MDEV-17433 Allow InnoDB start up with empty ib_logfile0 from mariabackup --prepare

A prepared backup from Mariabackup does not really need to contain any
redo log file, because all log will have been applied to the data files.

When the user copies a prepared backup to a data directory (overwriting
existing files), it could happen that the data directory already contained
redo log files from the past. mariabackup --copy-back) would delete the
old redo log files, but a user’s own copying script might not do that.
To prevent corruption caused by mixing an old redo log file with data
files from a backup, starting with MDEV-13311, Mariabackup would create
a zero-length ib_logfile0 that would prevent startup.

Actually, there is no need to prevent InnoDB from starting up when a
single zero-length file ib_logfile0 is present. Only if there exist
multiple data files of different lengths, then we should refuse to
start up due to inconsistency. A single zero-length ib_logfile0 should
be treated as if the log files were missing: create new log files
according to the configuration.

open_log_file(): Remove. There is no need to open the log files
at this point, because os_file_get_status() already determined
the size of the file.

innobase_start_or_create_for_mysql(): Move the creation of new
log files a little later, not when finding out that the first log
file does not exist, but after finding out that it does not exist
or it exists as a zero-length file.

2 files changed, 2 insertions, 2 deletions

diff --git a/mysql-test/suite/innodb/r/log_file_size.result b/mysql-test/suite/innodb/r/log_file_size.result
index e049b34ad81..89d5c6ac4d6 100644
--- a/mysql-test/suite/innodb/r/log_file_size.result
+++ b/mysql-test/suite/innodb/r/log_file_size.result
@@ -3,7 +3,7 @@ SELECT * FROM INFORMATION_SCHEMA.ENGINES
 WHERE engine = 'innodb'
 AND support IN ('YES', 'DEFAULT', 'ENABLED');
 ENGINE	SUPPORT	COMMENT	TRANSACTIONS	XA	SAVEPOINTS
-FOUND 1 /InnoDB: Log file .*ib_logfile0 size 0 is too small/ in mysqld.1.err
+FOUND 1 /InnoDB: Log file .*ib_logfile1 is of different size .* bytes than other log files 0 bytes!/ in mysqld.1.err
 CHECK TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	check	status	OK
diff --git a/mysql-test/suite/innodb/t/log_file_size.test b/mysql-test/suite/innodb/t/log_file_size.test
index 44cb155c7d9..1e6c7cd4d00 100644
--- a/mysql-test/suite/innodb/t/log_file_size.test
+++ b/mysql-test/suite/innodb/t/log_file_size.test
@@ -43,7 +43,7 @@ eval $check_no_innodb;
 --move_file $MYSQLD_DATADIR/ib_logfile.old $MYSQLD_DATADIR/ib_logfile.0
 --source include/shutdown_mysqld.inc
 let SEARCH_FILE= $MYSQLTEST_VARDIR/log/mysqld.1.err;
-let SEARCH_PATTERN= InnoDB: Log file .*ib_logfile0 size 0 is too small;
+let SEARCH_PATTERN= InnoDB: Log file .*ib_logfile1 is of different size .* bytes than other log files 0 bytes!;
 --source include/search_pattern_in_file.inc
 --source include/start_mysqld.inc
 CHECK TABLE t1;