From: Han-Wen Nienhuys <hanwen@xxxxxxxxxx>
On Windows we can't delete or overwrite files opened by other processes. Here we
sketch how to handle this situation.
Signed-off-by: Han-Wen Nienhuys <hanwen@xxxxxxxxxx>
---
doc/reftable: document how to handle windows
On Windows we can't delete or overwrite files opened by other processes.
Here we sketch how to handle this situation.
Signed-off-by: Han-Wen Nienhuys hanwen@xxxxxxxxxx
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-951%2Fhanwen%2Fwindows-doc-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-951/hanwen/windows-doc-v1
Pull-Request: https://github.com/git/git/pull/951
Documentation/technical/reftable.txt | 38 +++++++++++++++++++++-------
1 file changed, 29 insertions(+), 9 deletions(-)
diff --git a/Documentation/technical/reftable.txt b/Documentation/technical/reftable.txt
index 8095ab2590c..d8be27d88c1 100644
--- a/Documentation/technical/reftable.txt
+++ b/Documentation/technical/reftable.txt
@@ -876,13 +876,13 @@ A collection of reftable files are stored in the `$GIT_DIR/reftable/`
directory:
....
-00000001-00000001.log
-00000002-00000002.ref
-00000003-00000003.ref
+00000001-00000001-RANDOM1.log
+00000002-00000002-RANDOM2.ref
+00000003-00000003-RANDOM3.ref
....
where reftable files are named by a unique name such as produced by the
-function `${min_update_index}-${max_update_index}.ref`.
+function `${min_update_index}-${max_update_index}-${random}.ref`.
Log-only files use the `.log` extension, while ref-only and mixed ref
and log files use `.ref`. extension.
@@ -893,9 +893,9 @@ current files, one per line, in order, from oldest (base) to newest
....
$ 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
....
Readers must read `$GIT_DIR/reftable/tables.list` to determine which
@@ -906,6 +906,10 @@ Reftable files not listed in `tables.list` may be new (and about to be
added to the stack by the active writer), or ancient and ready to be
pruned.
+The random suffix added to table filenames ensures that we never attempt to
+overwrite an existing table, which is necessary for this scheme to work on
+Windows
+
Backward compatibility
^^^^^^^^^^^^^^^^^^^^^^
@@ -940,7 +944,7 @@ new reftable and atomically appending it to the stack:
3. Select `update_index` to be most recent file's
`max_update_index + 1`.
4. Prepare temp reftable `tmp_XXXXXX`, including log entries.
-5. Rename `tmp_XXXXXX` to `${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`.
@@ -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).
9. Rename `tables.list.lock` to `tables.list`.
@@ -1005,6 +1009,22 @@ This strategy permits compactions to proceed independently of updates.
Each reftable (compacted or not) is uniquely identified by its name, so
open reftables can be cached by their name.
+Windows
+^^^^^^^
+
+On windows, and other systems that do not allow deleting or renaming to open
+files, compaction may succeed, but other readers may prevent obsolete tables
+from being deleted.
+
+On these platforms, the following strategy can be followed: on closing a
+reftable stack, reload `tables.list`, and delete any tables no longer mentioned
+in `tables.list`.
+
+Irregular program exit may still leave about unused files. In this case, a
+cleanup operation can read `tables.list`, note its modification timestamp, and
+delete any unreferenced `*.ref` files that are older.
+
+
Alternatives considered
~~~~~~~~~~~~~~~~~~~~~~~
base-commit: 66e871b6647ffea61a77a0f82c7ef3415f1ee79c
--
gitgitgadget
