Against sqlite3!!! (Was: sqlite3)

[Qiantan Hong <qhong@mit.edu>]

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I’ve attached a pure Emacs Lisp implementation of persistent key value store.

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;;; resist!.el --- Against SQLite3!  -*- lexical-binding: t; -*-

(defvar kv-store-table)
(defmacro --kv (key value)
  (puthash key value kv-store-table)
  nil)
(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 c
          (load-file path)
        (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 kv-store)
  (let ((print-length nil) (print-level nil))
    (prin1 `(--kv ,key ,value) (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))
             (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 kv-store)
    (append-to-file nil nil (kv-store-path kv-store)))
  (puthash key value (kv-store-table kv-store)))
(defun kv-get (key kv-store)
  (gethash key (kv-store-table kv-store)))
(provide 'resist!)

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