Le 9 juil. 2014 20:36, "David G Johnston" <david.g.johns...@gmail.com> a écrit : > > csrajmohan wrote > > "EXPLAIN (format XML) " command in PostgreSQL9.3.4 gives the plan chosen > > by > > the optimizer in XML format. In my program, I have to extract certain data > > about optimizer plan from this XML output. I am using *LibXML2* library > > for > > parsing the XML. I had successfully extracted information about which > > relations are involved and what joins are used by parsing the XML. But > > I am *unable > > to extract the* *order of joining the relations from the XML output*. I > > conceptually understood that the reverse level order traversal of binary > > tree representation of the XML plan will give correct ordering of joins > > applied. But I could not figure out how do I get that from the XML? Does > > libXML2 support anything of this sort? If not how should I proceed to > > tackle this? > > So, since nothing better has been forthcoming in your other two posts on > this topic I'll just say that likely you will have much better luck using > SAX-based processing as opposed to DOM-based processing. I seriously doubt > native/core PostgreSQL facilities will allow you to do what you desire. > > As you said, hierarchy and physical output order determines the "order of > joining" within the planner so you have to capture and track such relational > information during your processing - which is made much easier if you simply > traverse the output node-by-node exactly as a SAX based parser does. > > Though pgAdminIII has a visual query display that you might look at for > inspiration. >
FWIW, pgadmin's visual explain doesn't (yet?) use XML or json or yaml output.
