Rewriting db-fetch-query-results

After [d39d60ec68a2f5c2909b891ca949cb5ca39d39f5] I realized that the array was being dereferenced every row of the results.
This patch creates a set of closures for reading the columns, and then maps across those closures on each row.

On SBCL 1.0.25:
a query that returns ~2k rows, repeated 50 times is about 3% faster, same memory
a query that returns 1 row repeated 2000 times is about the same speed, 10% GREATER memory

Going to revert this patch, but wanted to have it recorded.

diff --git a/db-odbc/odbc-dbi.lisp b/db-odbc/odbc-dbi.lisp
index 58ef2d729a78d24bb086e6a065d1726de9b7338c..07bfedf28c5c117900993fc51de92c53fd74cdcc 100644 (file)
--- a/db-odbc/odbc-dbi.lisp
+++ b/db-odbc/odbc-dbi.lisp
@@ -309,30 +309,38 @@ the query against." ))
     (with-slots (column-count column-data-ptrs column-c-types column-sql-types
                  column-out-len-ptrs column-precisions hstmt computed-result-types)
         query
-      (let* ((rows-fetched 0)
-             (rows
-              (loop for i from 0
-                  until (or (and count (= i count))
-                            (= (%sql-fetch hstmt) odbc::$SQL_NO_DATA_FOUND))
-                  collect
-                    (loop for result-type across computed-result-types
-                        for data-ptr across column-data-ptrs
-                        for c-type across column-c-types
-                        for sql-type across column-sql-types
-                        for out-len-ptr across column-out-len-ptrs
-                        for precision across column-precisions
-                        for j from 0    ; column count is zero based in lisp
-                        collect
-                          (progn
-                            (incf rows-fetched)
-                            (cond ((< 0 precision (query-width query))
-                                   (read-data data-ptr c-type sql-type out-len-ptr result-type))
-                                  ((zerop (get-cast-long out-len-ptr))
-                              nil)
-                                  (t
-                                   (read-data-in-chunks hstmt j data-ptr c-type sql-type
-                                                        out-len-ptr result-type))))))))
-        (values rows query rows-fetched)))))
+      (labels
+         ((create-column-fetcher (result-type data-ptr c-type sql-type out-len-ptr precision column-nr)
+            (lambda ()
+              (cond ((< 0 precision (query-width query))
+                     (read-data data-ptr c-type sql-type out-len-ptr result-type))
+                    ((zerop (get-cast-long out-len-ptr))
+                     nil)
+                    (t
+                     (read-data-in-chunks hstmt column-nr data-ptr c-type sql-type
+                                          out-len-ptr result-type))))))
+       (let ((fetchers (make-array column-count :fill-pointer 0 :element-type 'function)))
+         ;;; Map across the columns, creating a set of fetch functions
+         (loop for result-type across computed-result-types
+               for data-ptr across column-data-ptrs
+               for c-type across column-c-types
+               for sql-type across column-sql-types
+               for out-len-ptr across column-out-len-ptrs
+               for precision across column-precisions
+               for column-nr from 0 ; column count is zero based in lisp
+               do
+            (vector-push (create-column-fetcher result-type data-ptr c-type sql-type
+                                out-len-ptr precision column-nr)
+                   fetchers))
+         ;; keep fetching rows until we meet the count parameter,
+         ;; or the %sql-fetch says we're done.
+         (loop for i from 0
+               until (or (and count (= i count))
+                         (= (%sql-fetch hstmt) odbc::$SQL_NO_DATA_FOUND))
+               ;;collect the results of the fetch functions to make a row.
+               collect (map 'list #'funcall fetchers) into rows
+               finally (return (values rows query i))
+               ))))))
 
 (defun db-query (database query-expression &key result-types width)
   (let ((free-query (get-free-query database)))