Re: [PATCH] doc/reftable: document how to handle windows

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 26, 2021, 05:49 UTC
Message-ID: <xmqq35yo459k.fsf@gitster.c.googlers.com>
In-Reply-To: <pull.951.git.git.1611589125365.gitgitgadget@gmail.com>

"Han-Wen Nienhuys via GitGitGadget" <gitgitgadget@gmail.com> writes:

Show 16 quoted lines

>  $ cat .git/reftable/tables.list
> -00000001-00000001.log
> -00000002-00000002.ref
> -00000003-00000003.ref
> +00000001-00000001-RANDOM1.log
> +00000002-00000002-RANDOM2.ref
> +00000003-00000003-RANDOM3.ref
>  ....
> @@ -940,7 +944,7 @@ new reftable and atomically appending it to the stack:
>  3.  Select `update_index` to be most recent file's
>  `max_update_index + 1`.
>  4.  Prepare temp reftable `tmp_XXXXXX`, including log entries.
> -5.  Rename `tmp_XXXXXX` to `${update_index}-${update_index}.ref`.
> +5.  Rename `tmp_XXXXXX` to `${update_index}-${update_index}-${random}.ref`.
>  6.  Copy `tables.list` to `tables.list.lock`, appending file from (5).
>  7.  Rename `tables.list.lock` to `tables.list`.

Is this because we have been assuming that in step 5. we can "overwrite" (i.e. take over the name, implicitly unlinking the existing one) the existing 0000001-00000001.ref with the newly prepared one, which is not doable on Windows?

We must prepare for two "randoms" colliding and retrying the renaming step anyway, so would it make more sense to instead use a non-random suffix (i.e. try "-0.ref" first, and when it fails, readdir for 0000001-00000001-*.ref to find the latest suffix and increment it)?

Show 8 quoted lines

> @@ -993,7 +997,7 @@ prevents other processes from trying to compact these files.
>  should always be the case, assuming that other processes are adhering to
>  the locking protocol.
>  7.  Rename `${min_update_index}-${max_update_index}_XXXXXX` to
> -`${min_update_index}-${max_update_index}.ref`.
> +`${min_update_index}-${max_update_index}-${random}.ref`.
>  8.  Write the new stack to `tables.list.lock`, replacing `B` and `C`
>  with the file from (4).

Likewise.