Re: Against sqlite3!!!

[Qiantan Hong <qhong@mit.edu>]

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> Please don't:
> - The function is called `load` (`load-file` is just one of the
>  *commands* defined to access the functionality interactively).
> - This is a security hole.
> 
> `insert-file-contents + read` should hopefully still be fast enough.
Indeed, I’ve attached an updated version, it runs as fast.
I also added kv-rem

> Actually, Emacs can serialize/deserialize hash table directly via
> prin1-to-string & read

ik, this is the current standard practice.
If you follow the sqlite3 thread you see the problem is saving/loading
(aka printing/reading) whole hash table/alist takes too much time.

The point of my implementation is to do it incrementally everytime
the key value store is mutated.



[-- Attachment #2: resist!.el --]
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;;; resist!.el --- Against SQLite3!  -*- lexical-binding: t; -*-

(cl-defstruct (kv-store (:constructor make-kv-store-1)) path table)
(defun make-kv-store (path)
  (let* ((kv-store (make-kv-store-1 :path path))
         (kv-store-table (make-hash-table :test 'equal))
         need-compactification)
    (when (file-exists-p path)
      (condition-case nil
          (with-temp-buffer
            (insert-file-contents path)
            (while (< (point) (1- (point-max))) ; exclude trailing newline
              (let ((entry (read (current-buffer))))
                (pcase (car entry)
                  ('++ (puthash (cadr entry) (caddr entry) kv-store-table))
                  ('-- (remhash (cadr entry) kv-store-table))))))
        (end-of-file
         ;; We might encounter trailing unbalanced form if Emacs
         ;; crashed in the middle of `kv-put'.  We compact the file
         ;; and fix unbalanced form as a side effect
         (setq need-compactification t)))
      (setf (kv-store-table kv-store) kv-store-table))
    (when need-compactification
      (compact-kv-store kv-store))
    kv-store))
(defsubst kv-put-log (key value)
  (let ((print-length nil) (print-level nil))
    (prin1 (list '++ key value) (current-buffer)))
  (insert "\n"))
(defsubst kv-rem-log (key)
  (let ((print-length nil) (print-level nil))
    (prin1 (list '-- key) (current-buffer)))
  (insert "\n"))
(defun compact-kv-store (kv-store)
  ;; dump the full content of kv-store-table at once
  ;; to compress the log
  (with-temp-buffer
    (maphash (lambda (key value) (kv-put-log key value))
             (kv-store-table kv-store))
    (let ((file-precious-flag t))
      (write-file (kv-store-path kv-store)))))
(defun kv-put (key value kv-store)
  (with-temp-buffer
    (kv-put-log key value)
    (append-to-file nil nil (kv-store-path kv-store)))
  (puthash key value (kv-store-table kv-store)))
(defun kv-rem (key)
  (with-temp-buffer
    (kv-rem-log key)
    (append-to-file nil nil (kv-store-path kv-store)))
  (remhash key (kv-store-table kv-store)))
(defun kv-get (key kv-store)
  (gethash key (kv-store-table kv-store)))
(provide 'resist!)