This presentation deals with the various SST methods in Percona XtraDB Cluster and MariaDB Cluster.

1. Kabilesh P R
Co-Founder, Mydbops
May 22nd, 2021
Mydbops Webinar 5
State Transfers With Galera

2. Interested in Open Source technologies
Building Solutions on MySQL, Cloud & MongoDB
Active Tech Speaker/Blogger
AWS community Builder
Co-Founder, Mydbops
Kabilesh PR
About Me

3. Consulting
Services
Managed
Services
Focuses on Top Opensource database MySQL,
MongoDB and PostgreSQL
Mydbops Services

4. 400 + Clients In 4 Yrs. of Operations
Our Clients

5. Agenda
What is Galera ?
Highlights
State transfers

6. Galera .....

7. Open source replication plugin for synchronous and multi master
replication
Read and write can be made on any node
No complex failover solutions
What is Galera?
WSREP (Write Set REPlication) is an API to connect the Galera
library and control the characteristics of Galera
Implement Certificate based replication and multi master
replication

8. Galera replication
Node 3
Node 1 Node 2

9. Highlights .....

10. (State Transfer)
Synchronous Replication ( Virtually )
Parallel applier threads
Quorum based
Automatic node provisioning
Multi master writes

11. What is a state transfer ?
State transfer is a way in which the nodes in
clusters connect with each other and transfer
states(data) with each other to come in sync
with each other

12. When is state transfer needed ?
Network partitions
Node failures
Planned Maintanence
Node addition
Manual state transfers
Human err
Software failures (bug)

13. Transfer Methods
IST (Incremental State Transfer)
SST (State Snapshot Transfer)
Ports:
IST - 4568
SST - 4444

14. Incremental State transfer (IST)
As the name indicates it sync back with the incremental changes
from the last seen sequence number of its own(grastate.dat)
Gcache aka Ring Buffer files stores the recent write-set, based
on its size default 128MB
Larger the size of Gcache greater the chances for IST
IST less intrusive and fastest way of joining the node back to
group

15. Incremental State transfer (IST)
Node 1 Node 2
Donor
Joiner
Grastate.dat
Gcache
Gcache
Request to join
Seq.no=n+m
GTID: Seq.no
GroupID: Seqno
Seq.no=n

16. Node 1 Node 2
Donor
Joiner
Gcache Gcache
Seq.no=n+m
}
Send IST Events
Grastate.dat
Apply
GroupID: Seqno
Incremental State transfer (IST)

17. State Snapshot Transfer (SST)
State Snapshot Transfer (SST) is a way for Galera to
transfer a full data copy from an existing node (donor) to
a new node (joiner)
SST is slow and high performance impacting process
SST Method:
Mysqldump
RSYNC
Xtrabackup/Mariabackup
Clone(8.0.22)
Logical Transfer
Physical Transfer

18. Logical Transfer - Mysqldump
Least preferred method of state transfer because of the slowness(dump
restore)
Cause locking in Donor node
Independent of the environment comparing to other methods
Requires the receiving node to have a fully functional database
Needs root creds same as donor and accessibility
Work well for smaller dataset

19. Physical State Transfer
Transfers physical copy from donor to joiner
No working DB is needed, overwrites disk in joiner node
Physical transfers are usally faster(network)
Depends on the physical layout such as disk,storage engine

20. SST Method - RSYNC
Uses rsync method for physical transfer
Blocks the donor during copy
Donot require root DB access
Ability to have only change data copy with rsync-wan
(delta transfer algorithm)
Recommended to have same version at both ends
wsrep_sst_method = RSYNC

21. SST Method - Xtrabackup
Most recommended and popular method
Virtually non-blocking on donor except for MyISAM table
Resource utilisation may go high in donor
Recommended to have exact same version in source
and destination
wsrep_sst_auth = <wsrep_sst_user>:<password>
wsrep_sst_method = xtrabackup

22. SST Method - Clone
Available from 8.0.22 mysql and 10.5 Mariadb
Based on native clone plugin introduced in 8.0.17
Much faster than xtrabackup
Blocks donor on DDL
wsrep_sst_method=clone
wsrep_sst_auth=<admin user>:<admin password>

23. SST Methods comparision

24. Node2
Node1 Joiner
Application Application
Group Communication channel
SST Request
Wsrep_sst_method
Node request to Join

25. Node1 Donor
Joiner
Group Communication channel
Application Application
RSYNC
Xtrabackup
Clone
State Snapshot Transfer

26. SST Methods - Summary
Method Speed Blocks Donor Node Avail Type Root Access
mysqldump slow Blocks Available Logical
Donor and
Joiner
Rsync Faster Blocks Unavailable Physical None
Xtrabackup Fast Briefly Unavailable Physical Only Donor
Clone Fastset On DDL Unavailable Physical Only Donor

27. Reach Us : Info@mydbops.com
Thank You