The PostgreSQL Global Development Group has released an important update with fixes for multiple security issues to all supported versions of the PostgreSQL database system, which includes minor versions 9.4.1, 9.3.6, 9.2.10, 9.1.15, and 9.0.19. This update includes both security fixes and fixes for issues discovered since the last release. In particular for the 9.4 update, there is a change to the way unicode strings are escaped for the JSON and JSONB data types.
All users should update their PostgreSQL installation at the next opportunity.

The PostgreSQL memory at first sight looks simple. If compared with the complex structures implemented in the other DBMS to a careless reader could seem rudimentary. However, the memory and in particular the shared buffers implementation is complex and sophisticated. This chapter will dig down deep into the PostgreSQL’s memory.

3.1 The shared buffer

The shared buffer is a segment allocated at cluster’s startup. Its size is determined by the GUC parameter shared_buffers and the size can be changed only restarting the cluster. The shared buffer is used to manage the data pages as seen in 2.6, which are called buffers when loaded in rhw memory. Having a RAM segment is not uncommon in the database universe. Is a rapid exchange area where the buffers are kept across the sessions and keeps the data near the CPU. Like his competitors PostgreSQL strives to keep in memory what is important things and not everything. In the era of the in memory databases this could seems an obsolete concept. Unfortunately the truth is that the resources, and so the money, are not infinite. Before digging into the technical details we’ll have a look to the history of the memory manager. The way PostgreSQL sticks an elephant into a small car without Timelord technology.

2.4 The background writer

Before the spread checkpoints the only solution to ease down the IO spike caused by the checkpoint was to tweak the background writer. This process were introduced with the revolutionary PostgreSQL 8.0. The writer, as the name suggests, works in the background searching for dirty buffers to write on the data files. The writer works in rounds. When the process awakes scans the shared buffer for dirty buffers. When the amount of buffers cleaned reaches the value set in bgwriter_lru_maxpages the process sleeps for the time set in bgwriter_delay.

The cluster in action

PostgreSQL delivers his services ensuring the ACID rules are enforced at any time. This chapter will give an outlook of a ``day in the life’' of a PostgreSQL’s cluster. The chapter approach is purposely generic. At this stage is very important to understand the global picture rather the technical details.

After the startup

When the cluster completes the startup procedure it starts accepting the connections. When a connection is successful then the postgres main process forks into a new backend process which is assigned to the connection for the connection’s lifetime. The fork is quite expensive and does not work very well for a high rate of connection’s requests. The maximum number of connections is set at startup and cannot be changed dynamically. Whether the connection is used or not for each connection slot are consumed 400 bytes of shared memory.
Alongside the client’s request the cluster have several subprocesses working in the background.

The acronym RTFM stands for Read The Fucking Manual. It’s quite obvious that reading the manual is the perfect approach for finding the correct information or at least a hint for finding the solution.

The false confidence or a lack of humbleness make people to forget how important is to read the documents. Understanding the documents is the next step, and is not simple indeed. In particular if the background is poor or the reader have preconceptions which alter the word meanings.