Goal ~~~~ We want to make it possible to use the split-index feature automatically by just setting a new "core.splitIndex" configuration variable to true. This can be valuable as split-index can help significantly speed up `git rebase` especially along with the work to libify `git apply` that has been merged to master (see https://github.com/git/git/commit/81358dc238372793b1590efa149cc1581d1fbd98) and is now in v2.11. Design ~~~~~~ The design is similar as the previous work that introduced "core.untrackedCache". The new "core.splitIndex" configuration option can be either true, false or undefined which is the default. When it is true, the split index is created, if it does not already exists, when the index is read. When it is false, the split index is removed if it exists, when the index is read. Otherwise it is left as is. Along with this new configuration variable, the two following options are also introduced: - splitIndex.maxPercentChange This is to avoid having too many changes accumulating in the split index while in split index mode. The git-update-index documentation says: If split-index mode is already enabled and `--split-index` is given again, all changes in $GIT_DIR/index are pushed back to the shared index file. but it is probably better to not expect the user to think about it and to have a mechanism that pushes back all changes to the shared index file automatically when some threshold is reached. The default threshold is when the number of entries in the split index file reaches 20% of the number of entries in the shared index file. The new "splitIndex.maxPercentChange" config option lets people tweak this value. - splitIndex.sharedIndexExpire To make sure that old sharedindex files are eventually removed when a new one has been created, we "touch" the shared index file every time a split index file using the shared index file is either created or read from. Then we can delete shared indexes with an mtime older than one week (by default), when we create a new shared index file. The new "splitIndex.sharedIndexExpire" config option lets people tweak this grace period. This idea was suggested by Duy in: https://public-inbox.org/git/CACsJy8BqMFASHf5kJgUh+bd7XG98CafNydE964VJyPXz-emEvA@xxxxxxxxxxxxxx/ and after some experiments, I agree that it is much simpler than what I thought could be done during our discussion. Junio also thinks that we have to do "time-based GC" in: https://public-inbox.org/git/xmqqeg33ccjj.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxx/ Note that this patch series doesn't address a leak when removing a split-index, but Duy wrote that he has a patch to fix this leak: https://public-inbox.org/git/CACsJy8AisF2ZVs7JdnVFp5wdskkbVQQQ=DBq5UzE1MOsCfBMtQ@xxxxxxxxxxxxxx/ Highlevel view of the patches in the series ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Except for patch 1/22 and 1/22, there are 3 big steps, one for each new configuration variable introduced. There only small differences between this patch series and the v3 patch series sent a few months ago. - Patch 1/22 marks a message for translation. It is not new and can be applied separately. - Patch 2/22 improves the existing indentation style of t1700 by using different here document style. It is a new preparatory patch suggested by Junio. Step 1 is: - Patches 3/22 to 6/22 introduce the functions that are reading the "core.splitIndex" configuration variable and tweaking the split index depending on its value. - Patch 7/22 adds a few tests for the new feature. - Patches 8/22 and 9/22 add some documentation for the new feature. There is no change since v3 in this step. Step 2 is: - Patches 10/22 and 11/22 introduce the functions that are reading the "splitIndex.maxPercentChange" configuration variable and regenerating a new shared index file depending on its value. Patch 11/12 has a few changes suggested by Junio since v3, see https://public-inbox.org/git/CAP8UFD3_1EN=0EsD12Cew1MuW8yhtPAZw0M_g3wmvKFk-uGXxw@xxxxxxxxxxxxxx/ - Patch 12/22 adds a few tests for the new feature. - Patch 13/22 add some documentation for the new feature. The added documentation has been reworded a little bit since v3 as suggested by Junio. Step 3 is: - Patches 14/22 to 17/22 introduce the functions that are reading the "splitIndex.sharedIndexExpire" configuration variable and expiring old shared index files depending on its value. Patch 15/22 has a few changes suggested by Ramsay and Junio in http://public-inbox.org/git/a1a44640-ff6c-2294-72ac-46322eff8505@xxxxxxxxxxxxxxxxxxxx/ http://public-inbox.org/git/xmqqbmunq6mg.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxx/ The main change is that the new freshen_shared_index() will now warn if the split-index file has been written but the shared index file could't be freshened. Another change is that in 17/22 the new "splitIndex.sharedIndexExpire" config variable now defaults to "2.weeks.ago" instead of "one.week.ago" in v3. - Patch 18/22 adds a few tests for the new feature. It is changed a bit to account for the change in 17/22. Also some flakyness in one of the tests has been fixed by using a 5 second, instead of 1 second, delay, thanks to Ramsay and Peff, see http://public-inbox.org/git/818851a6-c3ef-618e-4146-518fbe6bd837@xxxxxxxxxxxxxxxxxxxx/ - Patches 19/22 and 20/22 were new patches in v3. They update the mtime of the shared index file when a split index based on the shared index file is read from. 19/22 is a refactoring to make the actual change in 20/22 easier. Patch 20/22 has been changed a little bit since v3 to take into account changes in 17/22. - Patches 21/22 and 22/22 add some documentation for the new feature. Patch 21/22 has been changed to avoid using "mtime" as suggested by Junio. Links ~~~~~ This patch series is also available here: https://github.com/chriscool/git/commits/config-split-index The previous versions were: RFC: https://github.com/chriscool/git/commits/config-split-index7 v1: https://github.com/chriscool/git/commits/config-split-index72 v2: https://github.com/chriscool/git/commits/config-split-index99 v3: https://github.com/chriscool/git/commits/config-split-index102 On the mailing list the related patch series and discussions were: RFC: https://public-inbox.org/git/20160711172254.13439-1-chriscool@xxxxxxxxxxxxx/ v1: https://public-inbox.org/git/20161023092648.12086-1-chriscool@xxxxxxxxxxxxx/ v2: https://public-inbox.org/git/20161217145547.11748-1-chriscool@xxxxxxxxxxxxx/ v3: https://public-inbox.org/git/20161226102222.17150-1-chriscool@xxxxxxxxxxxxx/ Christian Couder (22): config: mark an error message up for translation t1700: change here document style config: add git_config_get_split_index() split-index: add {add,remove}_split_index() functions read-cache: add and then use tweak_split_index() update-index: warn in case of split-index incoherency t1700: add tests for core.splitIndex Documentation/config: add information for core.splitIndex Documentation/git-update-index: talk about core.splitIndex config var config: add git_config_get_max_percent_split_change() read-cache: regenerate shared index if necessary t1700: add tests for splitIndex.maxPercentChange Documentation/config: add splitIndex.maxPercentChange sha1_file: make check_and_freshen_file() non static read-cache: touch shared index files when used config: add git_config_get_expiry() from gc.c read-cache: unlink old sharedindex files t1700: test shared index file expiration read-cache: refactor read_index_from() read-cache: use freshen_shared_index() in read_index_from() Documentation/config: add splitIndex.sharedIndexExpire Documentation/git-update-index: explain splitIndex.* Documentation/config.txt | 29 ++++ Documentation/git-update-index.txt | 43 ++++- builtin/gc.c | 15 +- builtin/update-index.c | 25 +-- cache.h | 8 + config.c | 42 ++++- read-cache.c | 157 ++++++++++++++++-- sha1_file.c | 2 +- split-index.c | 22 +++ split-index.h | 2 + t/t1700-split-index.sh | 324 +++++++++++++++++++++++++++---------- 11 files changed, 539 insertions(+), 130 deletions(-) -- 2.12.0.22.g0672473d40
