Tag: graph

Waiting for PostgreSQL 14 – SEARCH and CYCLE clauses

On 1st of February 2021, Peter Eisentraut committed patch:

SEARCH and CYCLE clauses 
 
This adds the SQL standard feature that adds the SEARCH and CYCLE
clauses to recursive queries to be able to do produce breadth- or
depth-first search orders and detect cycles.  These clauses can be
rewritten into queries using existing syntax, and that is what this
patch does in the rewriter.
 
Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/db80ceee-6f97-9b4a-8ee8-3ba0c58e5be2@2ndquadrant.com

Continue reading Waiting for PostgreSQL 14 – SEARCH and CYCLE clauses

What is the overhead of logging?

update at the end of the post!

There obviously is one – after all, logging information has to be more expensive than not logging it. But how big is it? And more importantly, what is the difference between logging to stderr/file, csvlog and syslog? And what about syslog to remote machine?

Let's see.

Continue reading What is the overhead of logging?

How to get shortest connection between two cities

Yesterday, on #postgresql on irc some guy asked:

22:28 < rafasc> i am trying to use plpgsql to find the shortest path between two cities, each pair of cities has one or more edges, each edge has a different wheight.
22:28 < rafasc> Is there a easy way to compute the shortest path between two cities?

Well, I was not really in a mood to solve it, so I just told him to try with recursive queries, and went on my way.

But I thought about it. And decided to see if I can write the query.

Continue reading How to get shortest connection between two cities