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[bug#41658] [PATCH] fixes / improvements for (guix store database)
From: |
Danny Milosavljevic |
Subject: |
[bug#41658] [PATCH] fixes / improvements for (guix store database) |
Date: |
Thu, 4 Jun 2020 19:00:40 +0200 |
Hi Ludo,
Hi Caleb,
On Thu, 04 Jun 2020 18:40:35 +0200
Ludovic Courtès <ludo@gnu.org> wrote:
> Nice. It would be great if you could report it upstream (Danny and/or
> myself can then patch it directly in guile-sqlite3 and push out a
> release) and refer to the issue from here.
I agree. It's easy to change sqlite-finalize in guile-sqlite3 to
call sqlite-reset, basically just adapt
(define sqlite-finalize
(let ((f (pointer->procedure
int
(dynamic-func "sqlite3_finalize" libsqlite3)
(list '*))))
(lambda (stmt)
;; Note: When STMT is cached, this is a no-op. This ensures caching
;; actually works while still separating concerns: users can turn
;; caching on and off without having to change the rest of their code.
(when (and (stmt-live? stmt)
(not (stmt-cached? stmt)))
(let ((p (stmt-pointer stmt)))
(sqlite-remove-statement! (stmt->db stmt) stmt)
(set-stmt-live?! stmt #f)
(f p))))))
so that it calls sqlite-reset in the "when"'s new "else" branch there.
(we could also always call sqlite3_reset on sqlite-finalize anyway, it wouldn't
hurt but it wouldn't help either)
I agree that sqlite-finalize should model sqlite's finalization behavior as
much as possible.
Also, the comment about this being a no-op is not true then anymore.
We should definitely also pick up Caleb's comment upstream:
+ ;; Cached statements aren't reset when sqlite-finalize is invoked on
+ ;; them. This can cause problems with automatically-started transactions:
+ ;;
+ ;; "An implicit transaction (a transaction that is started automatically,
+ ;; not a transaction started by BEGIN) is committed automatically when the
+ ;; last active statement finishes. A statement finishes when its last cursor
+ ;; closes, which is guaranteed to happen when the prepared statement is
+ ;; reset or finalized. Some statements might "finish" for the purpose of
+ ;; transaction control prior to being reset or finalized, but there is no
+ ;; guarantee of this."
+ ;;
+ ;; Thus, it's possible for an implicitly-started transaction to hang around
+ ;; until sqlite-reset is called when the cached statement is next
+ ;; used. Because the transaction is committed automatically only when the
+ ;; *last active statement* finishes, the implicitly-started transaction may
+ ;; later be upgraded to a write transaction (!) and this non-reset statement
+ ;; will still be keeping the transaction from committing until it is next
+ ;; used or the database connection is closed. This has the potential to make
+ ;; (exclusive) write access to the database necessary for much longer than
+ ;; it should be.
+ ;;
+ ;; (see https://www.sqlite.org/lang_transaction.html)
@Caleb:
Could you file an issue at
https://notabug.org/guile-sqlite3/guile-sqlite3/issues
and pull request so this is auditable?
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