Moving on

Today was my last day at 2ndQuadrant.

The experience of working with 2ndQuadrant in the last couple of years has been very positive. I just decided it was time for a change. Being able to work on interesting problems during my time at 2ndQuadrant, both as a Postgres developer and as a consultant has been great fun, and very personally rewarding. I would like to acknowledge the invaluable support of both Simon Riggs and Greg Smith - thank you both. I wish the entire 2ndQuadrant staff all the best.

I expect to remain active as a Postgres developer, and already have plans to relocate to work for another company that is well known within the community.

Finding plans in pg_stat_plans easily with pg_find_plans

As I recently blogged about, pg_stat_plans is a PostgreSQL satellite project I've been working on that aims to support earlier versions of Postgres that cannot use the new pg_stat_statements, and to track execution costs at the plan rather than the query granularity. It allows the user to easily explain each stored query text to see the plan for the entry, and has features that facilitate monitoring planner regressions.

Since PostgreSQL 9.0, support for machine-readable EXPLAIN output has existed. I'm not aware that anyone else got around to actually doing something interesting with this capability, though. I knew that in order to get the most benefit from pg_stat_plans, it ought to be possible to leverage this capability to search for plans based on arbitrary criteria, directly from SQL.

I've written an experimental submodule of pg_stat_plans, called pg_find_plans, that is designed to do just that - to quickly find plans and their execution costs, for those plans that, say, perform a sequential scan on a known large table.

Notes on index-only scans

One of the most important performance features in Postgres 9.2 is index-only scans: the ability for certain types of queries to be performed without retrieving data from tables, potentially greatly reducing the amount of I/O needed. I recently completely overhauled the Index-only scans PostgreSQL wiki page, so that the page is now targeted at experienced PostgreSQL users that hope to get the most out of the feature.

My apologies to the authors of the feature, Robert Haas, Ibrar Ahmed, Heikki Linnakangas and Tom Lane, if my handling of the topic seems to focus on the negatives. Any reasonable article about any given index-only scan implementation would have to extensively discuss that implementation's limitations. Any discussion of Postgres index-only scans that focussed on the positives would be much shorter, and would essentially just say: "Index-only scans can make some of your queries go much faster!".

First release of pg_stat_plans

Anyone who attended my recent talk at Postgres Open, which was co-presented with my 2ndQuadrant colleague Greg Smith, "Beyond Query Logging", will be aware that pg_stat_statements, the standard contrib module that assigns execution costs to queries and makes them available from a view in the database, has been improved considerably in the recent 9.2 Postgres release. It has been improved in a way that we believe will alter the preferred approach to workload analysis on PostgreSQL databases away from log analysis tools, which just don't offer the performance, flexibility or granularity of this new approach.

We also announced a new open source tool that addresses a related but slightly different problem (the analysis of plan execution costs, and planner regressions), as well as making most of the benefits of pg_stat_statements on 9.2 available to users stuck on earlier versions of Postgres. This new tool is called pg_stat_plans, and is itself based on pg_stat_statements.