S.PROCESSLIST and KILL QUERY.
Fix is to tolerate ER_NO_SUCH_THREAD returned from KILL QUERY.
Add small improvement in message "Killing MDL query " to actually output
the query.
Also do not try to kill queries that are already in Killed state.
System tablespace can be specified with absolute path, if innodb_data_home_dir
is empty.
This was not handled well by mariabackup
1. In backup phase, empty innodb_data_home_dir variable from server was
not recognized. full paths were stored in backup-my.ini, even if
it stored all files locally. thus prepare phase would not find the system
tablespace files.
2. In copy-back phase, copy would not be done to the absolute destination
path, as path would be stripped with trim_dotslash
This patch fixes the above defects.
concurrently.
There is a deadlock between
C1 mariabackup's connection that holds MDL locks
C2 Online ALTER TABLE that wants to have MDL exclusively
and tries to upgrade its mdl lock.
C3 another mariabackup's connection that does FLUSH TABLES (or FTWRL)
C3 waits waits for C2, which waits for C1, which waits for C3,
thus the deadlock.
MDL locks cannot be released until FLUSH succeeds, because
otherwise it would allow ALTER to sneak in, causing backup to abort and
breaking lock-ddl-per-table's promise.
The fix here workarounds the deadlock, by killing connections in
"Waiting for metadata lock" status (i.e ALTER). This killing continues
until FTWRL succeeds.
Killing connections is skipped in case --no-locks parameter
was passed to backup, because there won't be a FLUSH.
For the reference,in Percona's xtrabackup --lock-ddl-per-connection
silently implies --no-lock ie FLUSH is always skipped there.
A rather large part of fix is introducing DBUG capability to start
a query the new connection at the right moment of backup
compensating somewhat for mariabackup' lack of send_query or DBUG_SYNC.
Implement lock-ddl-per-table option that locks tables before it
is copied to backup, and helds the lock until backup finished
The "DDL-lock" itself is implemented as "SELECT * from <table> LIMIT 0",
inside a transaction, and "COMMIT" of this transaction is the DDL-unlock.
The test mariabackup.incremental_backup revealed a memory leak
in have_queries_to_wait_for(). The problem is that
xb_mysql_query() is being invoked with bool use_result=true
but the result is not being freed by mysql_store_result().
There are similar leaks in other functions.
have_queries_to_wait_for(): Invoke mysql_free_result() to
clean up after the mysql_store_result() that was invoked
by xb_mysql_query().
select_incremental_lsn_from_history(): Plug the leak on failure.
kill_long_queries(): Plug the memory leak.
(This function always leaked memory when it was called.)
Fixed null pointer dereference in parsing "show full processlist" output
with atoi().
Some Innodb background thread has NULL in 'Time' column,
thus backup would crash with when atoi is applied to null pointer.
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.
using "show variables", rather than take the value from my.cnf.
"show variables" is more accurate than my.cnf,it also works for parameters
set on the mysqld command line, which is especially important for MTR.
