1. Is pgmemcache application transparent ?
2. Is there any synchronization between memcached and PostgreSQL Shared buffers ?
pgmemcache(memcached) is not application transparent, you need to do changes in the application for pushing or retreiving the data from the cache.
EnterpriseDB, product PostgresPlus Advance Server includes a feature called Infinite Cache, which is based on production proven technology memcached the open source distributed object cache.
About EnterpriseDB, the Enterprise PostgreSQL Company, provides enterprise-class PostgreSQL products of the world’s most advanced open source database. The company’s Postgres Plus products are ideally suited for transaction-intensive applications requiring superior performance, massive scalability and compatibility with proprietary database products.
Above diagram helps to understand the architecture of pgmemcache vs infinite cache. In infinite cache, all the pages are first searched in shared_buffers and then in Infinite Cache. Synchronization between shared buffer cache and infinite cache makes application transparency, which is not the case with pgmemcache.
Infinite Cache, is faster and completely application transparent. No special code is needed from developers. Warms up your cache with multiple parallel processes and pre-loads cache at startup reducing warming time.
To avail infinite cache you have to download the PostgresPlus Advance Server which is Oracle Compatible product bundled with Infinite Cache.
Implementation of Infinite cache is as simple as memcached, below link will help in setting up the infinite cache.
Very informative discussion on PostgreSQL Community Forum:-