On December 24, 2016 9:52 PM Craig Ringer [mailto:craig.ringer@2ndquadrant.com] wrote:
> Personally I can see such an option being ok as an initdb-time setting or at CREATE DATABASE time. Case folding can know the current db from global context.
>
> It'd have to be fast though. Very fast.
That seems reasonable. In fact, it is nicer to configure at the database level, rather than at the cluster level. I did not know it was possible to tell the database from global context. Since a connection only allows access to a single database, it makes sense that could be possible.
A check of a single global configuration variable to switch between one of three handler paths would be very small compared with the character-by-character checks currently performed by downcase_identifier(), though, of course, the extra check would not be free.
However, it would likely be faster to setup up the processing to call through a global pointer to one of three handler functions. On most Intel processors, at least, that extra pointer indirection costs little to nothing. The pointer could be set up during database connect (I do not know what I am talking about here, but there must be such a process somewhere).
Presumably, the handler pointer would have to go into the global database descriptor whatever that is. Or, if you allow use of global objects for storing information about database scope run-time configuration, it could just be a function pointer stored with the handlers. The database initialization processing could call a setup function when it runs to select the correct handling for its configuration. The default would be the current downcase_identifier() handling.
Does this seem like an approach that would meet your "Very fast" requirement?