Percona Xtradb Cluster (pxc) 101 percona university 2019
- 1. © 2019 Percona1 Marcelo Henrique Gonçalves Percona XtraDB Cluster (PXC) 101 Introduction to Percona XtraDB Cluster and some features. Managed Services MySQL DBA @ Percona Percona University São Paulo 27/04/2019
- 2. © 2019 Percona2 Percona XtraDB Cluster (PXC) 101 This presentation is based on a Webinar: Percona XtraDB Cluster (PXC) 101 by Krunal Bauskar. ▪The PXC and the world • Introduction to the software and it’s way of replication • Limitations? • Is it usable for HA? ▪Exclusive features in PXC compared to Galera/MariaDB
- 3. © 2019 Percona3 Agenda ● Common ways to replicate data ● Ways of replicating async ● Synchronous Replication ● PXC ● How PXC replicates ● Limitations of PXC ● Some Features (5.7) ● HA solution using PXC
- 4. © 2019 Percona4 Common ways to replicate data ● Replication built-in in MySQL, MariaDB or Percona Server: Binlog (GTID or not). ● Either ASYNChronous or SEMI-SYNChronous (not counting with NDB Cluster Synchronous replication). ● Asynchronous is that writes will be done in a replica without impacting master and application commit only guarantees data in the Master, not replica.
- 5. © 2019 Percona5 Common ways to replicate data In my point of view: ● Semi-synchronous is just a nice name for Asynchronous. ● If the master loses connectivity with slave, it will keep allowing writes.
- 6. © 2019 Percona6 Ways of replicating async
- 7. © 2019 Percona7 Ways of replicating async
- 8. © 2019 Percona8 Ways of replicating async + Creativity = Several Topologies
- 9. © 2019 Percona9 Ways of replicating async ● Replication delay (possible loss of transactions). Not rarely, relaxed durability is used - sync_binlog. ● Ok read scalability - subject to high data latency. ● No horizontal write-scalability. ● Switchover interval, even being small. ● No protection against network failure. ● Master + Master = Can be dangerous
- 10. © 2019 Percona10 Synchronous Replication We can’t get rid of CAP theorem BUT we can have: ● All nodes open for read/write (1) ● Great scalability in read ● No single point of failure - Tightly coupled ● Easy to maintain/deploy - Automatic Node Provisioning ● Protect against network outages (2) ● All nodes as an active master (3) 1 - Multithreaded replication limited to slower node and network latency. 2 - Partial network outages, subject to Quorum 3 - Avoid same table write in multiple nodes
- 11. © 2019 Percona11 PXC ● PXC - multi-master solution with Percona Server ● Galera plugin - from Codeship ● Percona product -> independent and has complete life cycle. 1. Consistency 2. Availability 3. Partition Tolerance
- 12. © 2019 Percona12 PXC ● Write to any node(1) ● Read from any node ● CURRENT(2) AND CONSISTENT 1 Subject to deadlocks, first committer wins, speed of slower node 2 Subject to <fc_limit> number of write sets.
- 13. © 2019 Percona13 PXC Can be used in many different topologies.
- 14. © 2019 Percona14 PXC - enterprise ready ● Automatic Node Provisioning ● Ability to handle conflicting workload ● Tunable flow control ● Parallel Processing ● Protection against network failure ● Can be Geo-distributed ● Cluster safe-mode ● Security ● Performance ● Trackability - easy troubleshoot
- 15. © 2019 Percona15 How PXC replicates - Certification Based Layer 1: Percona Server (Write-set) Layer 2: Galera Plugin Layer 3: gcomm communication channel Write-sets are written in GALERA CACHE (a file in each node) Source: http://galeracluster.com/documentation-webpages/certificationbasedreplication.html Copyright: 2014 Codership Ltd.
- 16. © 2019 Percona16 How PXC replicates - Steps SST + IST ● First node needs bootstrap (systemctl start mysql@bootstrap) ● The node that starts with the bootstrap is the source of truth. ● A new node will run SST - State Snapshot Transfer (mysqldump/rsync/xtrabackup) ● Any existing data in next node is erased, a new full backup is restored and it is started - joining the cluster. ● New node perform Incremental State Transfer - IST ● Reads galera cache from donor, and apply. ● New node is now synced with cluster. ● New node is Writable. Understanding how an IST donor is selected
- 17. © 2019 Percona17 How PXC replicates - Steps IST 1. Node 1 goes down - and starts again and join the cluster 2. Node 1 needs write-set starting from 14015 (already considering safe gap). 3. Node 2 galera cache has 14020, Node 3 galera cache has 13400 4. Node 1 SELECT node 2 as IST donor - Node 1 is YET not usable 5. Node 1 receives write-sets and apply - IST 6. Node 1 gets in sync and enabled Read Write again. ● If there is no node with galera cache old enough, a SST is done by Node 1. ● Can be avoided with gcache.freeze_purge_at_seqno Sample case:
- 18. © 2019 Percona18 How PXC replicates - workload ● Optimistic Lock - no distributed locks ● First committer win. ● Conflicting transaction forceful abort ● Certification Failure - can’t allow 2 conflicting transactions. ● Flow control dynamically controlled. * Transactions are queued - queue full triggers flow control Image by Krunal Bauskar
- 19. © 2019 Percona19 How PXC replicates - Parallel processing ● Parallel worker threads - works without collisions ● Coordinated to allow first commit win ● Online tunnable ● Low resources consumption ● Threads visible in processlist ● Only 1 rollback thread
- 20. © 2019 Percona20 How PXC replicates - Quorum ● By default, each node votes 1 - Quorum is total of votes ● Votes online needs to be ½ +1 of total Cluster (talking to each other) Cluster of 3 -> 2 up Cluster of 4 -> 3 up Cluster of 5 -> 3 up Cluster of 6 -> 4 up ● Auto-recovery - Once nodes are back online -> join/sync ● Network variables configurable for different timeouts ● Protection against Split-Brain ● Geo distributed - with ‘DC awareness’ variable (gmcast.segment) ● Ability to have Arbitrator node - A node without data that only votes
- 21. © 2019 Percona21 Limitations of PXC ● Works only with InnoDB ● Can’t use Lock tables, Unlock tables, GET_LOCK(), RELEASE_LOCK(), and similar ● Can’t log queries to table - log_output = FILE ● There is a limit for transactions size - LOAD DATA will commit every 10k rows ● Transaction can fail at commit stage ● XA transactions can’t be used ● Write throughput limited to slower node ● InnoDB fake changes feature not supported ● DELETE in tables without Primary Key not supported Among other small ones in: https://www.percona.com/doc/percona-xtradb-cluster/LATEST/limitation.html
- 22. © 2019 Percona22 If workload that is not cluster safe: pxc_strict_mode acts: ENFORCING MASTER PERMISSIVE DISABLED Cluster Safe Mode Image by Krunal Bauskar
- 23. © 2019 Percona23 ● Compatible with At Rest tablespace encryption - 5.7 ● SST + IST - can be done in encrypted channels ● Replication traffics - can be encrypted as well ● ALL security from PS applies! Security
- 24. © 2019 Percona24 ● Industry lead performance solution (5.7.17+) ● Fit several workloads - OLTP/POINT UPDATE/WH ... ● Quicker Node rejoins ● All Percona Server tuning ● Allow a Node to be Desync ● Allow a Node in Maintenance Performance
- 25. © 2019 Percona25 ● TRACK Node behavior in the cluster (delaying ot being delayed) ● Overload of replication replicas or network ● show status (Flow-control, IST progress, queue size, replication latency, applied/committed upto, cache size) ● performance_schema.pxc_cluster_view ● Other internal objects exposed through Perf. Schema (PFS) ● Clear error/information logs ● Improved debugging messages for SST ● Improved visibility of thread state through show processlist Performance - Trackability
- 26. © 2019 Percona26 Complete HA solution should have: ● Stable cluster ● Load Balance ● Simplified and Unified view of the system ● Easy/Quick Failover / Switchover ● Easy Business Continuity Solution HA Solution using PXC
- 27. © 2019 Percona27 ● PXC can operate with multiple load/setups ● Balancers like HAProxy, ProxySQL, etc... PXC suggests use of ProxySQL ● Integrated and closed development. ● Feature rich load balancer (lot more features getting added) ● Custom PXC script aids simplified PXC configuration (auto-discovery of PXC nodes). HA - Load Balancer
- 28. © 2019 Percona28 PXC maintenance mode ● Abrupt graceful shutdown can cause disruption in workload till Load-Balancer adjust the load/connections. ● Maintenance mode is like advance warning helping load balancer (ProxySQL only) to make a note of this and pre-adjust workload. ● Also applicable if node needs to stop active traffic for maintenance purpose. ● In 5.7.16 - pxc_maint_transition_period tempo de transição dos estados (10s padrão) HA - Load Balancer
- 29. © 2019 Percona29 PMM - complete dashboard ● PMM (Percona Monitoring and Management) ● Complete integrated with PXC ● Simple way to take control of complete HA system https://pmmdemo.percona.com/ SIMPLIFIED AND UNIT VIEW OF THE CLUSTER SYSTEM
- 30. © 2019 Percona30 Complete HA solution should have: ● Stable cluster ● Load Balance ● Simplified and Unified view of the system ● Easy/Quick Failover / Switchover ● Easy Business Continuity Solution PXC as complete HA solution
- 31. © 2019 Percona31 PXC forum https://www.percona.com/forums/questions-discussions/percona-xtradb-cluster PXC @ JIRA https://jira.percona.com/projects/PXC/issues PXC Webinar 101 - Questions and Answers PXC QUIZ Reference: Percona XtraDB Cluster (PXC) 101 by Krunal Bauskar QUESTIONS / PERGUNTAS Keep research / Keep Contact marcelo.goncalves@percona.com Twitter: @billmask LinkedIn: https://www.linkedin.com/in/billmask/
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