This document provides a hands-on tutorial for advanced Percona XtraDB Cluster users. It discusses setting up a 3 node PXC cluster environment in VirtualBox and bootstrapping the initial cluster. It then covers topics like avoiding state snapshot transfers when restarting MySQL, recovering from clean and unclean shutdowns, and reproducing and diagnosing different types of conflicts through examples.

1. Advanced Percona XtraDB Cluster
in a nutshell... la suite
Hands on tutorial for advanced users!
1

2. Kenny 'kenji' Gryp
kenny.gryp@percona.com
Frédéric 'lefred' Descamps
lefred@percona.com
2

3. Setting Up
Environment
Bootstrapping
Certification Errors
Replication Failures
Galera Cache
Flow Control
Replication
Throughput
WAN Replication
Consistent Reads
Backups
Load Balancers
Challenges
Table of Contents
3

4. Are you ready?
Setting Up The Environment
4

5. Setting Up The Environment
Fetch a USB Stick, Install VirtualBox & Copy the 3 images
5

6. Testing The Environment
Start all 3 VirtualBox images
ssh/putty to:
pxc1: ssh root@localhost -p 8821
pxc2: ssh root@localhost -p 8822
pxc3: ssh root@localhost -p 8823
root password is vagrant
HAProxy is running on pxc1
(http://localhost:8881/)
Verify ssh between nodes
Open 2 ssh sessions to every node
6

7. Attention - Hands On!
When you see in the right bottom,
there is an exercise that you should do!
7

8. Easy, no?
Bootstrap A Cluster
8

9. Bootstrapping PXC
You all should know this already...
# service mysql bootstrap-pxc
# /etc/init.d/mysql boostrap-pxc
# /etc/init.d/mysql start --wsrep-new-cluster
or with systemd environments like Centos 7:
# systemctl mysql@bootstrap start
Today we are using 32-bit Centos 6.
For Emily, just to be complete....
pxc1# service mysql bootstrap-pxc
pxc2# service mysql start
pxc3# service mysql start
9

10. Bootstrapping PXC
Bootstrapping a node gives it permission to form a new cluster
Bootstrapping should NOT happen automatically without a system
with split-brain protection that can coordinate it. Usually this is
done manually
The bootstrapped node is the source of truth for all nodes going
forward
10

11. Bootstrapping PXC
Recap On IST/SST
IST: Incremental State Transfer
Only transfer missing transactions
SST: State Snapshot Transfer
Snapshot the whole database and transfer, using:
Percona XtraBackup
rsync
mysqldump
One node of the cluster is DONOR
11

12. Bootstrapping PXC
With Stop/Start Of MySQL
When you need to start a new cluster from scratch, you decide which
node to start with and you bootstrap it
# /etc/init.d/mysql start --wsrep-new-cluster
That node becomes the cluster source of truth (SSTs for all new nodes)
12

13. Bootstrapping PXC
Without Restarting MySQL
When a cluster is already partitioned and you want to bring it up again.
1 or more nodes need to be in Non-Primary state.
Choose the node that is newest and can be enabled (to work with
application)
To bootstrap online:
mysql> set global wsrep_provider_options="pc.bootstrap=true";
be sure there is NO OTHER PRIMARY partition or there will be a
split brain!!
13

14. Bootstrapping PXC
Without Restarting MySQL
Use Case:
Only 1 of the 3 nodes is available and the other 2 nodes crashed,
causing node 1 to go Non-Primary.
In Multi Datacenter environments:
DC1 has 2 nodes, DC2 has 1 node,
If DC1 dies, the single node in DC2 will go Non-Primary. To
activate secondary DC, a bootstrap is necessary
14

15. Recover Cleanly Shutdown Cluster
Run the application (run_app.sh haproxy-all) on pxc1
One by one, stop mysql on all 3 nodes
How can you know which node to bootstrap?
15

16. Recover Cleanly Shutdown Cluster
Run the application (run_app.sh haproxy-all) on pxc1
One by one, stop mysql on all 3 nodes
How can you know which node to bootstrap?
Solution
# cat /var/lib/mysql/grastate.dat
# GALERA saved state
version: 2.1
uuid: 3759f5c0-56f6-11e5-ad87-afbd92f4dcd2
seqno: 1933471
cert_index:
Bootstrap node with highest seqno and start other nodes.
16

17. Recover Unclean Stopped Cluster
Run the application (run_app.sh haproxy-all) on pxc1
On all nodes at the same time run:
# killall -9 mysqld mysqld_safe
How can you know which node has the latest commit?
17

18. Recover Unclean Stopped Cluster
Run the application (run_app.sh haproxy-all) on pxc1
On all nodes at the same time run:
# killall -9 mysqld mysqld_safe
How can you know which node has the latest commit?
Solution
# mysqld_safe --wsrep-recover
Logging to '/var/lib/mysql/error.log'.
Starting mysqld daemon with databases from /var/lib/mysql
WSREP: Running position recovery with --log_error='/var/lib/mysql/wsrep_recovery.Ln
WSREP: Recovered position 44e54b4b-5c69-11e5-83a3-8fc879cb495e:1719976
mysqld from pid file /var/lib/mysql/pxc1.pid ended
18

19. Recover Unclean Stopped Cluster
What methods can we use to bring back the cluster?
19

20. Recover Unclean Stopped Cluster
What methods can we use to bring back the cluster?
Solutions
Bootstrap the most accurate server
Since PXC 5.6.19-25.6 we have pc.recovery (enabled by default)
that uses the information stored in gvwstate.dat. We can then
just start MySQL on all 3 nodes at the same time
# service mysql restart
20

21. Avoiding SST
When MySQL cannot start due to an error, such as a
configuration error, an SST is always performed.
21

22. Avoiding SST
When MySQL cannot start due to an error, such as a
configuration error, an SST is always performed.
Let's try, stop MySQL on pxc2, modify my.cnf and add foobar under
[mysqld] section.
Then start MySQL, does it fail? Check /var/lib/mysql/error.log.
# /etc/init.d/mysql stop
# cat >> /etc/my.cnf << EOF
[mysqld]
foobar
EOF
# /etc/init.d/mysql start
22

23. Avoiding SST
When MySQL cannot start due to an error, such as a
configuration error, an SST is always performed.
Fix the error (remove the foobar configuration) and restart MySQL.
Does it perform SST?
Check /var/lib/mysql/error.log. Why?
23

24. Avoiding SST
When MySQL cannot start due to an error, such as a
configuration error, an SST is always performed.
Fix the error (remove the foobar configuration) and restart MySQL.
Does it perform SST?
Check /var/lib/mysql/error.log. Why?
SST is done, as we can see in the error.log:
[Warning] WSREP: Failed to prepare for incremental state transfer:
Local state UUID (00000000-0000-0000-0000-000000000000)
does not match group state UUID
(93a81eed-57b2-11e5-8f5e-82e53aab8d35): 1 (Operation not permitted)
...
WSREP_SST: [INFO] Proceeding with SST (20150916 19:13:50.990)
24

25. Avoiding SST
When MySQL cannot start due to an error, such as a
configuration error, an SST is always performed.
So how can we avoid SST?
It's easy, you need to hack /var/lib/mysql/grastate.dat.
Create the error again:
Bring node back in cluster
Add foobar to the configuration again
Start MySQL
25

26. Avoiding SST
When MySQL cannot start due to an error, such as a
configuration error, an SST is always performed.
# cat /var/lib/mysql/grastate.dat
# GALERA saved state
version: 2.1
uuid: 93a81eed-57b2-11e5-8f5e-82e53aab8d35
seqno: 1300762
cert_index:
26

27. Avoiding SST
When MySQL cannot start due to an error, such as a
configuration error, an SST is always performed.
# cat /var/lib/mysql/grastate.dat
# GALERA saved state
version: 2.1
uuid: 93a81eed-57b2-11e5-8f5e-82e53aab8d35
seqno: 1300762
cert_index:
When it fails due to an error, grastate.dat is reset to:
# GALERA saved state
version: 2.1
uuid: 00000000-0000-0000-0000-000000000000
seqno: -1
cert_index:
27

28. Avoiding SST
When MySQL cannot start due to an error, such as a
configuration error, an SST is always performed.
You need then to set the right uuid and seqno in grastate.dat
Run mysqld_safe --wsrep-recover to find the values to set:
[root@pxc2 mysql]# mysqld_safe --wsrep-recover
...
2015-09-16 19:26:14 6133 [Note] WSREP:
Recovered position: 93a81eed-57b2-11e5-8f5e-82e53aab8d35:1300762
28

29. Avoiding SST
When MySQL cannot start due to an error, such as a
configuration error, an SST is always performed.
Create grastate.dat with info from wsrep-recover:
# GALERA saved state
version: 2.1
uuid: 93a81eed-57b2-11e5-8f5e-82e53aab8d35
seqno: 1300762
cert_index:
Start MySQL again and check /var/lib/mysql/error.log:
[root@pxc2 mysql]# /etc/init.d/mysql start
...
150916 19:27:53 mysqld_safe
Assigning 93a81eed-57b2-11e5-8f5e-82e53aab8d35:1300762
to wsrep_start_position
...
WSREP_SST: [INFO] xtrabackup_ist received from donor:
Running IST (20150916 19:34:05.545
29

30. When putting in production unprepared...
Certification Errors
30

31. Certification
What it does:
Determine if writeset can be applied.
Based on unapplied earlier transactions on master
Such conflicts must come from other nodes
Happens on every node, individually
Deterministic
Results are not reported to other nodes in the cluster, as every node
does certification and is a determinstic process.
Pass: enter apply queue (commit success on master)
Fail: drop transaction (or return deadlock on master)
Serialized by GTID
Cost based on # of keys or # of rows
31

32. Certification
32

33. Certification
33

34. Certification
34

35. Certification
35

36. Certification
36

37. Certification
37

38. Certification
38

39. Conflict Detection
Local Certification Failure (lcf)
Transaction fails certification
Post-replication
Deadlock/Transaction Rollback
Status Counter: wsrep_local_cert_failures
Brute Force Abort (bfa)
(Most Common)
Deadlock/Transaction rolled back by applier threads
Pre-commit
Transaction Rollback
Status Counter: wsrep_local_bf_aborts
39

40. Conflict Deadlock/Rollback
note: Transaction Rollback can be gotten on any statement, including
SELECT and COMMIT
Example:
pxc1 mysql> commit;
ERROR 1213 (40001): Deadlock found when trying to get lock;
try restarting transaction
40

41. Multi-writer Conflict Types
Brute Force Abort (bfa)
Transaction rolled back by applier threads
Pre-commit
Transaction Rollback can be gotten on any statement, including
SELECT and COMMIT
Status Counter: wsrep_local_bf_aborts
41

42. Brute Force Abort (bfa)
42

43. Brute Force Abort (bfa)
43

44. Brute Force Abort (bfa)
44

45. Brute Force Abort (bfa)
45

46. Brute Force Abort (bfa)
46

47. Brute Force Abort (bfa)
47

48. Brute Force Abort (bfa)
48

49. Multi-writer Conflict Types
Local Certification Failure (lcf)
Transaction fails certification
Post-replication
Deadlock on commit
Status Counter: wsrep_local_cert_failures
49

50. Local Certification Failure (lcf)
50

51. Local Certification Failure (lcf)
51

52. Local Certification Failure (lcf)
52

53. Local Certification Failure (lcf)
53

54. Local Certification Failure (lcf)
54

55. Local Certification Failure (lcf)
55

56. Local Certification Failure (lcf)
56

57. Local Certification Failure (lcf)
57

58. Local Certification Failure (lcf)
58

59. Local Certification Failure (lcf)
59

60. Local Certification Failure (lcf)
60

61. Local Certification Failure (lcf)
61

62. Conflict Detection
Exercises!
62

63. Reproducing Conflicts - 1
On pxc1, create test table:
pxc1 mysql> CREATE TABLE test.deadlocks (
i INT UNSIGNED NOT NULL PRIMARY KEY,
j varchar(32),
t datetime
);
pxc1 mysql> INSERT INTO test.deadlocks VALUES (1, NULL, NULL);
Run myq_status on pxc1:
# myq_status wsrep
mycluster / pxc1 (idx: 1) / Galera 3.11(ra0189ab)
Cluster Node Repl Queue Ops Bytes Conflct Gcache Window
cnf # Stat Laten Up Dn Up Dn Up Dn lcf bfa ist idx dst appl comm
12 3 Sync N/A 0 0 0 0 0.0 0.0 0 0 1.8m 0 0 0
12 3 Sync N/A 0 0 0 0 0.0 0.0 0 0 1.8m 0 0 0
12 3 Sync N/A 0 0 0 0 0.0 0.0 0 0 1.8m 0 0 0
63

64. Reproducing Conflicts - 1
On pxc1:
pxc1 mysql> BEGIN;
pxc1 mysql> UPDATE test.deadlocks SET j='pxc1', t=now() WHERE i=1;
Before commit, go to pxc3:
pxc3 mysql> BEGIN;
pxc3 mysql> UPDATE test.deadlocks SET j='pxc3', t=now() WHERE i=1;
pxc3 mysql> COMMIT;
Now commit the transaction on pxc1:
pxc1 mysql> COMMIT;
pxc1 mysql> SELECT * FROM test.deadlocks;
64

65. Reproducing Conflicts - 1
It fails:
pxc1 mysql> commit;
ERROR 1213 (40001): Deadlock found when trying to get lock;
try restarting transaction
65

66. Reproducing Conflicts - 1
Which commit succeeded?
Is this a lcf or a bfa?
How would you diagnose this error?
66

67. Reproducing Conflicts - 1
Which commit succeeded? PXC3, first one that got in cluster.
Is this a lcf or a bfa? BFA
How would you diagnose this error?
show global status like 'wsrep_local_bf%';
show global status like 'wsrep_local_cert%';
+---------------------------+-------+
| Variable_name | Value |
+---------------------------+-------+
| wsrep_local_bf_aborts | 1 |
| wsrep_local_cert_failures | 0 |
+---------------------------+-------+
# myq_status wsrep
mycluster / pxc1 (idx: 1) / Galera 3.11(ra0189ab)
Wsrep Cluster Node Repl Queue Ops Bytes Conflct Gcache Win
time P cnf # Stat Laten Up Dn Up Dn Up Dn lcf bfa ist idx dst
10:49:43 P 12 3 Sync 1.1ms 0 0 0 0 0.0 0.0 0 0 3 3
10:49:44 P 12 3 Sync 1.1ms 0 0 0 0 0.0 0.0 0 0 3 3
10:49:45 P 12 3 Sync 1.1ms 0 0 0 0 0.0 0.0 0 0 3 3
10:49:46 P 12 3 Sync 1.1ms 0 0 0 1 0.0 0.3K 0 1 4 3
67

68. Reproducing Conflicts - 1
Log Conflicts
pxc1 mysql> set global wsrep_log_conflicts=on;
*** Priority TRANSACTION:
TRANSACTION 7743569, ACTIVE 0 sec starting index read
MySQL thread id 2, OS thread handle 0x93e78b70, query id 1395484 System lock
*** Victim TRANSACTION:
TRANSACTION 7743568, ACTIVE 9 sec
MySQL thread id 89984, OS thread handle 0x82bb1b70, query id 1395461 localhost root
*** WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 80 page no 3 n bits 72 index PRIMARY of table test.deadlocks
trx id 7743568 lock_mode X locks rec but not gap
2015-09-19 12:36:17 4285 [Note] WSREP: cluster conflict due to high priority
abort for threads:
2015-09-19 12:36:17 4285 [Note] WSREP: Winning thread:
THD: 2, mode: applier, state: executing, conflict: no conflict,
seqno: 1824234
SQL: (null)
2015-09-19 12:36:17 4285 [Note] WSREP: Victim thread:
THD: 89984, mode: local, state: idle, conflict: no conflict,
seqno: -1
SQL: (null)
68

69. Reproducing Conflicts - 1
Log Conflicts - Debug
pxc1 mysql> set global wsrep_debug=on;
[Note] WSREP: BF kill (1, seqno: 1824243), victim: (90473) trx: 7743601
[Note] WSREP: Aborting query: void
[Note] WSREP: kill IDLE for 7743601
[Note] WSREP: enqueuing trx abort for (90473)
[Note] WSREP: signaling aborter
[Note] WSREP: WSREP rollback thread wakes for signal
[Note] WSREP: client rollback due to BF abort for (90473), query: (null)
[Note] WSREP: WSREP rollbacker aborted thd: (90473 2649955184)
[Note] WSREP: Deadlock error for: (null)
69

70. Reproducing Conflicts - 2
rollback; all transactions on all mysql clients
ensure SET GLOBAL wsrep_log_conflicts=on; on all nodes;
run myq_status wsrep on pxc1 and pxc2
run run_app.sh lcf on pxc1 to reproduce a LCF
check:
output of run_app.sh lcf
myq_status
/var/lib/mysql/error.log
70

71. Reproducing Conflicts - 2
[root@pxc2 ~]# myq_status wsrep
mycluster / pxc2 (idx: 0) / Galera 3.12(r9921e73)
Wsrep Cluster Node Repl Queue Ops Bytes Conflct Gcache Win
time P cnf # Stat Laten Up Dn Up Dn Up Dn lcf bfa ist idx dst
13:28:15 P 47 3 Sync 1.1ms 0 0 0 0 0.0 0.0 0 0 7433 101
13:28:16 P 47 3 Sync 1.1ms 0 409 0 4 0.0 1.1K 0 0 7436 5
13:28:17 P 47 3 Sync 1.1ms 0 947 0 0 0.0 0.0 0 0 7436 5
13:28:18 P 47 3 Sync 1.1ms 0 1470 0 0 0.0 0.0 0 0 7436 5
13:28:19 P 47 3 Sync 1.1ms 0 1892 0 0 0.0 0.0 0 0 7436 5
13:28:20 P 47 3 Sync 1.1ms 0 2555 0 0 0.0 0.0 0 0 7436 5
13:28:21 P 47 3 Sync 1.1ms 0 3274 0 0 0.0 0.0 0 0 7436 5
13:28:22 P 47 3 Sync 1.1ms 0 3945 0 0 0.0 0.0 0 0 7436 5
13:28:23 P 47 3 Sync 1.1ms 0 4663 0 0 0.0 0.0 0 0 7436 5
13:28:24 P 47 3 Sync 1.1ms 0 5400 0 0 0.0 0.0 0 0 7436 5
13:28:25 P 47 3 Sync 1.1ms 0 6096 0 0 0.0 0.0 0 0 7436 5
13:28:26 P 47 3 Sync 1.1ms 0 6839 0 0 0.0 0.0 0 0 7436 5
13:28:27 P 47 3 Sync 1.1ms 0 6872 0 0 0.0 0.0 0 0 7436 5
13:28:28 P 47 3 Sync 1.1ms 0 6872 0 0 0.0 0.0 0 0 7436 5
13:28:29 P 47 3 Sync 1.1ms 0 6872 0 0 0.0 0.0 0 0 7436 5
13:28:30 P 47 3 Sync 1.1ms 0 5778 1 1102 0.3K 0.3M 0 0 8537 5
13:28:31 P 47 3 Sync 1.1ms 0 978 0 4838 0.0 1.4M 0 0 13k 5
13:28:32 P 47 3 Sync 1.1ms 0 0 1 985 0.3K 0.3M 2 0 14k 5
13:28:33 P 47 3 Sync N/A 0 0 0 0 0.0 0.0 0 0 14k 5
13:28:34 P 47 3 Sync N/A 0 0 0 0 0.0 0.0 0 0 14k 5
13:28:35 P 47 3 Sync N/A 0 0 0 0 0.0 0.0 0 0 14k 5
71

72. Reproducing Conflicts - 2
*** Priority TRANSACTION:
TRANSACTION 7787747, ACTIVE 0 sec starting index read
mysql tables in use 1, locked 1
1 lock struct(s), heap size 312, 0 row lock(s)
MySQL thread id 1, OS thread handle 0x93e78b70, query id 301870 System lock
*** Victim TRANSACTION:
TRANSACTION 7787746, ACTIVE 0 sec
mysql tables in use 1, locked 1
2 lock struct(s), heap size 312, 1 row lock(s), undo log entries 1
MySQL thread id 2575, OS thread handle 0x82369b70, query id 286919 pxc1 192.168
update test.test set sec_col = 0 where id = 1
[Note] WSREP: Winning thread:
THD: 1, mode: applier, state: executing, conflict: no conflict,
seqno: 1846028, SQL: (null)
[Note] WSREP: Victim thread:
THD: 2575, mode: local, state: committing, conflict: no conflict,
seqno: -1, SQL: update test.test set sec_col = 0 where id = 1
[Note] WSREP: BF kill (1, seqno: 1846028), victim: (2575) trx: 7787746
[Note] WSREP: Aborting query: update test.test set sec_col = 0 where id = 1
[Note] WSREP: kill trx QUERY_COMMITTING for 7787746
[Note] WSREP: trx conflict for key (1,FLAT8)258634b1 d0506abd:
source: 5cb369ab-5eca-11e5-8151-7afe8943c31a version: 3 local: 1
state: MUST_ABORT flags: 1 conn_id: 2575 trx_id: 7787746
seqnos (l: 21977, g: 1846030, s: 1846027, d: 1838545, ts: 161299135504641)
<--X-->
source: 9b376860-5e09-11e5-ac17-e6e46a2459ee version: 3 local: 0
state: APPLYING flags: 1 conn_id: 95747 trx_id: 7787229
72

73. Reproducing Conflicts
Summary
Conflicts are of a concern when determining if PXC is a fit for the
application:
Long running transactions increase chance of conflicts
Heavy write workload on multiple nodes
Large transactions increase chance of conflicts
Mark Callaghan's law a given row can't be modified more often
than 1/RTT times a second
These issues can usually be resolved by writing to 1 node only.
73

74. Reproducing Conflicts - Summary
74

75. Reproducing Conflicts - Summary
75

76. Reproducing Conflicts - Summary
76

77. What the ...?
Replication Failures
77

78. Replication Failure
When Do They Happen?
When a Total Order Isolation (TOI) error happened
DDL error: CREATE TABLE, ALTER TABLE...
GRANT failed
When there was a node inconsistency
Bug in Galera replication
Human Error, for example skipping binary log
(SQL_LOG_BIN=0) when doing writes
78

79. Replication Failure
What Happens?
At every error:
A GRA_*.log file is created into the MySQL datadir
[root@pxc1 ~]# ls -alsh1 /var/lib/mysql/GRA_*
-rw-rw----. 1 mysql 89 Sep 15 10:26 /var/lib/mysql/GRA_1_127792.log
-rw-rw----. 1 mysql 83 Sep 10 12:00 /var/lib/mysql/GRA_2_5.log
A message is written to the errorlog
/var/lib/mysql/error.log
It's possible to decode them, they are binary logs
They can be safely removed
79

80. Replication Failure
Reading GRA Contents
Run Application only on pxc1 using only pxc1 as writer:
# run_app.sh pxc1
pxc1 mysql> create table test.nocolumns;
What do you get?
80

81. Replication Failure
Reading GRA Contents
Run Application only on pxc1 using only pxc1 as writer:
# run_app.sh pxc1
pxc1 mysql> create table test.nocolumns;
What do you get?
ERROR 1113 (42000): A table must have at least 1 column
81

82. Replication Failure
Reading GRA Contents
Run Application only on pxc1 using only pxc1 as writer:
# run_app.sh pxc1
pxc1 mysql> create table test.nocolumns;
What do you get?
ERROR 1113 (42000): A table must have at least 1 column
Error Log Other Nodes:
[ERROR] Slave SQL: Error 'A table must have at least 1 column' on query.
Default database: ''. Query: 'create table test.nocolumns', Error_code: 1113
[Warning] WSREP: RBR event 1 Query apply warning: 1, 1881065
[Warning] WSREP: Ignoring error for TO isolated action:
source: 9b376860-5e09-11e5-ac17-e6e46a2459ee version: 3 local: 0
state: APPLYING flags: 65 conn_id: 106500 trx_id: -1
seqnos (l: 57292, g: 1881065, s: 1881064, d: 1881064, ts: 76501555632582)
82

83. Replication Failure
Making GRA Header File
note: Binary log headers only differ between versions, they can be
reused
Get a binary log without checksums:
Create the GRA_header file with the new binary log:
dd if=/var/lib/mysql/pxc2-bin.000018 bs=120 count=1
of=/root/GRA_header
pxc2 mysql> set global binlog_checksum=0;
pxc2 mysql> flush binary logs;
pxc2 mysql> show master status;
+-----------------+----------+--------------+------------------+-------------------
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set
+-----------------+----------+--------------+------------------+-------------------
| pxc2-bin.000018 | 790333 | | |
+-----------------+----------+--------------+------------------+-------------------
83

84. Replication Failure
Reading GRA Contents
Join the header and one GRA*.log file (note the seqno of 1881065)
cat /root/GRA_header /var/lib/mysql/GRA_1_1881065.log
>> /root/GRA_1_1881065-bin.log
View the content with mysqlbinlog
mysqlbinlog -vvv /root/GRA_1_1881065-bin.log
84

85. Replication Failure
Node Consistency Compromised
Delete some data while skipping binary log completely:
pxc2 mysql> set sql_log_bin=0;
Query OK, 0 rows affected (0.00 sec)
pxc2 mysql> delete from sbtest.sbtest1 limit 100;
Query OK, 100 rows affected (0.00 sec)
Repeat the DELETE until pxc2 crashes...
85

86. Replication Failure
Node Consistency Compromised
Error:
[ERROR] Slave SQL: Could not execute Update_rows event
on table sbtest.sbtest1;
Can't find record in 'sbtest1', Error_code: 1032;
handler error HA_ERR_KEY_NOT_FOUND;
the event's master log FIRST, end_log_pos 540, Error_code: 1032
[Warning] WSREP: RBR event 3 Update_rows apply warning: 120, 1890959
[Warning] WSREP: Failed to apply app buffer: seqno: 1890959, status: 1
at galera/src/trx_handle.cpp:apply():351
Retrying 2th time ...
Retrying 4th time ...
[ERROR] WSREP: Failed to apply trx:
source: 9b376860-5e09-11e5-ac17-e6e46a2459ee version: 3 local: 0
state: APPLYING flags: 1 conn_id: 117611 trx_id: 7877213
seqnos (l: 67341, g: 1890959, s: 1890958, d: 1890841, ts: 78933399926835)
[ERROR] WSREP: Failed to apply trx 1890959 4 times
[ERROR] WSREP: Node consistency compromized, aborting...
...
[Note] WSREP: /usr/sbin/mysqld: Terminated.
86

87. Replication Failure
Node Consistency Compromised
[root@pxc2 ~]# cat /root/GRA_header /var/lib/mysql/GRA_1_1890959.log |
mysqlbinlog -vvv -
BINLOG '
...MDQwNjUyMjMwMTQ=...
'/*!*/;
### UPDATE sbtest.sbtest1
### WHERE
### @1=3528 /* INT meta=0 nullable=0 is_null=0 */
### @2=4395 /* INT meta=0 nullable=0 is_null=0 */
### @3='01945529982-83991536409-94055999891-11150850160-46682230772-19159811582-7
### @4='92814455222-06024456935-25380449439-64345775537-04065223014' /* STRING(60
### SET
### @1=3528 /* INT meta=0 nullable=0 is_null=0 */
### @2=4396 /* INT meta=0 nullable=0 is_null=0 */
### @3='01945529982-83991536409-94055999891-11150850160-46682230772-19159811582-7
### @4='92814455222-06024456935-25380449439-64345775537-04065223014' /* STRING(60
# at 660
#150919 15:56:36 server id 1 end_log_pos 595 Table_map: sbtest.sbtest1 mapped to
# at 715
#150919 15:56:36 server id 1 end_log_pos 1005 Update_rows: table id 70 flags: STM
...
87

88. Gcache... what's that ?
Galera Cache
88

89. Galera Cache
All nodes contain a Cache of recent writesets, used to perform IST
used to store the writesets in circular buffer style
89

90. Galera Cache
All nodes contain a Cache of recent writesets, used to perform IST
used to store the writesets in circular buffer style
preallocated file with a specific size, configurable:
wsrep_provider_options = "gcache.size=1G"
default size is 128M
90

91. Galera Cache
All nodes contain a Cache of recent writesets, used to perform IST
used to store the writesets in circular buffer style
preallocated file with a specific size, configurable:
wsrep_provider_options = "gcache.size=1G"
default size is 128M
Galera Cache is mmaped (I/O buffered to memory)
So OS might swap (set vm.swappiness to 10)
use fincore-linux or dbsake fincore to see how much of the
file is cached in memory
91

92. Galera Cache
All nodes contain a Cache of recent writesets, used to perform IST
used to store the writesets in circular buffer style
preallocated file with a specific size, configurable:
wsrep_provider_options = "gcache.size=1G"
default size is 128M
Galera Cache is mmaped (I/O buffered to memory)
So OS might swap (set vm.swappiness to 10)
use fincore-linux or dbsake fincore to see how much of the
file is cached in memory
status counter wsrep_local_cached_downto to find last seqno
in the gcache
wsrep_gcache_pool_size shows the size of the page pool
and/or dynamic memroy allocated for gcache (since PXC 5.6.24)
92

93. Galera Cache
Calculating Optimal Size
It would be great that we could handle 1 hour of changes in the galera
cache for IST.
How large does the Galera cache need to be?
93

94. Galera Cache
Calculating Optimal Size
It would be great that we could handle 1 hour of changes in the galera
cache for IST.
How large does the Galera cache need to be?
We can calculate how much writes happen over time
wsrep_replicated_bytes: writesets sent to other nodes
wsrep_received_bytes: writesets received from other nodes
94

95. Galera Cache
Calculating Optimal Size
It would be great that we could handle 1 hour of changes in the galera
cache for IST.
How large does the Galera cache need to be?
We can calculate how much writes happen over time
wsrep_replicated_bytes: writesets sent to other nodes
wsrep_received_bytes: writesets received from other nodes
SHOW GLOBAL STATUS LIKE 'wsrep_%d_bytes';
SELECT SLEEP(60);
SHOW GLOBAL STATUS LIKE 'wsrep_%d_bytes';
Sum up both replicated and received
for each status and subtract.
95

96. Galera Cache
Calculating Optimal Size
Easier to do is:
SELECT ROUND(SUM(bytes)/1024/1024*60) AS megabytes_per_hour FROM
(SELECT SUM(VARIABLE_VALUE) * -1 AS bytes
FROM information_schema.GLOBAL_STATUS
WHERE VARIABLE_NAME IN ('wsrep_received_bytes',
'wsrep_replicated_bytes')
UNION ALL
SELECT sleep(60) AS bytes
UNION ALL
SELECT SUM(VARIABLE_VALUE) AS bytes
FROM information_schema.GLOBAL_STATUS
WHERE VARIABLE_NAME IN ('wsrep_received_bytes',
'wsrep_replicated_bytes')
) AS COUNTED
+--------------------+
| megabytes_per_hour |
+--------------------+
| 302 |
+--------------------+
1 row in set (1 min 0.00 sec)
96

97. Galera Cache
How Much Filesystem Cache Used?
Check galera cache's memory usage using dbsake:
dbsake fincore /var/lib/mysql/galera.cache
/var/lib/mysql/galera.cache: total_pages=32769 cached=448 percent=1.37
97

98. Hey! Wait for me!
Flow Control
98

99. Flow Control
Avoiding nodes drift behind (slave lag?)
Any node in the cluster can ask the other nodes to pause writes if it
lags behind too much.
Caused by wsrep_local_recv_queue exceeding a node’s
gcs.fc_limit
Can cause all writes on all nodes in the entire cluster to be
stalled.
99

100. Flow Control
100

101. Flow Control
101

102. Flow Control
102

103. Flow Control
103

104. Flow Control
104

105. Flow Control
105

106. Flow Control
106

107. Flow Control
107

108. Flow Control
108

109. Flow Control
109

110. Flow Control
110

111. Flow Control
111

112. Flow Control
112

113. Flow Control
113

114. Flow Control
114

115. Flow Control
115

116. Flow Control
116

117. Flow Control
117

118. Flow Control
118

119. Flow Control
119

120. Flow Control
Status Counters
wsrep_flow_control_paused_ns:
nanoseconds since starts of node did the cluster get stalled.
wsrep_flow_control_recv:
Amount of flow control messages received from other nodes
wsrep_flow_control_sent:
Amount of flow control messages sent to other nodes
(wsrep_flow_control_paused: Only use in Galera 2
% of the time the cluster was stalled since last SHOW GLOBAL
STATUS)
120

121. Flow Control
Observing Flow Control
Run the application (run_app.sh)
Run myq_status wsrep on all nodes.
Take a read lock on pxc3 and observe its effect on the cluster.
FLUSH TABLES WITH READ LOCK
121

122. pxc1
run_app.sh
all nodes:
myq_status wsrep
Flow Control
Observing Flow Control
Run the application (run_app.sh)
Run myq_status wsrep on all nodes.
Take a read lock on pxc3 and observe its effect on the cluster.
FLUSH TABLES WITH READ LOCK
pxc3 mysql> flush tables with read lock;
wait until flow control kicks in...
pcx3 mysql> unlock tables;
122

123. Flow Control
Increase the limit
Increase the flow control limit on pxc3 to 20000 and perform the same
exercise as previously.
123

124. pxc1
run_app.sh
all nodes:
myq_status wsrep
Flow Control
Increase the limit
Increase the flow control limit on pxc3 to 20000 and perform the same
exercise as previously.
pxc3 mysql> set global wsrep_provider_options="gcs.fc_limit=20000";
pxc3 mysql> flush tables with read lock;
wait until flow control kicks in...
pcx3 mysql> unlock tables;
124

125. Flow Control
Increase the limit
What do you see?
A node can lag behind more before sending flow control messages.
This can be controlled per node.
Is there another alternative?
125

126. Flow Control
DESYNC mode
It's possible to let a node going behind the flow control limit.
This can be performed by setting wsrep_desync=ON
Try the same exercises but enable DESYNC on pxc3.
126

127. pxc1
run_app.sh
all nodes:
myq_status wsrep
Flow Control
DESYNC mode
It's possible to let a node going behind the flow control limit.
This can be performed by setting wsrep_desync=ON
Try the same exercises but enable DESYNC on pxc3.
pxc3 mysql> set global wsrep_provider_options="gcs.fc_limit=16";
pxc3 mysql> set global wsrep_desync=on;
Don't forget when done:
pcx3 mysql> unlock tables;
127

128. How much more can we handle?
Max Replication Throughput
128

129. Max Replication Throughput
We can measure the write throughput of a node/cluster:
Put a node in wsrep_desync=on to avoid flow control messages
being sent
Lock the replication with FLUSH TABLES WITH READ LOCK
Wait and build up a queue for a certain amount of time
Unlock replication again with UNLOCK TABLES
Measure how fast it syncs up again
Compare with normal workload
129

130. Max Replication Throughput
Measure
On pxc2 run
show global status like 'wsrep_last_committed';
select sleep(60);
show global status like 'wsrep_last_committed';
One Liner:
SELECT ROUND(SUM(trx)/60) AS transactions_per_second FROM
(SELECT VARIABLE_VALUE * -1 AS trx
FROM information_schema.GLOBAL_STATUS
WHERE VARIABLE_NAME = 'wsrep_last_committed'
UNION ALL SELECT sleep(60) AS trx
UNION ALL SELECT VARIABLE_VALUE AS trx
FROM information_schema.GLOBAL_STATUS
WHERE VARIABLE_NAME = 'wsrep_last_committed') AS COUNTED;
+-------------------------+
| transactions_per_second |
+-------------------------+
| 185 |
+-------------------------+
130

131. Max Replication Throughput
Measure
The following stored function is already installed:
USE test; DROP FUNCTION IF EXISTS galeraWaitUntilEmptyRecvQueue;
DELIMITER $$
CREATE
DEFINER=root@localhost FUNCTION galeraWaitUntilEmptyRecvQueue()
RETURNS INT UNSIGNED READS SQL DATA
BEGIN
DECLARE queue INT UNSIGNED;
DECLARE starttime TIMESTAMP;
DECLARE blackhole INT UNSIGNED;
SET starttime = SYSDATE();
SELECT VARIABLE_VALUE AS trx INTO queue
FROM information_schema.GLOBAL_STATUS
WHERE VARIABLE_NAME = 'wsrep_local_recv_queue';
WHILE queue > 1 DO /* we allow the queue to be 1 */
SELECT VARIABLE_VALUE AS trx INTO queue
FROM information_schema.GLOBAL_STATUS
WHERE VARIABLE_NAME = 'wsrep_local_recv_queue';
SELECT SLEEP(1) into blackhole;
END WHILE;
RETURN SYSDATE() - starttime;
END$$
131

132. Max Replication Throughput
Measure
SET GLOBAL wsrep_desync=on;
FLUSH TABLES WITH READ LOCK;
...wait until the queue rises to be quite high, about 20.000
UNLOCK TABLES; use test;
SELECT sum(trx) as transactions, sum(duration) as time,
IF(sum(duration) < 5, 'DID NOT TAKE LONG ENOUGH TO BE ACCURATE',
ROUND(SUM(trx)/SUM(duration)))
AS transactions_per_second
FROM
(SELECT VARIABLE_VALUE * -1 AS trx, null as duration
FROM information_schema.GLOBAL_STATUS
WHERE VARIABLE_NAME = 'wsrep_last_committed'
UNION ALL
SELECT null as trx, galeraWaitUntilEmptyRecvQueue() AS duration
UNION ALL
SELECT VARIABLE_VALUE AS trx, null as duration
FROM information_schema.GLOBAL_STATUS
WHERE VARIABLE_NAME = 'wsrep_last_committed'
) AS COUNTED;
+--------------+------+-------------------------+
| transactions | time | transactions_per_second |
+--------------+------+-------------------------+
| 17764 | 11 | 1615 |
132

133. Max Replication Throughput
Measure
Normal Workload: 185 tps
During Catchup: 1615 tps
Capacity: 185/1615= 11,5% of capacity
133

134. A wired world
Networking
134

135. Networking
With Synchronous Replication, It Matters
Network issues cause cluster issues, much faster compared to
asynchronous replication.
Network Partitioning
Nodes joining/leaving
Causing clusters to go Non-Primary,
not accepting any reads and writes anymore.
Latency has an impact on response time:
at COMMIT of a transaction
depending on wsrep_sync_wait setting for other statements
too.
135

136. Networking
Status Variables
pxc2 mysql> show global status like 'wsrep_evs_repl_latency';
+------------------------+-------------------------------------------------+
| Variable_name | Value |
+------------------------+-------------------------------------------------+
| wsrep_evs_repl_latency | 0.000745194/0.00175792/0.00832816/0.00184453/16 |
+------------------------+-------------------------------------------------+
Reset Interval with evs.stats_report_period=1min
# myq_status wsrep_latency`:
mycluster / pxc2 (idx: 2) / Galera 3.12(r9921e73)
Wsrep Cluster Node Ops Latencies
time P cnf # Stat Up Dn Size Min Avg Max Dev
22:55:48 P 53 3 Sync 0 65 9 681µs 1307µs 4192µs 1032µs
22:55:49 P 53 3 Sync 0 52 10 681µs 1274µs 4192µs 984µs
22:55:50 P 53 3 Sync 0 47 10 681µs 1274µs 4192µs 984µs
22:55:51 P 53 3 Sync 0 61 11 681µs 1234µs 4192µs 947µs
136

137. Networking
Latency
On pxc1, start the 'application':
# myq_status wsrep_latency
mycluster / pxc2 (idx: 2) / Galera 3.12(r9921e73)
Wsrep Cluster Node Ops Latencies
time P cnf # Stat Up Dn Size Min Avg Max Dev
23:02:44 P 53 3 Sync 0 48 7 777µs 1236µs 2126µs 434µs
23:02:45 P 53 3 Sync 0 47 7 777µs 1236µs 2126µs 434µs
23:02:46 P 53 3 Sync 0 58 7 777µs 1236µs 2126µs 434µs
run_app.sh pxc1
[1125s] tps: 51.05, reads: 687.72, writes: 204.21, response time: 10.54ms (95%), er
[1126s] tps: 33.98, reads: 475.77, writes: 135.94, response time: 15.07ms (95%), er
[1127s] tps: 42.01, reads: 588.19, writes: 168.05, response time: 12.79ms (95%), er
# myq_status wsrep
Wsrep Cluster Node Repl Queue Ops Bytes Conflct Gcache Wind
time P cnf # Stat Laten Up Dn Up Dn Up Dn lcf bfa ist idx dst
23:02:44 P 53 3 Sync 1.2ms 0 0 0 49 0.0 80K 0 0 77k 178
23:02:45 P 53 3 Sync 1.2ms 0 0 0 43 0.0 70K 0 0 77k 176
23:02:46 P 53 3 Sync 1.2ms 0 0 0 55 0.0 90K 0 0 77k 164
137

138. Networking
WAN Impact on Latency
Change from a LAN setup into a cluster across 2 datacenters
last_node_to_dc2.sh enable
138

139. Networking
WAN Impact on Latency
last_node_to_dc2.sh enable
What can we observe in the cluster after running this command?
139

140. Networking
WAN Impact on Latency
last_node_to_dc2.sh enable
What can we observe in the cluster after running this command?
myq_status wsrep_latency is up 200ms
run_app.sh throughput is a lot lower
run_app.sh response time is a lot higher
mycluster / pxc3 (idx: 0) / Galera 3.12(r9921e73)
Wsrep Cluster Node Ops Latencies
time P cnf # Stat Up Dn Size Min Avg Max Dev
23:23:34 P 53 3 Sync 0 14 6 201ms 202ms 206ms 2073µs
23:23:35 P 53 3 Sync 0 16 6 201ms 202ms 206ms 2073µs
23:23:36 P 53 3 Sync 0 14 6 201ms 202ms 206ms 2073µs
23:23:37 P 53 3 Sync 0 14 6 201ms 202ms 206ms 2073µs
23:23:38 P 53 3 Sync 0 14 6 201ms 202ms 206ms 2073µs
140

141. Networking
WAN Impact on Latency
Why Is that?
141

142. Networking
WAN Impact on Latency
Why Is that?
Don't forget this is synchronous replication, the writeset is replicated
synchronously.
Delivers the writeset to all nodes in the cluster at trx commit.
And all nodes acknowledging the writeset
Generates a GLOBAL ORDER for that transaction (GTID)
Cost is ~roundtrip latency for COMMIT to furthest node
GTID serialized, but many writesets can be replicating in parallel
Remember Mark Callaghan's Law a given row can't be modified
more often than 1/RTT times a second
142

143. Networking
WAN Configuration
Don't forget in WAN to use higher timeouts and send windows:
evs.user_send_window=2 ~> 256
evs.send_window=4 ~> 512
evs.keepalive_period=PT1S ~> PT1S
evs.suspect_timeout=PT5S ~> PT15S
evs.inactive_timeout=PT15S ~> PT45S
Don't forget to disable the WAN:
last_node_to_dc2.sh disable
143

144. Networking
WAN Configuration - Bandwidth
How to reduce bandwith used between datacenters?
144

145. Networking
WAN Configuration - Bandwidth
How to reduce bandwith used between datacenters?
Use segments (gmcast.segment) to reduce network traffic
between datacenters
Use minimal binlog_row_image to reduce binary log size
repl.key_format = FLAT8 which by default is already smallest
145

146. Networking
Replication Without Segments
Here we have a cluster spread across 2 datacenters
146

147. Networking
Replication Without Segments
A transaction executed on node1
147

148. Networking
Replication Without Segments
A transaction executed on node1
will be sent to all other nodes
148

149. Networking
Replication Without Segments
As writes are accepted everywhere, every node therefore communicate
with all nodes, including arbitrator nodes
149

150. Networking
Replication With Segments
Galera 3.0 introduced the segment concept
Replication traffic is minimized between segments
Donor selection is preferred on local segment
150

151. Networking
Replication With Segments
Transactions are only sent once to other segments
151

152. Networking
Replication With Segments
They do not always go through the same nodes, they all still need to be
able to connect to eachother.
152

153. Networking
Replication With Segments
Run the run_app.sh on pxc1
On another terminal on pxc1, run speedometer
speedometer -r eth1 -t eth1 -l -m 524288
Change the segment on pxc2 an pxc3 in /etc/my.cnf and restart
MySQL (this is not dynamic)
wsrep_provider_options='gmcast.segment=2'
Check the bandwidth usage again.
How do you explain this?
153

154. Networking
Replication With Segments
Bandwidth Transmit usage drops a lot (/2)
154

155. Networking
Binlog Row Image Format
On pxc1 run speedometer again::
speedometer -r eth1 -t eth1 -l -m 262144
On pxc1, set the binlog_row_image=minimal:
pxc1 mysql> SET GLOBAL binlog_row_image=minimal;
Check the bandwith usage
155

156. Networking
Binlog Row Image Format
On pxc1 run speedometer again::
speedometer -r eth1 -t eth1 -l -m 262144
On pxc1, set the binlog_row_image=minimal:
pxc1 mysql> SET GLOBAL binlog_row_image=minimal;
Check the bandwith usage
156

157. Networking
Not Completely Synchronous
Applying transactions is asynchronous
By default, reads on different nodes might show stale data.
Practically, flow control prevents this from lagging too much
behind, reducing stale data.
Read Consistency can be configured: We can enforce a read reads
the latest committed data, cluster wide.
What if we absolutely need consistency?
157

158. Networking
Not Completely Synchronous
What if we absolutely need consistency?
Since PXC 5.6.20-27.7:
SET <session|global> wsrep_sync_wait=[1|2|4];
1 Indicates check on READ statements, including SELECT,
SHOW, BEGIN/START TRANSACTION.
2 Indicates check on UPDATE and DELETE statements.
4 Indicates check on INSERT and REPLACE statements
Before: <session|global> wsrep_causal_reads=[1|0];
158

159. Networking
Consistent Reads & Latency
How does enabling WSREP_SYNC_WAIT consistent reads affect WAN
environments?
Stop the application run_app.sh
Move the last node to DC2:
last_node_to_dc2.sh enable
On pxc1, run:
pxc1 mysql> select * from sbtest.sbtest1 where id = 4;
...
1 row in set (0.00 sec)
159

160. Networking
Consistent Reads & Latency
Now change the causality check to ensure that READ statements are in
sync, and perform the same SELECT:
pxc1 mysql> SET SESSION wsrep_sync_wait=1;
pxc1 mysql> select * from sbtest.sbtest1 where id = 4;
What do you see ?
160

161. Networking
Consistent Reads & Latency
Now change the causality check to ensure that READ statements are in
sync, and perform the same SELECT:
pxc1 mysql> SET SESSION wsrep_sync_wait=1;
pxc1 mysql> select * from sbtest.sbtest1 where id = 4;
What do you see ?
...
1 row in set (0.20 sec)
161

162. Networking
Consistent Reads & Latency
Now change the causality check to ensure that READ statements are in
sync, and perform the same SELECT:
pxc1 mysql> SET SESSION wsrep_sync_wait=1;
pxc1 mysql> select * from sbtest.sbtest1 where id = 4;
What do you see ?
...
1 row in set (0.20 sec)
Put back pxc3 on dc1:
last_node_to_dc2.sh disable
162

163. Save My Data
Backups
163

164. Backups
Full: Percona XtraBackup
Feature-rich online physical Backups
Since PXC 5.6.21-25.8, There is LOCK TABLES FOR BACKUP
No FLUSH TABLES WITH READ LOCK anymore
Locks only DDL and MyISAM, leaves InnoDB fully unlocked
No more need to set the backup node in DESYNC to avoid
Flow Control
164

165. Backups
Full: Percona XtraBackup
Feature-rich online physical Backups
Since PXC 5.6.21-25.8, There is LOCK TABLES FOR BACKUP
No FLUSH TABLES WITH READ LOCK anymore
Locks only DDL and MyISAM, leaves InnoDB fully unlocked
No more need to set the backup node in DESYNC to avoid
Flow Control
Point In Time Recovery: Binary Logs
It's also recommended to save the binary logs to perform point-
in-time recovery
With mysqlbinlog 5.6, it's possible to stream them to another
'backup' host.
165

166. Backups
Full Backup
On pxc1, run the application:
run_app.sh pxc1
On pxc3, take a full backup with Percona Xtrabackup
166

167. Backups
Full Backup
On pxc1, run the application:
run_app.sh pxc1
On pxc3, take a full backup with Percona Xtrabackup
# innobackupex --galera-info --no-timestamp /root/backups/
xtrabackup version 2.2.12 based on MySQL server 5.6.24 Linux (i686) (revision id:
[01] Copying ./ibdata1 to /root/backups/ibdata1
[01] ...done
[01] Copying ./sbtest/sbtest1.ibd to /root/backups/sbtest/sbtest1.ibd
...
150920 08:31:01 innobackupex: Executing LOCK TABLES FOR BACKUP...
...
150920 08:31:01 innobackupex: Executing LOCK BINLOG FOR BACKUP...
...
150920 08:31:01 innobackupex: All tables unlocked
innobackupex: MySQL binlog position: filename 'pxc3-bin.000001',`
position 3133515
150920 08:31:01 innobackupex: completed OK!
167

168. Backups
Full Backup
Apply the logs and get the seqno:
# innobackupex --apply-log /root/backups/
# cat /root/backups/xtrabackup_galera_info
b55685a3-5f70-11e5-87f8-2f86c54ca425:1945
# cat /root/backups/xtrabackup_binlog_info
pxc3-bin.000001 3133515
We now have a full backup ready to be used.
168

169. Backups
Stream Binary Logs
Now setup mysqlbinlog to stream the binlogs in /root/binlogs.
As requirement, ensure the following is configured:
log_slave_updates
server-id=__ID__
169

170. Backups
Stream Binary Logs
Now setup mysqlbinlog to stream the binlogs in /root/binlogs.
As requirement, ensure the following is configured:
log_slave_updates
server-id=__ID__
Get mysqlbinlog running:
# mkdir /root/binlogs
# mysql -BN -e "show binary logs" | head -n1 | cut -f1
pxc3-bin.000001
# mysqlbinlog --read-from-remote-server --host=127.0.0.1
--raw --stop-never --result-file=/root/binlogs/ pxc3-bin.000001 &
170

171. Backups
Point-in-Time Recovery
On pxc2 we update a record:
pxc2 mysql> update sbtest.sbtest1 set pad = "PLAM2015" where id = 999;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
171

172. Backups
Point-in-Time Recovery
On pxc2 we update a record:
pxc2 mysql> update sbtest.sbtest1 set pad = "PLAM2015" where id = 999;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
And now it's time to break things, on pxc2, TRUNCATE the sbtest1
table.
pxc2 mysql> truncate table sbtest.sbtest1;
Query OK, 0 rows affected (0.06 sec)
172

173. Backups
Point-in-Time Recovery
BROKEN! What now?
173

174. Backups
Point-in-Time Recovery
BROKEN! What now?
Let's stop MySQL on all nodes and restore from backup.
service mysql stop
Restore the backup on pxc3:
[root@pxc3 ~]# rm -rf /var/lib/mysql/*
[root@pxc3 ~]# innobackupex --copy-back /root/backups/
[root@pxc3 ~]# chown mysql. -R /var/lib/mysql/
174

175. Backups
Point-in-Time Recovery
BROKEN! What now?
Let's stop MySQL on all nodes and restore from backup.
service mysql stop
Restore the backup on pxc3:
[root@pxc3 ~]# rm -rf /var/lib/mysql/*
[root@pxc3 ~]# innobackupex --copy-back /root/backups/
[root@pxc3 ~]# chown mysql. -R /var/lib/mysql/
On pxc3, we bootstrap a completely new cluster:
[root@pxc3 ~]# service mysql bootstrap-pxc
175

176. Backups
Point-in-Time Recovery
The full backup is restored, now we need to do point in time recovery....
Find the position of the "event" that caused the problems
176

177. Backups
Point-in-Time Recovery
The full backup is restored, now we need to do point in time recovery....
Find the position of the "event" that caused the problems
We know the sbtest.sbtest1 table got truncated. Let's find that
statement:
[root@pxc3 ~]# mysqlbinlog /root/binlogs/pxc3-bin.* | grep -i truncate -B10
OC05MzAyOTU2MDQzOC0xNzU5MDQyMTM1NS02MDYyOTQ1OTk1MC0wODY4ODc0NTg2NTCjjIc=
'/*!*/;
# at 13961536
#150920 8:33:15 server id 1 end_log_pos 13961567 CRC32 0xc97eb41f Xid = 8667
COMMIT/*!*/;
# at 13961567
#150920 8:33:15 server id 2 end_log_pos 13961659 CRC32 0x491d7ff8 Query thread_
SET TIMESTAMP=1442737995/*!*/;
SET @@session.sql_mode=1073741824/*!*/;
SET @@session.auto_increment_increment=1, @@session.auto_increment_offset=1/*!*/;
truncate table sbtest.sbtest1
177

178. Backups
Point-in-Time Recovery
We need to recover up to TRUNCATE TABLE, which was position
13961567
We can replay the binary log(s) from the last position we backupped
178

179. Backups
Point-in-Time Recovery
We need to recover up to TRUNCATE TABLE, which was position
13961567
We can replay the binary log(s) from the last position we backupped
# cat /var/lib/mysql/xtrabackup_info | grep binlog
binlog_pos = filename 'pxc3-bin.000001', position 3133515
179

180. Backups
Point-in-Time Recovery
We need to recover up to TRUNCATE TABLE, which was position
13961567
We can replay the binary log(s) from the last position we backupped
# cat /var/lib/mysql/xtrabackup_info | grep binlog
binlog_pos = filename 'pxc3-bin.000001', position 3133515
Note that if we don't have streamed the binary logs from the backup
server... it can happen, then you need to find the position from the Xid,
which is the galera seqno:
#150920 8:33:15 server id 1 end_log_pos 13961567 CRC32 0xc97eb41f Xid = 8667
COMMIT/*!*/;
# at 13961567
180

181. Backups
Point-in-Time Recovery
Let's replay it now:
# mysqlbinlog /root/binlogs/pxc3-bin.000001
--start-position=3133515 --stop-position=13961567 | mysql
181

182. Backups
Point-in-Time Recovery
Let's replay it now:
# mysqlbinlog /root/binlogs/pxc3-bin.000001
--start-position=3133515 --stop-position=13961567 | mysql
Let's Verify:
pxc3 mysql> select id, pad from sbtest.sbtest1 where id =999;
+-----+----------+
| id | pad |
+-----+----------+
| 999 | PLAM2015 |
+-----+----------+
1 row in set (0.00 sec)
182

183. Backups
Point-in-Time Recovery
Let's replay it now:
# mysqlbinlog /root/binlogs/pxc3-bin.000001
--start-position=3133515 --stop-position=13961567 | mysql
Let's Verify:
pxc3 mysql> select id, pad from sbtest.sbtest1 where id =999;
+-----+----------+
| id | pad |
+-----+----------+
| 999 | PLAM2015 |
+-----+----------+
1 row in set (0.00 sec)
You can now restart the other nodes and they will perform
SST.
183

184. Spread the load
Load Balancers
184

185. Load Balancers
With PXC a Load Balancer is commonly used:
Layer 4
Lot's of choice
Usually HAProxy (most-common)
Layer 7:
MariaDB MaxScale
ScaleArc (proprietary)
ProxySQL
mysql-proxy (beta)
185

186. Load Balancers
Usually with Galera, people uses a load balancer to route the MySQL
requests from the application to a node
Redirect writes to another node when problems happen
Mostly 1 node for writes, others for reads
Layer 4: 1 TCP port writes, 1 TCP port reads
Layer 7: Automatic (challenging)
186

187. Load Balancers
HAProxy
On pxc1, we have HA Proxy configured like this when listening on port
3308:
## active-passive
listen 3308-active-passive-writes 0.0.0.0:3308
mode tcp
balance leastconn
option httpchk
server pxc1 pxc1:3306 check port 8000 inter 1000 rise 3 fall 3
server pxc2 pxc2:3306 check port 8000 inter 1000 rise 3 fall 3 backup
server pxc3 pxc3:3306 check port 8000 inter 1000 rise 3 fall 3 backup
187

188. Load Balancers
HAProxy
On pxc2 and pxc3, we connect to the loadbalancer and run a SELECT:
mysql -h pxc1 -P 3308 -utest -ptest -e "select @@wsrep_node_name, sleep(100)"
And on pxc1 while the previous command is running we check the
processlist:
pxc1 mysql> SELECT PROCESSLIST_ID AS id, PROCESSLIST_USER AS user,
PROCESSLIST_HOST AS host, PROCESSLIST_INFO
FROM performance_schema.threads
WHERE PROCESSLIST_INFO LIKE 'select @% sleep%';
+------+------+------+-------------------------------------+
| id | user | host | PROCESSLIST_INFO |
+------+------+------+-------------------------------------+
| 294 | test | pxc1 | select @@wsrep_node_name, sleep(10) |
| 297 | test | pxc1 | select @@wsrep_node_name, sleep(10) |
+------+------+------+-------------------------------------+
188

189. Load Balancers
HAProxy
On pxc2 and pxc3, we connect to the loadbalancer and run a SELECT:
mysql -h pxc1 -P 3308 -utest -ptest -e "select @@wsrep_node_name, sleep(100)"
And on pxc1 while the previous command is running we check the
processlist:
pxc1 mysql> SELECT PROCESSLIST_ID AS id, PROCESSLIST_USER AS user,
PROCESSLIST_HOST AS host, PROCESSLIST_INFO
FROM performance_schema.threads
WHERE PROCESSLIST_INFO LIKE 'select @% sleep%';
+------+------+------+-------------------------------------+
| id | user | host | PROCESSLIST_INFO |
+------+------+------+-------------------------------------+
| 294 | test | pxc1 | select @@wsrep_node_name, sleep(10) |
| 297 | test | pxc1 | select @@wsrep_node_name, sleep(10) |
+------+------+------+-------------------------------------+
What do you notice ?
189

190. Load Balancers
HA Proxy & Proxy Protocol
Since Percona XtraDB Cluster 5.6.25-73.1 we support proxy
protocol! (Almost released)
190

191. Load Balancers
HA Proxy & Proxy Protocol
Since Percona XtraDB Cluster 5.6.25-73.1 we support proxy
protocol! (Almost released)
Let's enable this in my.cnf on all 3 nodes:
[mysqld]
...
proxy_protocol_networks=*
...
191

192. Load Balancers
HA Proxy & Proxy Protocol
Since Percona XtraDB Cluster 5.6.25-73.1 we support proxy
protocol! (Almost released)
Let's enable this in my.cnf on all 3 nodes:
[mysqld]
...
proxy_protocol_networks=*
...
Restart them one by one:
[root@pxc1 ~]# /etc/init.d/mysql restart
...
[root@pxc2 ~]# /etc/init.d/mysql restart
...
[root@pxc3 ~]# /etc/init.d/mysql restart
192

193. Load Balancers
HA Proxy & Proxy Protocol
On pxc1, we have HAProxy configured like this when listening on port
3310 to support proxy protocol:
listen 3310-active-passive-writes 0.0.0.0:3310
mode tcp
balance roundrobin
option httpchk
server pxc1 pxc1:3306 send-proxy-v2 check port 8000 inter 1000 rise 3 fall 3
server pxc2 pxc2:3306 send-proxy-v2 check port 8000 inter 1000 backup
server pxc3 pxc3:3306 send-proxy-v2 check port 8000 inter 1000 backup
And restart HAProxy:
service haproxy restart
193

194. Load Balancers
HA Proxy & Proxy Protocol
On pxc2 and pxc3, we connect to the loadbalancer (using the new
port) and run a SELECT:
mysql -h pxc1 -P 3310 -utest -ptest -e "select @@wsrep_node_name, sleep(10)"
And on pxc1 while the previous command is running we check the
processlist:
pxc1 mysql> SELECT PROCESSLIST_ID AS id, PROCESSLIST_USER AS user,
PROCESSLIST_HOST AS host, PROCESSLIST_INFO
FROM performance_schema.threads
WHERE PROCESSLIST_INFO LIKE 'select @% sleep%';
+------+------+------+-------------------------------------+
| id | user | host | PROCESSLIST_INFO |
+------+------+------+-------------------------------------+
| 75 | test | pxc2 | select @@wsrep_node_name, sleep(10) |
| 76 | test | pxc3 | select @@wsrep_node_name, sleep(10) |
+------+------+------+-------------------------------------+
194

195. Load Balancers
HA Proxy & Proxy Protocol
Try to connect from pxc1 to pxc1, not using a load balancer:
pxc1 # mysql -h pxc1 -P 3306
What happens?
195

196. Load Balancers
HA Proxy & Proxy Protocol
Try to connect from pxc1 to pxc1, not using a load balancer:
pxc1 # mysql -h pxc1 -P 3306
What happens?
You can't connect to mysql anymore.
When proxy_protocol_network is enabled it won't connect if you
don't send TCP proxy header!
196

197. Load Balancers
HA Proxy & Proxy Protocol
Try to connect from pxc1 to pxc1, not using a load balancer:
pxc1 # mysql -h pxc1 -P 3306
What happens?
You can't connect to mysql anymore.
When proxy_protocol_network is enabled it won't connect if you
don't send TCP proxy header!
Let's cleanup the proxy_protocol_network and restart all nodes
before continuing.
197