diff --git a/js-assembler/db-cache.rkt b/js-assembler/db-cache.rkt
index af132e2..acb6c04 100644
--- a/js-assembler/db-cache.rkt
+++ b/js-assembler/db-cache.rkt
@@ -3,7 +3,8 @@
 (require (planet ryanc/db)
          (prefix-in whalesong: "../version.rkt")
          racket/file
-         racket/path)
+         racket/path
+         file/md5)
 
 (define cache-directory-path
   (build-path (find-system-path 'pref-dir)
@@ -16,7 +17,28 @@
   (unless (directory-exists? cache-directory-path)
     (make-directory* cache-directory-path)))
   
-(create-cache-directory!)
+
+(define (ensure-cache-db-structure!)
+  (when (not (file-exists? whalesong-cache.sqlite3))
+    ;; Clear existing cache files: they're obsolete.
+    (for ([file (directory-list cache-directory-path)])
+      (when (file-exists? (build-path cache-directory-path file))
+        (with-handlers ([exn:fail? void])
+          (delete-file (build-path cache-directory-path file)))))
+    
+    (define conn 
+      (sqlite3-connect #:database whalesong-cache.sqlite3
+                       #:mode 'create))
+    (query-exec conn
+                (string-append
+                 "create table cache(path string not null primary key, "
+                 " md5sum string not null, "
+                 "data blob not null);"))
+    (query-exec conn
+                "CREATE INDEX cache_md5sum_idx ON cache (md5sum);")
+    (disconnect conn)))
+
+
 
 (define whalesong-cache.sqlite3 
   (build-path cache-directory-path 
@@ -24,24 +46,43 @@
                       whalesong:version)))
 
 
-(when (not (file-exists? whalesong-cache.sqlite3))
-  (define conn 
-     (sqlite3-connect #:database whalesong-cache.sqlite3
-		      #:mode 'create))
-  (query-exec conn
-              (string-append
-               "create table cache(path string not null primary key, "
-               " md5sum string not null, "
-               "data blob not null);"))
-  (disconnect conn))
- 
+(create-cache-directory!)
+(ensure-cache-db-structure!)
 
 (define conn 
   (sqlite3-connect #:database whalesong-cache.sqlite3))
 
 
-(define (cached? path)
-  #f)
+(define lookup-cache-stmt 
+  (prepare conn (string-append "select path, md5sum, data "
+                               "from cache "
+                               "where path=? and md5sum=?")))
+(define insert-cache-stmt 
+  (prepare conn (string-append "insert into cache(path, md5sum, data)"
+                               " values (?, ?, ?);")))
 
-(define (save-in-cache! path)
-  (void))
\ No newline at end of file
+;; cached?:
+(define (cached? path)
+  (cond
+    [(file-exists? path)
+     (query-maybe-row conn 
+                      lookup-cache-stmt 
+                      (path->string path)
+                      (call-with-input-file* path md5))]
+    [else
+     #f]))
+
+
+
+;; save-in-cache!: path string -> void
+;; Saves a record.
+(define (save-in-cache! path data)
+  (cond
+    [(file-exists? path)
+     (query-exec conn 
+                 insert-cache-stmt
+                 (path->string path)
+                 (call-with-input-file* path md5)
+                 data)]
+    [else
+     (error 'save-in-cache! "File ~e does not exist" path)]))
\ No newline at end of file