diff options
Diffstat (limited to 'Documentation/technical/reftable.txt')
| -rw-r--r-- | Documentation/technical/reftable.txt | 49 |
1 files changed, 32 insertions, 17 deletions
diff --git a/Documentation/technical/reftable.txt b/Documentation/technical/reftable.txt index 2951840e9c..d7c3b645cf 100644 --- a/Documentation/technical/reftable.txt +++ b/Documentation/technical/reftable.txt @@ -446,7 +446,7 @@ especially if readers will not use the object name to ref mapping. Object blocks use unique, abbreviated 2-32 object name keys, mapping to ref blocks containing references pointing to that object directly, or as the peeled value of an annotated tag. Like ref blocks, object blocks use -the file's standard block size. The abbrevation length is available in +the file's standard block size. The abbreviation length is available in the footer as `obj_id_len`. To save space in small files, object blocks may be omitted if the ref @@ -872,17 +872,11 @@ A repository must set its `$GIT_DIR/config` to configure reftable: Layout ^^^^^^ -A collection of reftable files are stored in the `$GIT_DIR/reftable/` -directory: - -.... -00000001-00000001.log -00000002-00000002.ref -00000003-00000003.ref -.... - -where reftable files are named by a unique name such as produced by the -function `${min_update_index}-${max_update_index}.ref`. +A collection of reftable files are stored in the `$GIT_DIR/reftable/` directory. +Their names should have a random element, such that each filename is globally +unique; this helps avoid spurious failures on Windows, where open files cannot +be removed or overwritten. It suggested to use +`${min_update_index}-${max_update_index}-${random}.ref` as a naming convention. Log-only files use the `.log` extension, while ref-only and mixed ref and log files use `.ref`. extension. @@ -893,9 +887,9 @@ 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 `$GIT_DIR/reftable/tables.list` to determine which @@ -940,7 +934,7 @@ new reftable and atomically appending it to the stack: 3. Select `update_index` to be most recent file's `max_update_index + 1`. 4. Prepare temp reftable `tmp_XXXXXX`, including log entries. -5. Rename `tmp_XXXXXX` to `${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 +987,7 @@ 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 +999,27 @@ 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 should proceed as follows: + +* take a lock `tables.list.lock` to prevent concurrent modifications +* refresh the reftable stack, by reading `tables.list` +* for each `*.ref` file, remove it if +** it is not mentioned in `tables.list`, and +** its max update_index is not beyond the max update_index of the stack + + Alternatives considered ~~~~~~~~~~~~~~~~~~~~~~~ |