Firstly, I should thank my company for giving me an opportunity to work mostly with PostgreSQL HA stuff. I have worked with very good clients who has implemented Clustering with PostgreSQL. So, my article here is to give little idea on how HA clustering will work with PostgreSQL.
PostgreSQL has built-in functionality for High Availability like Warm Standby,Hot Standby and Streaming Replication. But, missing few features like Switchover/Switchback, failover automation, minimal downtime etc.
Word “Replication” means a process of sharing information so as to ensure consistency between redundant resources, such as software or hardware components, to improve reliability, fault-tolerance, or accessibility.
Replication is very interesting subject in any databases. In database competition world, PostgreSQL has its own uniqueness in RDBMS Open source for High availability. Latest PostgreSQL 9.1 has in-built support of Synchronous and Asynchronous replication. In-built Asynchronous replications are Warm Standby, Hot Standby and Streaming Replication and with third party tools Slony,Londiste,Mammoth etc.
In PostgreSQL, database creation time is not stored in any of the pg_catalogs. So question arises, how do we know when was database created.
For every database, a directory is created with database-oid number under $PGDATA/base along with a set of OID’s,OID_fsm,OID_vm, PG_VERSION files for each Object(Tables/Indexes/View/ etc.,).
Every OID,OID_fsm,OID_vm, files will be get updated as per the changes made at database-level. However, PG_VERSION file will never get updated on any changes made to the database.
Connection pooling, Why we go for connection pooling in PostgreSQL, When your application demands for very good number of concurrent connection hits then you need to approach it, because Connection pool sits between your application and the database.
Idea behind connection pool is that you have enough connections to use of all the available resources and any incoming requests are re-used without dropping the database connection and keeping ready for a new connection to use.
In my recent post on pgmemcache, there were couple of questions asked which were really interesting and made me to work on it. I should thank for it :)
Questions:
Is pgmemcache application transparent ? Is there any synchronization between memcached and PostgreSQL Shared buffers ? Answer:
pgmemcache(memcached) is not application transparent, you need to do changes in the application for pushing or retreiving the data from the cache.