This document discusses best practices for high availability (HA) and replication of PostgreSQL databases in virtualized environments. It covers enterprise needs for HA, technologies like VMware HA and replication that can provide HA, and deployment blueprints for HA, read scaling, and disaster recovery within and across datacenters. The document also discusses PostgreSQL's different replication modes and how they can be used for HA, read scaling, and disaster recovery.

1. Best Practices for HA and Replication for
PostgreSQL in Virtualized Environments
March 2013 Jignesh Shah & vPostgres Team @ VMware
© 2010 VMware Inc. All rights reserved

2. Agenda
§ Enterprise needs
§ Technologies readily available
• Virtualization Technologies for HA
• Replication modes of PostgreSQL (in core)
§ Datacenter Deployment Blueprints
• HA within Datacenter,
• Read-Scaling within Datacenter
• DR/Read-Scaling across Datacenters
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3. Enterprise Needs for
Mission Critical Databases
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4. Causes of Downtime
§ Planned Downtime
• Software upgrade (OS patches, SQL Server cumulative updates)
• Hardware/BIOS upgrade
§ Unplanned Downtime
• Datacenter failure (natural disasters, fire)
• Server failure (failed CPU, bad network card)
• I/O subsystem failure (disk failure, controller failure)
• Software/Data corruption (application bugs, OS binary corruptions)
• User Error (shutdown a SQL service, dropped a table)
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5. Enterprises need HA
§ HA - High Availability of the Database Service
• Sustain Database Service failure if it goes down
• Sustain Physical Hardware Failures
• Sustain Data/Storage Failures
• 100% Data Guarantee
§ Goal
• Reduce Mean Time To Recover (MTTR) or Recovery Time Objective (RTO)
• Typically driven by SLAs
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6. Planning a High Availability Strategy
§ Requirements
• Recovery Time Objective (RTO)
• What does 99.99% availability really mean?
• Recovery Point Objective (RPO)
• Zero data lost?
• HA vs. DR requirements
§ Evaluating a technology
• What’s the cost for implementing the technology?
• What’s the complexity of implementing, and managing the technology?
• What’s the downtime potential?
• What’s the data loss exposure?
Availability %
Downtime / Year
Downtime / Month *
Downtime / week
"Two Nines" - 99%
3.65 Days
7.2 Hours
1.69 Hours
"Three Nines" - 99.9%
8.76 Hours
43.2 Minutes
10.1 Minutes
"Four Nines" - 99.99%
52.56 Minutes
4.32 Minutes
1.01 Minutes
"Five Nines" - 99.999%
5.26 Minutes
25.9 Seconds
6.06 Seconds
* Using a 30 day month
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7. Enterprises need DR
§ DR – Disaster Recovery for your site
• Overcome Complete Site Failure
• Closest if not 100% Data Guarantee expected
• Some data loss may be acceptable
• Key Metrics
• RTO – Recovery Time Objective
• Time to Recover the service
• RPO – Recovery Point Objective
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8. Enterprises also need Scale UP
§ Scale UP – Throughput increases with more resources given in the
same VM
§ Though in reality limited by Amdahl’s law
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9. Enterprises also need Scale Out
§ Scale Out – Throughput increases with more resources given via
more nodes (VMs)
§ Typically Shared Nothing architecture (few Shared ‘something’)
§ Often results in “partitions” or “shards”
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10. Scale Out - For Reads
§ Scale Out or Multi-Node Scaling for Reads
§ Online retailer Use Case
§ 99% Reads and 1% Actual Write transactions
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11. Scale Out - For Writes
§ Scale Out or Multi-nodes for Writes
§ Example Use case: 24/7 Booking system
§ Constant booking/changes/updates happening
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12. CAP Theorem
§ Consistency
• all nodes see the same data at the same time
§ Availability
• Guarantee that every request receives a response about whether it was
successful or failed
§ Partition Tolerance
• the system continues to operate despite arbitrary message loss or failure of
part of the system
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13. Virtualization Technologies for HA
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14. Virtualization Availability Features
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15. VM Mobility
§ Server Maintenance
• VMware vSphere® vMotion® and
VMware vSphere Distributed
Resource Scheduler (DRS)
Maintenance Mode
• Migrate running VMs to other
servers in the pool
• Automatically distribute workloads
for optimal performance
Key Benefits
§ Storage Maintenance • Eliminate downtime for common
maintenance
• VMware vSphere® Storage vMotion
• No application or end user impact
• Migrate VM disks to other storage
targets without disruption • Freedom to perform maintenance
whenever desired
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16. VMware vSphere High Availability (HA)
§ Protection against host or operating system failure
• Automatic restart of virtual machines on any available host in cluster
• Provides simple and reliable first line of defense for all databases
• Minutes to restart
• OS and application independent, does not require complex configuration
or expensive licenses
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17. App-Aware HA Through Health Monitoring APIs
§ Leverage third-party solutions that integrate with VMware HA
(for example, Symantec ApplicationHA)
1
Database Health Monitoring
VMware HA • Detect database service failures inside VM
App
Restart 3
2
2 APP APP
Database Service Restart Inside VM
OS OS
• App start / stop / restart inside VM
1 • Automatic restart when app problem detected
3
Integration with VMware HA
• VMware HA automatically initiated when
• App restart fails inside VM
• Heartbeat from VM fails
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18. Simple, Reliable DR with VMware SRM
§ Provide the simplest and most reliable disaster protection and site
migration for all applications
§ Provide cost-efficient replication of applications to failover site
§ Simplify management of recovery and migration plans
§ Replace manual run books with centralized recovery plans
§ From weeks to minutes to set up new plan
§ Automate failover and migration
processes for reliable recovery
§ Provide for fast, automated failover
§ Enable non-disruptive testing
§ Automate failback processes
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19. High Availability Options through Virtualization Technologies
PostgreSQL
Streaming
Hardware Failure Tolerance
Replication
Continuous
VMotion
VMware FT
Automated (Planned Downtime)
Restart
RedHat/OS Cluster
VMware HA
Unprotected
0% 10% 100%
Application Coverage
§ Clustering too complex and expensive for most applications
§ VMware HA and FT provide simple, cost-effective availability
§ VMotion provides continuous availability against
planned downtime
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20. PostgreSQL
Replication Modes
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21. PostgreSQL Replication
§ Single master, multi-slave
§ Cascading slave possible with vFabric Postgres 9.2
§ Mechanism based on WAL (Write-Ahead Logs)
§ Multiple modes and multiple recovery ways
• Warm standby
• Asynchronous hot standby
• Synchronous hot standby
§ Slaves can perform read operations optionally
• Good for read scale
§ Node failover, reconnection possible
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22. File-based replication
§ File-based recovery method using WAL archives
§ Master node sends WAL files to archive once completed
§ Slave node recovers those files automatically
§ Some delay for the information recovered on slave
• Usable if application can lose some data
• Good performance, everything is scp/rsync/cp-based
• Timing when WAL file is sent can be controlled
vPG
ile slave 1
WAL file WAL f
vPG
master
WAL Archive
disk vPG
slave 2
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23. Asynchronous replication
§ WAL record-based replication
§ Good balance performance/data loss
• Some delay possible for write-heavy applications
• Data loss possible if slaves not in complete sync due to delay
§ Possible to connect a slave to a master or a slave (cascading
mode)
vPG Slave 1 Slave 1-1
master
WAL shipping
Slave 2 Slave 1-2
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24. Synchronous mode
§ COMMIT-based replication
• Only one slave in sync with master
• Master waits that transaction COMMIT happens on sync slave, then commits
§ No data loss based on transaction commit
• Performance impact
• Good for critical applications
§ Cascading slaves are async
async
vPG Slave 1 Slave 1-1
master
WAL shipping
Slave 2 Slave 1-2
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25. HA operations: failover and node
reconnection
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26. Node failover (1)
§ Same procedure for all the replication modes
vPG
Slave
master
§ Failover procedure
Promotion
• Connect to slave VM
ssh postgres@$SLAVE_IP
• Promote the slave
pg_ctl promote
• recovery.conf renamed to recovery.done in $PGDATA
• Former slave able to run write queries
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27. Node failover (2)
§ Locate archive disk to a new slave node
• Recreate new virtual disk on new node
• Update restore_command in recovery.conf of the remaining slaves
• Update archive_command in postgresql.conf of promoted slave
• Copy WAL files from remaining archive disk to prevent SPOF after loss of
master
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28. Node reconnection
§ In case a previously failed node is up again
old
Promoted
master
Slave
Reconnect
§ Reconnection procedure
• Connect to old master VM
ssh postgres@$MASTER_IP
• Create recovery.conf depending on recovery mode wanted
recovery_target_timeline = ‘latest’
standby_mode = on
restore_command = ’scp $SLAVE_IP:/archive/%f %p’
primary_conninfo = 'host=$SLAVE_IP application_name=$OLD_NAME’
• Start node
service postgresql start
• Important! Retrieving WAL is necessary for timeline switch
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29. Additional tips
§ DB and server UI
• Usable as normal, cannot create objects on slave of course
§ wal_level
• ‘archive’ for archive only recovery
• ‘hot_standby’ for read-queries on slaves
§ pg_stat_replication to get status of connected slaves
postgres=# SELECT pg_current_xlog_location(),
application_name,
sync_state,
flush_location
FROM pg_stat_replication;
pg_current_xlog_location | application_name | sync_state | flush_location
--------------------------+------------------+------------+----------------
0/5000000 | slave2 | async | 0/5000000
0/5000000 | slave1 | sync | 0/5000000
(2 rows)
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30. Virtualized PostgreSQL
Datacenter Deployment
Blueprints
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31. Single Data Center Deployment
Highly Available PostgreSQL database server with HA from virtualization environment
DNS Name
Applications
Site 1
§ Easy to setup with one click HA
§ Handles CPU/Memory hardware issues
§ Requires Storage RAID 1 for storage protection (atleast)
§ RTO in couple of minutes
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32. vSphere HA with PostgreSQL 9.2 Streaming Replication)
§ Protection against HW/SW failures and DB corruption
§ Storage flexibility
(FC, iSCSI, NFS)
§ Compatible w/ vMotion,
DRS, HA
§ RTO in few seconds
§ vSphere HA + Streaming Replication
• Master generally restarted with vSphere HA
• When Master is unable to recover, the Replica can be promoted to master
• Reduces synchronization time
after VM recovery
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33. Single Data Center Deployment
Highly Available PostgreSQL database server with synchronous replication
Virtual IP or
DNS or
pgPool or
Applications
pgBouncer
Site 1
§ Synchronous Replication within Data Center
§ Low Down Time (lower than HA)
§ Automated Failover for hardware issues including Storage
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34. Multi-site Data Center Deployment
Replication across Data Centers with PostgreSQL for Read Scaling/DR
Applications Virtual IP or
Site 2
pgPool or
pgBouncer
Site 1
§ Synchronous Replication within Data Center
§ Asynchronous replication across data enters
§ Read Scaling (Application Driver ) Site 3
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35. Multi-site Data Center Deployment
Replication across Data Centers with Write Scaling (requires sharding)
Applications Virtual IP or
Site 2
pgPool or
pgBouncer
Site 1
§ Each Site has its own shard, its synchronous replica and
asynchronous replicas of other sites
§ Asynchronous replication across data enters
Site 3
§ HA/DR built-in
§ Sharding is application driven
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36. Hybrid Cloud
Hybrid Cloud Scaling for Fluctuating Read peaks
Virtual IP or
pgPool or
pgBouncer
Applications
Site 1
Cascaded
Read
Replicas
§ Many times reads go up to 99% of workload
§ (Example a sensational story that every one wants to read)
§ Synchronous Replication within Data Center
§ Asynchronous Replica slaves within Data Center and on Hybrid Clouds
§ More replicas are spun up when load increases and discarded when it decreases
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37. Summary
PostgreSQL 9.2 Future /Others
• Database Replication • BiDirectional Replication
• Synchronous
• Asynchronous • Slony/Londiste, etc
• Log Shipping
Virtualization Platform
Un-Planned downtime recovery Disaster recovery
• vSphere HA + AppAware HA • Site Recovery Manager
• vSphere FT
Planned downtime avoidance
• vMotion & Storage vMotion
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38. Your Feedback is Important!
If interested,
§ Drop your at end of session
§ Email: jshah@vmware.com
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39. Thanks.
Questions?
Follow us on twitter: @vPostgres
vFabric Blog: http://blogs.vmware.com/vfabric/postgres
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