Multi-instance-precommit (MIP) has been recently presented as an innovative transaction management scheme in support of reliability for Atomic Transactions in multitier (e.g. Web-based) systems. With this scheme, fail-over of a previously activated transaction can be supported via simple retry logics, which do not require knowledge about whether, and on which sites, the original transaction was precommitted. Mutual deadlock between the original and the retried transaction are prevented via MIP facilities, which also support reconciliation mechanisms for at-most-once transaction execution semantic. In this article we present an extension of the open source PostgreSQL database system in order to support MIP. The extension is based on the exploitation of PostgreSQL native multiversion concurrency control scheme. We also present an experimental evaluation based on the TPC-W benchmark, aimed at quantifying the relative overhead of MIP facilities on transaction execution latency, system throughput and storage usage.