MDEV-25975 innodb_disallow_writes causes shutdown to hang

We will remove the parameter innodb_disallow_writes because it is badly
designed and implemented. The parameter was never allowed at startup.
It was only internally used by Galera snapshot transfer.
If a user executed
SET GLOBAL innodb_disallow_writes=ON;
the server could hang even on subsequent read operations.

During Galera snapshot transfer, we will block writes
to implement an rsync friendly snapshot, as follows:

sst_flush_tables() will acquire a global lock by executing
FLUSH TABLES WITH READ LOCK, which will block any writes
at the high level.

sst_disable_innodb_writes(), invoked via ha_disable_internal_writes(true),
will suspend or disable InnoDB background tasks or threads that could
initiate writes. As part of this, log_make_checkpoint() will be invoked
to ensure that anything in the InnoDB buf_pool.flush_list will be written
to the data files. This has the nice side effect that the Galera joiner
will avoid crash recovery.

The changes to sql/wsrep.cc and to the tests are based on a prototype
that was developed by Jan Lindström.

Reviewed by: Jan Lindström

1 files changed, 0 insertions, 28 deletions

diff --git a/mysql-test/suite/galera/r/galera_var_innodb_disallow_writes.result b/mysql-test/suite/galera/r/galera_var_innodb_disallow_writes.result
deleted file mode 100644
index 8750651612d..00000000000
--- a/mysql-test/suite/galera/r/galera_var_innodb_disallow_writes.result
+++ /dev/null
@@ -1,28 +0,0 @@
-connection node_1a;
-SET SESSION wsrep_sync_wait = 0;
-connection node_1;
-CREATE TABLE t1 (f1 INTEGER, f2 varchar(1024)) Engine=InnoDB;
-CREATE TABLE ten (f1 INTEGER) ENGINE=InnoDB;
-INSERT INTO ten VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);
-SET GLOBAL innodb_disallow_writes=ON;
-INSERT INTO t1 (f2) SELECT 'abcde ' FROM ten AS a1, ten AS a2, ten AS a3, ten AS a4;;
-connection node_2;
-INSERT INTO t1 (f2) SELECT 'fghij ' FROM ten AS a1, ten AS a2, ten AS a3, ten AS a4;
-SELECT COUNT(*) AS EXPECT_10000 FROM t1;
-EXPECT_10000
-10000
-connection node_1a;
-SET GLOBAL innodb_disallow_writes=OFF;
-connection node_1;
-SELECT COUNT(*) AS EXPECT_20000 FROM t1;
-EXPECT_20000
-20000
-connection node_2;
-SELECT COUNT(*) AS EXPECT_20000 FROM t1;
-EXPECT_20000
-20000
-connection node_1;
-connection node_2;
-DROP TABLE t1;
-DROP TABLE ten;
-disconnect node_1a;