Re: [Chicken-users] status of chickenlib: build process and mysqlinterface usage sample

[Tony Garnock-Jones]

Ed Watkeys wrote:
> Tony Garnock-Jones said:
> > I'm curious - what about the interface makes it too slow?
>
> I can only speak in general, but interfaces that return an entire result
> set consume lots of memory and can introduce lots of latency. For large
> result sets, the ability to get a row at a time allows for low-latency,
> constant-space programs.

The main workhorse of Oleg's interface is DB:for-each (which is more of 
a kind of map, really), which applies a procedure to each row in the 
result set sequentially. The code uses result-sets internally in the 
chickenlib implementation; of course, Oleg's reference implementation 
using pipes and an interactive query tool don't work quite the same :-)

An example use:

   ...

   (let ((db (DB:mysql-connect #f mysql-user mysql-pass "mysql")))
     (let ((column-names (map string->symbol
                              (DB:fetch-column db "describe host"))))
       (cout "Columns: " #\newline)
       (writen column-names)
       (cout "Values: " #\newline)
       (DB:for-each (lambda vals (writen (map list column-names vals)))
                    db
                    "select * from host"))
     (DB:close db))

   ...

This looks at some of the metadata present in a mysql database, first by 
grabbing an entire column as a Scheme list using the convenience 
function DB:fetch-column, and then a row at a time using DB:for-each.

Tony