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PostgreSQL Replication - Second Edition
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Information
PostgreSQL Replication Second Edition
Table of Contents
PostgreSQL Replication Second Edition
Credits
About the Author
About the Reviewers
www.PacktPub.com
Support files, eBooks, discount offers, and more
Why subscribe?
Free access for Packt account holders
Preface
What this book covers
What you need for this book
Who this book is for
Conventions
Reader feedback
Customer support
Errata
Piracy
Questions
1. Understanding the Concepts of Replication
The CAP theorem and physical limitations of replication
Understanding the CAP theorem
Understanding the limits of physics
Different types of replication
Synchronous versus asynchronous replication
Considering performance issues
Understanding replication and data loss
Single-master versus multimaster replication
Logical versus physical replication
When to use physical replication
When to use logical replication
Using sharding and data distribution
Understanding the purpose of sharding
Designing a sharded system
Querying different fields
Pros and cons of sharding
Choosing between sharding and redundancy
Increasing and decreasing the size of a cluster
Combining sharding and replication
Various sharding solutions
PostgreSQL-based sharding
Summary
2. Understanding the PostgreSQL Transaction Log
How PostgreSQL writes data
The PostgreSQL disk layout
Looking into the data directory
PG_VERSION – the PostgreSQL version number
base – the actual data directory
Growing data files
Performing I/O in chunks
Relation forks
global – the global data
Dealing with standalone data files
pg_clog – the commit log
pg_dynshmem – shared memory
pg_hba.conf – host-based network configuration
pg_ident.conf – ident authentication
pg_logical – logical decoding
pg_multixact – multitransaction status data
pg_notify – LISTEN/NOTIFY data
pg_replslot – replication slots
pg_serial – information about committed serializable transactions
pg_snapshot – exported snapshots
pg_stat – permanent statistics
pg_stat_tmp – temporary statistics data
pg_subtrans – subtransaction data
pg_tblspc – symbolic links to tablespaces
pg_twophase – information about prepared statements
pg_xlog – the PostgreSQL transaction log (WAL)
postgresql.conf – the central PostgreSQL configuration file
Writing one row of data
A simple INSERT statement
Crashing during WAL writing
Crashing after WAL writing
Read consistency
The purpose of the shared buffer
Mixed reads and writes
The format of the XLOG
The XLOG and replication
Understanding consistency and data loss
All the way to the disk
From memory to memory
From the memory to the disk
A word about batteries
Beyond the fsync function
PostgreSQL consistency levels
Tuning checkpoints and the XLOG
Understanding the checkpoints
Configuring the checkpoints
Segments and timeouts
To write or not to write?
Scenario 1 – storing stock market data
Scenario 2 – bulk loading
Scenario 3 – I/O spikes and throughput considerations
Conclusion
Tweaking WAL buffers
Experiencing the XLOG in action
Understanding the XLOG records
Making the XLOG deterministic
Making the XLOG reliable
LSNs and shared buffer interaction
Debugging the XLOG and putting it all together
Making use of replication slots
Physical replication slots
Logical replication slots
Configuring replication identities
Summary
3. Understanding Point-in-time Recovery
Understanding the purpose of PITR
Moving to the bigger picture
Archiving the transaction log
Taking base backups
Using pg_basebackup
Modifying pg_hba.conf
Signaling the master server
pg_basebackup – basic features
Backup throttling
pg_basebackup – self-sufficient backups
Making use of traditional methods to create base backups
Tablespace issues
Keeping an eye on the network bandwidth
Replaying the transaction log
Performing a basic recovery
More sophisticated positioning in the XLOG
Cleaning up the XLOG on the way
Switching the XLOG files
Summary
4. Setting Up Asynchronous Replication
Setting up streaming replication
Tweaking the config files on the master
Handling pg_basebackup and recovery.conf
Making the slave readable
The underlying protocol
Configuring a cascaded replication
Turning slaves into masters
Mixing streaming-based and file-based recovery
The master configuration
The slave configuration
Error scenarios
Network connection between the master and slave is dead
Rebooting the slave
Rebooting the master
Corrupted XLOG in the archive
Making streaming-only replication more robust
Using wal_keep_segments
Utilizing replication slots
Efficient cleanup and the end of recovery
Gaining control over the restart points
Tweaking the end of your recovery
Conflict management
Dealing with timelines
Delayed replicas
Handling crashes
Summary
5. Setting Up Synchronous Replication
Synchronous replication setup
Understanding the downside to synchronous replication
Understanding the application_name parameter
Making synchronous replication work
Checking the replication
Understanding performance issues
Setting synchronous_commit to on
Setting synchronous_commit to remote_write
Setting synchronous_commit to off
Setting synchronous_commit to local
Changing durability settings on the fly
Understanding the practical implications and performance
Redundancy and stopping replication
Summary
6. Monitoring Your Setup
Checking your archive
Checking archive_command
Monitoring the transaction log archive
Checking pg_stat_replication
Relevant fields in pg_stat_replication
Checking for operating system processes
Checking for replication slots
Dealing with monitoring tools
Installing check_postgres
Deciding on a monitoring strategy
Summary
7. Understanding Linux High Availability
Understanding the purpose of High Availability
Measuring availability
Durability and availability
Detecting failures
The split-brain syndrome
Understanding Linux-HA
Corosync
Pacemaker
Resource agents / fence agents
PCS
The PostgreSQL resource agent
Setting up a simple HA cluster
Preparing the servers
Installing the necessary software
Configuring the clustering software
Preparing for the PostgreSQL installation
Syncing the standby
Configuring the cluster
Configuring cluster resources
Configuring the constraints
Setting up fencing
Verifying the setup
Common maintenance tasks
Performing maintenance on a single node
Forcing a failover
Recovering from failed PostgreSQL starts
Performing cluster-wide maintenance
Resynchronizing after master failure
Summary
8. Working with PgBouncer
Understanding the fundamental PgBouncer concepts
Installing PgBouncer
Configuring your first PgBouncer setup
Writing a simple config file and starting PgBouncer up
Dispatching requests
More basic settings
Handling pool sizes
max_client_conn
default_pool_size
min_pool_size
res...
Table of contents
- PostgreSQL Replication Second Edition