[MDEV-15527] page_compressed compressed page partially during import tablespace Created: 2018-03-09  Updated: 2021-07-23  Resolved: 2021-03-30

Status: Closed
Project: MariaDB Server
Component/s: Storage Engine - InnoDB, Storage Engine - XtraDB
Affects Version/s: 10.1.3, 10.2.0, 10.3.0
Fix Version/s: 10.2.38, 10.3.29, 10.4.19, 10.5.10, 10.6.0

Type: Bug Priority: Major
Reporter: Marko Mäkelä Assignee: Thirunarayanan Balathandayuthapani
Resolution: Fixed Votes: 2
Labels: page_compression

Issue Links:
Relates
relates to MDEV-15529 IMPORT TABLESPACE unnecessarily uses ... Closed
relates to MDEV-25734 mbstream breaks page compression on XFS Closed
relates to MDEV-11696 Page Compression Has No Effect on Tab... Closed
Sprint: 10.3.6-1

 Description   

The CREATE TABLE attribute page_compressed that was introduced in MariaDB 10.1.3 has no effect when innodb_doublewrite=0. This is because the actual compression only takes place within the doublewrite buffer code path.

The purpose of the doublewrite buffer is to guarantee crash-safety in the event that InnoDB is killed in the middle of a page write. Because it could become a performance bottleneck for write-heavy workloads, some users may choose to set innodb_doublewrite=0 and take the risk that crash recovery may fail. (The page should be referred to by the redo log, and a log checkpoint should not be made while a page write is still in progress, so the page corruption should be detected at InnoDB startup.)

 Comments   
Comment by Marko Mäkelä [ 2018-03-09 ]

To repeat this, run:

./mtr --mysqld=--skip-innodb-doublewrite encryption.innodb-discard-import

And observe the test failure:

CURRENT_TEST: encryption.innodb-discard-import
 
--- /mariadb/10.2/mysql-test/suite/encryption/r/innodb-discard-import.result	2017-05-10 14:14:26.228207275 +0300
 
+++ /mariadb/10.2/mysql-test/suite/encryption/r/innodb-discard-import.reject	2018-03-09 14:32:57.500763121 +0200
 
@@ -129,6 +129,6 @@
 
 # t3 yes on expecting NOT FOUND
 
 NOT FOUND /tmpres/ in t3.ibd
 
 # t4 yes on expecting NOT FOUND
 
-NOT FOUND /mysql/ in t4.ibd
 
+FOUND 484 /mysql/ in t4.ibd
 
 DROP PROCEDURE innodb_insert_proc;
 
 DROP TABLE t1,t2,t3,t4;
 
 
 
mysqltest: Result content mismatch

MDEV-15529 will disable this part of the test.

Comment by Thirunarayanan Balathandayuthapani [ 2018-03-26 ] 

--source include/have_innodb.inc
 
 
 
let $innodb_compression_algo = `SELECT @@innodb_compression_algorithm`;
 
SET GLOBAL innodb_compression_algorithm = 1;
 
--let $MYSQLD_DATADIR = `SELECT @@datadir`
 
 
 
create table t1(c1 bigint not null, b char(200))  engine=innodb page_compressed=1;
 
show create table t1;
 
 
 
delimiter //;
 
create procedure innodb_insert_proc (repeat_count int)
 
begin
 
  declare current_num int;
 
  set current_num = 0;
 
  while current_num < repeat_count do
 
    insert into t1 values(current_num, repeat('maria', 30));
 
   set current_num = current_num + 1;
 
  end while;
 
end//
 
delimiter ;//
 
commit;
 
 
 
set autocommit=0;
 
call innodb_insert_proc(2000);
 
commit;
 
set autocommit=1;
 
 
 
SELECT COUNT(*) from t1;
 
-- let SEARCH_PATTERN=maria
 
-- let SEARCH_FILE=$MYSQLD_DATADIR/test/t1.ibd
 
--source include/search_pattern_in_file.inc
 
 
 
FLUSH TABLES t1 FOR EXPORT;
 
 
 
let MYSQLD_DATADIR=`select @@datadir`;
 
perl;
 
do "$ENV{MTR_SUITE_DIR}/include/innodb-util.pl";
 
ib_backup_tablespaces("test", "t1");
 
EOF
 
UNLOCK TABLES;
 
SELECT SPACE FROM INFORMATION_SCHEMA.innodb_sys_tables where name = "test/t1";
 
drop table t1;
 
 
 
create table t1(c1 bigint not null, b char(200))  engine=innodb page_compressed=1;
 
ALTER TABLE t1 DISCARD TABLESPACE;
 
--list_files $MYSQLD_DATADIR/test
 
 
 
 
 
perl;
 
do "$ENV{MTR_SUITE_DIR}/include/innodb-util.pl";
 
ib_discard_tablespaces("test", "t1");
 
ib_restore_tablespaces("test", "t1");
 
EOF
 
--list_files $MYSQLD_DATADIR/test
 
 
 
SELECT SPACE FROM INFORMATION_SCHEMA.innodb_sys_tables where name ="test/t1";
 
ALTER TABLE t1 IMPORT TABLESPACE;
 
SELECT COUNT(*) from t1;
 
SHOW CREATE TABLE t1;
 
-- let SEARCH_PATTERN=maria
 
-- let SEARCH_FILE=$MYSQLD_DATADIR/test/t1.ibd
 
--source include/search_pattern_in_file.inc
 
drop procedure innodb_insert_proc;
 
drop table t1;

The above test case can able to repeat the scenario.

String value("maria") found only in root page of clustered index. (3rd page)

 err = btr_root_adjust_on_import(index);

The above function call is omitted then t1.ibd doesn't contain maria. Need to check.

Comment by Marko Mäkelä [ 2018-03-26 ]

Commit a6ea7b353b5143f5a61fd37c246c49072ba8c421 looks OK to push (with minor changes), but I do not think that it qualifies as a full fix. We should punch holes to the page_compressed files even if the doublewrite buffer is disabled.

Comment by Thirunarayanan Balathandayuthapani [ 2021-03-01 ]

Commit a6ea7b353b5143f5a61fd37c246c49072ba8c421 has been pushed as a workaround of MDEV-15527. 

commit e27535093d1670fde6034c92366e8128b683b903
 
Author: Thirunarayanan Balathandayuthapani <thiru@mariadb.com>
 
Date:   Mon Mar 26 15:48:27 2018 +0530
 
    - Follow-up fix to MDEV-15229

It only writes zero in remaining uncompressed size of the page with zero.

Comment by Marko Mäkelä [ 2021-03-16 ]

I posted some comments for the 10.2-based patch. I think that we will also need a 10.5-based version, because the I/O code is quite different there.

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