MDEV-38041: MariaBackup fails during rollback of inplace FTS alter table

[Thirunarayanan]

• The Jira issue number for this PR is: MDEV-38041

Description

Problem:

When an inplace ALTER operation is rolled back, InnoDB drops intermediate tables and their associated FTS internal tables. However, MariaBackup's DDL tracking can incorrectly report this as a backup failure.

The issue occurs because backup_set_alter_copy_lock() downgrades the MDL_BACKUP_DDL lock before the inplace phase of ALTER, allowing FTS internal tables to be dropped during the later phases of backup when DDL tracking is still active.

Solution:

backup_file_op_fail(): Ignore delete operations on FTS internal tables when not using --no-lock option, preventing false positive backup failures.

Release Notes

How can this PR be tested?

Run lot of rollback alter operation of fts table when mariabackup is running.
I have done some debug sync test case.

diff --git a/extra/mariabackup/backup_copy.cc b/extra/mariabackup/backup_copy.cc
index d4a90760f65..1b6a8ae48ec 100644
--- a/extra/mariabackup/backup_copy.cc
+++ b/extra/mariabackup/backup_copy.cc
@@ -1462,6 +1462,7 @@ bool backup_start(ds_ctxt *ds_data, ds_ctxt *ds_meta,
 
        corrupted_pages.backup_fix_ddl(ds_data, ds_meta);
 
+       DBUG_EXECUTE_IF("no_ddl_redo", my_sleep(100000 * 1000UL););
        // There is no need to stop slave thread before coping non-Innodb data when
        // --no-lock option is used because --no-lock option requires that no DDL or
        // DML to non-transaction tables can occur.
diff --git a/storage/innobase/handler/handler0alter.cc b/storage/innobase/handler/handler0alter.cc
index 43ea8c1466d..d70e28b8e15 100644
--- a/storage/innobase/handler/handler0alter.cc
+++ b/storage/innobase/handler/handler0alter.cc
@@ -9301,6 +9301,7 @@ inline bool rollback_inplace_alter_table(Alter_inplace_info *ha_alter_info,
     }
 
     DEBUG_SYNC(ctx->trx->mysql_thd, "before_commit_rollback_inplace");
+    DBUG_EXECUTE_IF("rollback_before_redo", my_sleep(20000000););
     commit_unlock_and_unlink(ctx->trx);
     if (fts_exist)
       purge_sys.resume_FTS();

Test case:

--source include/have_innodb.inc
CREATE TABLE t1 ( col1 INT, col_text TEXT, fulltext(col_text))ENGINE=InnoDB;
INSERT INTO t1 VALUES(1, "MARIADB"), (1, "mysql");
 
set DEBUG_DBUG="+d,rollback_before_redo";
send ALTER TABLE t1 ADD PRIMARY KEY(col1);
 
let $targetdir=$MYSQLTEST_VARDIR/tmp/backup;
let $backup_log=$MYSQLTEST_VARDIR/tmp/backup.log;
--exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf --backup --target-dir=$targetdir --log-copy-interval=1 --dbug=+d,no_ddl_redo >     $backup_log 2>&1 &
 
--error ER_DUP_ENTRY
--reap
DROP TABLE t1;

Basing the PR against the correct MariaDB version

• This is a new feature or a refactoring, and the PR is based against the main branch.
• This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.

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