motiejus
/
jgit
1
Fork 0
Code Releases Activity

Documentation/technical/reftable: change suggested file names 

By using ${min_update}-${max_update} as file name template, we
guarantee that each file has a unique name.
This allows data from open files to be cached across reloads of the
stack.

This is in anticipation of Change I1837f268e 
("file: implement FileReftableDatabase"), which is the first
implementation of reftable on a filesystem.

Change-Id: I7ef0610eb60c494165382d0c372afcf41f074393
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
This commit is contained in:
Han-Wen Nienhuys 2019-08-22 15:47:17 +02:00 committed by Matthias Sohn
parent b4e5ae3b34
commit cf11a03bc2
1 changed files with 15 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
Documentation/technical/reftable.md
View File

@ -775,12 +775,12 @@ directory. This prevents loose references from being stored.
A collection of reftable files are stored in the `$GIT_DIR/reftable/` A collection of reftable files are stored in the `$GIT_DIR/reftable/`
directory: directory:
00000001.log 00000001-00000001.log
00000001.ref 00000002-00000002.ref
00000002.ref 00000003-00000003.ref
where reftable files are named by a unique name such as produced by where reftable files are named by a unique name such as produced by
the function `${update_index}.ref`. the function `${min_update_index}-${max_update_index}.ref`.
Log-only files use the `.log` extension, while ref-only and mixed ref Log-only files use the `.log` extension, while ref-only and mixed ref
and log files use `.ref`. extension. and log files use `.ref`. extension.
@ -790,9 +790,9 @@ files, one per line, in order, from oldest (base) to newest (most
recent): recent):
$ cat .git/refs $ cat .git/refs
00000001.log 00000001-00000001.log
00000001.ref 00000002-00000002.ref
00000002.ref 00000003-00000003.ref
Readers must read `$GIT_DIR/refs` to determine which files are Readers must read `$GIT_DIR/refs` to determine which files are
relevant right now, and search through the stack in reverse order relevant right now, and search through the stack in reverse order
@ -819,8 +819,8 @@ new reftable and atomically appending it to the stack:
1. Acquire `refs.lock`. 1. Acquire `refs.lock`.
2. Read `refs` to determine current reftables. 2. Read `refs` to determine current reftables.
3. Select `update_index` to be most recent file's `max_update_index + 1`. 3. Select `update_index` to be most recent file's `max_update_index + 1`.
4. Prepare temp reftable `${update_index}_XXXXXX`, including log entries. 4. Prepare temp reftable `tmp_XXXXXX`, including log entries.
5. Rename `${update_index}_XXXXXX` to `${update_index}.ref`. 5. Rename `tmp_XXXXXX` to `${update_index}-${update_index}.ref`.
6. Copy `refs` to `refs.lock`, appending file from (5). 6. Copy `refs` to `refs.lock`, appending file from (5).
7. Rename `refs.lock` to `refs`. 7. Rename `refs.lock` to `refs`.
@ -865,12 +865,13 @@ is going to compact B and C, leaving A and D alone.
Ownership of these locks prevents other processes from trying Ownership of these locks prevents other processes from trying
to compact these files. to compact these files.
3. Release `refs.lock`. 3. Release `refs.lock`.
4. Compact `B` and `C` into a temp file `${min_update_index}_XXXXXX`. 4. Compact `B` and `C` into a temp file `${min_update_index}-${max_update_index}_XXXXXX`.
5. Reacquire lock `refs.lock`. 5. Reacquire lock `refs.lock`.
6. Verify that `B` and `C` are still in the stack, in that order. This 6. Verify that `B` and `C` are still in the stack, in that order. This
should always be the case, assuming that other processes are adhering should always be the case, assuming that other processes are adhering
to the locking protocol. to the locking protocol.
7. Rename `${min_update_index}_XXXXXX` to `${min_update_index}_2.ref`. 7. Rename `${min_update_index}-${max_update_index}_XXXXXX` to
`${min_update_index}-${max_update_index}.ref`.
8. Write the new stack to `refs.lock`, replacing `B` and `C` with the 8. Write the new stack to `refs.lock`, replacing `B` and `C` with the
file from (4). file from (4).
9. Rename `refs.lock` to `refs`. 9. Rename `refs.lock` to `refs`.
@ -879,6 +880,9 @@ is going to compact B and C, leaving A and D alone.
This strategy permits compactions to proceed independently of updates. 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.
## Alternatives considered ## Alternatives considered
### bzip packed-refs ### bzip packed-refs