rubyrep Database replication that doesn’t hurt.
Unlike Oracle & MySQL : PostgreSQL doesn’t’ have built in replication solutions but there are many other replication solutions available for PostgreSQL liked listed here :-
and some additional proprietary solutions for the custom needs by different companies.
Mostly people use Slony : http://www.slony.info/ for master – slave replication solution – Slony is a “master to multiple slaves” replication system supporting cascading (e.g. – a node can feed another node which feeds another node…) and failover.
but Slony has limitations as mentioned here :
- Replicated tables must have a unique or primary key
- It does not support replication of large objects
- Schema changes are not propagated (though they can be coordinated)
- It does not support synchronizing databases outside of replication
- There are limitations on version compatibility; you can not replicate from PostgreSQL 8.2 to PostgreSQL 8.4 for example
- It is more difficult to set up than many other replication solutions
There are many new replication and clustering solutions being there but most of them in development phases only.
To provide mater-master replication in PostgreSQL – mostly used solutions are :-
and RubyRep is most easy to setup and configure.
Development of an open-source solution for asynchronous, master-master replication of relational databases that is
- ridiculously easy to use
- database independent
RubyRep always operates on two databases. To make it simple to understand, the databases are referred to as “left” and “right” database respectively.
RubyRep’s key features includes:
- Simple configuration, complete setup can be done via single configuration file.
- Simple Installation, if you have a JVM installed, then you just have to download and extract the files.
- Platform Independent, it runs on Unix and Windows platform.
- Table Design Independent, meaning that all commands work on tables no matter if they have a simple primary key (all data types acceptable), a combined primary key, or no primary key at all. It successfully processes multi-byte texts and “big” data types
- It replicates tsvector datatype
In addition to the above, RubyRep actually provides three tools in one; a Compare, Sync, and Replication tools.
This tool scans corresponding tables of left and right database, looking for diverging data. Key features of the comparison tool are:
- Different output modes, from a count of differences to full row dumps.
- Low bandwidth mode available, reducing the number of round-trips so only actual differences go through the network.
- A progress bar with estimated remaining amount of work.
- Server load is targeted toward only the “right” database server.
The sync tool is used to synchronize data in corresponding tables of a left and right pair of databases. Key features of the sync tool are:
- All features of the Compare tool also apply to syncs
- Automatically orders table syncs to avoid foreign key conflicts.
- You can configure the Sync policy to ignore deletes in left database, or to ignore creating records in right database, and other such combinations
- Provides two prebuilt conflict resolution methods, either left db wins or right db wins
- Custom conflict resolution methods specifiable via ruby code snippets
- Merge decisions can optionally be logged in the rubyrep event log table.
Of course RubyRep also provides a replication tool. Some of the key features of the replication tool include:
- Automatically sets up all necessary triggers, log tables, etc.
- Automatically discovers newly added tables and synchronizes the table content
- Automatically reconfigures sequences to avoid duplicate key conflicts
- Tracks changes to primary key columns
- Can implement either master-slave or master-master replication
- Prebuilt conflict resolution methods available include left or right wins, or earlier, later change wins
- Custom conflict resolution specifiable via ruby code snippets
- Replication decisions can optionally be logged in the rubyrep event log table
One of the problems common to replication solutions is that of setting up new nodes. With Slony, there are always some headaches caused by high load on master database server, as a result of the TRUNCATE/COPY cycle Slony goes through. In the case of RubyRep, most of the CPU load is on the slave server, and you can use the Sync command in advance before you start replicating database. RubyRep also provides some flexibility to ignore the Sync commands if you don’t want to sync the database again.
For installation refer to http://www.rubyrep.org/installation.html
# rubyrep --help Usage: /usr/local/bin/rubyrep [general options] command [parameters, ...] Asynchronous master-master replication of relational databases. Available options: --verbose Show errors with full stack trace -v, --version Show version information. --help Show this message Available commands: generate Generates a configuration file template help Shows detailed help for the specified command proxy Proxies connections from rubyrep commands to the database replicate Starts a replication process scan Scans for differing records between databases sync Syncs records between databases uninstall Removes all rubyrep tables, triggers, etc. from "left" and "right" database
rubyrep generate myrubyrep.conf
Checkout http://www.rubyrep.org/tutorial.html for scanning & sync & replication configs