dir: force untracked cache with core.untrackedCache
PATCH 1/1 dir: force untracked cache with core.untrackedCache
From: Derrick Stolee <[email protected]>
The GIT_FORCE_UNTRACKED_CACHE environment variable writes the untracked cache more frequently than the core.untrackedCache config variable. This is due to how read_directory() handles the creation of an untracked cache. The old mechanism required using something like 'git update-index --untracked-cache' before the index would actually contain an untracked cache. This was noted as a performance problem on macOS in the past, and this is a resolution for that issue.
The decision to not write the untracked cache without an environment variable tracks back to fc9ecbeb9 (dir.c: don't flag the index as dirty for changes to the untracked cache, 2018-02-05). The motivation of that change is that writing the index is expensive, and if the untracked cache is the only thing that needs to be written, then it is more expensive than the benefit of the cache. However, this also means that the untracked cache never gets populated, so the user who enabled it via config does not actually get the extension until running 'git update-index --untracked-cache' manually or using the environment variable.
We have had a version of this change in the microsoft/git fork for a few major releases now. It has been working well to get users into a good state. Yes, that first index write is slow, but the remaining index writes are much faster than they would be without this change.
---
dir: force untracked cache with core.untrackedCache
We have seen users in the wild that have had core.untrackedCache enabled, but never actually have an untracked cache created for them. We have a test in t7063 that shows git status should write the untracked cache, so I'm not exactly sure how users are in this state for long.
This patch fixes the situation. I also know of another group that sets GIT_FORCE_UNTRACKED_CACHE=1 in their developer environment in order to get this behavior.
-Stolee
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1058%2Fderrickstolee%2Funtracked-cache-write-more-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1058/derrickstolee/untracked-cache-write-more-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1058
dir.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
dir.c +3 -1
@@ -2936,7 +2936,9 @@ int read_directory(struct dir_struct *dir, struct index_state *istate,if (force_untracked_cache <0 ) force_untracked_cache = -git_env_bool ("GIT_FORCE_UNTRACKED_CACHE" ,0 ); +git_env_bool ("GIT_FORCE_UNTRACKED_CACHE" ,-1 ); +if (force_untracked_cache <0 ) + force_untracked_cache = (istate->repo->settings.core_untracked_cache ==UNTRACKED_CACHE_WRITE ); if (force_untracked_cache && dir->untracked == istate->untracked && (dir->untracked->dir_opened ||
base-commit: b80121027d1247a0754b3cc46897fee75c050b44
Signature · 1 line
gitgitgadget
Quoted 9 lines · Derrick Stolee via GitGitGadget
From: Derrick Stolee <[email protected]>
The
GIT_FORCE_UNTRACKED_CACHEenvironment variable writes the untracked cache more frequently than the core.untrackedCache config variable. This is due to howread_directory()handles the creation of an untracked cache. The old mechanism required using something like 'git update-index --untracked-cache' before the index would actually contain an untracked cache. This was noted as a performance problem on macOS in the past, and this is a resolution for that issue.
"The old mechanism" meaning "core.untrackedCache does not add a new one; it only updates an existing one"? What "this" refers to that was noted as a problem on macOS is not quite clear; is "writing untracked cache is a performance problem"? And the last "this" which is a resolution is "not to add untrackedCache merely because the configuration variable says we are allowed to use it"?
Quoted 10 lines
The decision to not write the untracked cache without an environment variable tracks back to
fc9ecbeb9(dir.c: don't flag the index as dirty for changes to the untracked cache, 2018-02-05). The motivation of that change is that writing the index is expensive, and if the untracked cache is the only thing that needs to be written, then it is more expensive than the benefit of the cache. However, this also means that the untracked cache never gets populated, so the user who enabled it via config does not actually get the extension until running 'git update-index --untracked-cache' manually or using the environment variable.
OK. It was invented solely as a test mechanism it seems, but at least to the workflow of Microsoft folks, once we spent cycles to prepare UNTR data, it helps their future use of the index to spend a bit more cycle to write it out, instead of discarding.
I have to wonder if there are workflows that are sufficiently different from what Microsoft folks use that the write-out cost of more frequent updates to the untracked cache outweigh the runtime performance boost of not having to run around and readdir() for untracked files?
ad0fb659 (repo-settings: parse core.untrackedCache, 2019-08-13) explains that unset core.untrackedCache means "keep", and "true" means untracked cache is "automatically added", which this change is not invalidated, so I guess there is no need to update anything in the documentation for this change. In fact, we might be able to sell this change as a bugfix (i.e. "I set the configuration to 'true' but it wasn't written out when it should have").
Quoted 17 lines
dir.c +3
-1@@ -2936,7 +2936,9 @@ int read_directory(struct dir_struct *dir, struct index_state *istate,if (force_untracked_cache <0 ) force_untracked_cache = -git_env_bool ("GIT_FORCE_UNTRACKED_CACHE" ,0 ); +git_env_bool ("GIT_FORCE_UNTRACKED_CACHE" ,-1 ); +if (force_untracked_cache <0 ) + force_untracked_cache = (istate->repo->settings.core_untracked_cache ==UNTRACKED_CACHE_WRITE ); if (force_untracked_cache && dir->untracked == istate->untracked && (dir->untracked->dir_opened ||base-commit:
b80121027d1247a0754b3cc46897fee75c050b44
Quoted 12 lines · Junio C Hamano
Quoted 9 lines · Derrick Stolee via GitGitGadget
From: Derrick Stolee <[email protected]>
The
GIT_FORCE_UNTRACKED_CACHEenvironment variable writes the untracked cache more frequently than the core.untrackedCache config variable. This is due to howread_directory()handles the creation of an untracked cache. The old mechanism required using something like 'git update-index --untracked-cache' before the index would actually contain an untracked cache. This was noted as a performance problem on macOS in the past, and this is a resolution for that issue.
Quoted 6 lines
"The old mechanism" meaning "core.untrackedCache does not add a new one; it only updates an existing one"? What "this" refers to that was noted as a problem on macOS is not quite clear; is "writing untracked cache is a performance problem"? And the last "this" which is a resolution is "not to add untrackedCache merely because the configuration variable says we are allowed to use it"?
Right. I can see how that is confusing. Here's another attempt:
The GIT_FORCE_UNTRACKED_CACHE environment variable writes the untracked cache more frequently than the core.untrackedCache config variable. This is due to how read_directory() handles the creation of an untracked cache.
Before this change, Git would not create the untracked cache extension for an index that did not already have one. Users would need to run a command such as 'git update-index --untracked-cache' before the index would actually contain an untracked cache.
In particular, users noticed that the untracked cache would not appear even with core.untrackedCache=true. Some users reported setting GIT_FORCE_UNTRACKED_CACHE=1 in their engineering system environment to ensure the untracked cache would be created.
Quoted 16 lines
Quoted 10 lines
The decision to not write the untracked cache without an environment variable tracks back to
fc9ecbeb9(dir.c: don't flag the index as dirty for changes to the untracked cache, 2018-02-05). The motivation of that change is that writing the index is expensive, and if the untracked cache is the only thing that needs to be written, then it is more expensive than the benefit of the cache. However, this also means that the untracked cache never gets populated, so the user who enabled it via config does not actually get the extension until running 'git update-index --untracked-cache' manually or using the environment variable.OK. It was invented solely as a test mechanism it seems, but at least to the workflow of Microsoft folks, once we spent cycles to prepare UNTR data, it helps their future use of the index to spend a bit more cycle to write it out, instead of discarding.
Quoted 5 lines
I have to wonder if there are workflows that are sufficiently different from what Microsoft folks use that the write-out cost of more frequent updates to the untracked cache outweigh the runtime performance boost of not having to run around and
readdir()for untracked files?
I think the only difference here is the transition state from no cache to an existing cache. From then on, the cache is kept up-to-date with the same frequency as without this change.
Quoted 7 lines
ad0fb659(repo-settings: parse core.untrackedCache, 2019-08-13) explains that unset core.untrackedCache means "keep", and "true" means untracked cache is "automatically added", which this change is not invalidated, so I guess there is no need to update anything in the documentation for this change. In fact, we might be able to sell this change as a bugfix (i.e. "I set the configuration to 'true' but it wasn't written out when it should have").
Yes, I believe this to be the case. Hopefully the rewritten paragraphs above make this more clear.
Thanks,
-Stolee
PATCH v2 1/1 dir: force untracked cache with core.untrackedCache
In reply to Derrick Stolee via GitGitGadgetFrom: Derrick Stolee <[email protected]>
The GIT_FORCE_UNTRACKED_CACHE environment variable writes the untracked cache more frequently than the core.untrackedCache config variable. This is due to how read_directory() handles the creation of an untracked cache.
Before this change, Git would not create the untracked cache extension for an index that did not already have one. Users would need to run a command such as 'git update-index --untracked-cache' before the index would actually contain an untracked cache.
In particular, users noticed that the untracked cache would not appear even with core.untrackedCache=true. Some users reported setting GIT_FORCE_UNTRACKED_CACHE=1 in their engineering system environment to ensure the untracked cache would be created.
The decision to not write the untracked cache without an environment variable tracks back to fc9ecbeb9 (dir.c: don't flag the index as dirty for changes to the untracked cache, 2018-02-05). The motivation of that change is that writing the index is expensive, and if the untracked cache is the only thing that needs to be written, then it is more expensive than the benefit of the cache. However, this also means that the untracked cache never gets populated, so the user who enabled it via config does not actually get the extension until running 'git update-index --untracked-cache' manually or using the environment variable.
We have had a version of this change in the microsoft/git fork for a few major releases now. It has been working well to get users into a good state. Yes, that first index write is slow, but the remaining index writes are much faster than they would be without this change.
---
dir: force untracked cache with core.untrackedCache
We have seen users in the wild that have had core.untrackedCache enabled, but never actually have an untracked cache created for them. We have a test in t7063 that shows git status should write the untracked cache, so I'm not exactly sure how users are in this state for long.
This patch fixes the situation. I also know of another group that sets GIT_FORCE_UNTRACKED_CACHE=1 in their developer environment in order to get this behavior.
-Stolee
Update in v2
============
* Edited the commit message to be clearer.
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1058%2Fderrickstolee%2Funtracked-cache-write-more-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1058/derrickstolee/untracked-cache-write-more-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1058
Range-diff vs v1:
1: 061ee9a379d ! 1: 8d132bc5566 dir: force untracked cache with core.untrackedCache
@@ Commit message
The GIT_FORCE_UNTRACKED_CACHE environment variable writes the untracked cache more frequently than the core.untrackedCache config variable. This is due to how read_directory() handles the creation of an untracked
- cache. The old mechanism required using something like 'git update-index
- --untracked-cache' before the index would actually contain an untracked
- cache. This was noted as a performance problem on macOS in the past, and
- this is a resolution for that issue.
+ cache.
+
+ Before this change, Git would not create the untracked cache extension
+ for an index that did not already have one. Users would need to run a
+ command such as 'git update-index --untracked-cache' before the index
+ would actually contain an untracked cache.
+
+ In particular, users noticed that the untracked cache would not appear
+ even with core.untrackedCache=true. Some users reported setting
+ GIT_FORCE_UNTRACKED_CACHE=1 in their engineering system environment to
+ ensure the untracked cache would be created.
The decision to not write the untracked cache without an environment variable tracks back to fc9ecbeb9 (dir.c: don't flag the index as dirty
dir.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
dir.c +3 -1
@@ -2936,7 +2936,9 @@ int read_directory(struct dir_struct *dir, struct index_state *istate,if (force_untracked_cache <0 ) force_untracked_cache = -git_env_bool ("GIT_FORCE_UNTRACKED_CACHE" ,0 ); +git_env_bool ("GIT_FORCE_UNTRACKED_CACHE" ,-1 ); +if (force_untracked_cache <0 ) + force_untracked_cache = (istate->repo->settings.core_untracked_cache ==UNTRACKED_CACHE_WRITE ); if (force_untracked_cache && dir->untracked == istate->untracked && (dir->untracked->dir_opened ||
base-commit: b80121027d1247a0754b3cc46897fee75c050b44
Signature · 1 line
gitgitgadget
Quoted 28 lines · Derrick Stolee via GitGitGadget
From: Derrick Stolee <[email protected]>
The
GIT_FORCE_UNTRACKED_CACHEenvironment variable writes the untracked cache more frequently than the core.untrackedCache config variable. This is due to howread_directory()handles the creation of an untracked cache.Before this change, Git would not create the untracked cache extension for an index that did not already have one. Users would need to run a command such as 'git update-index --untracked-cache' before the index would actually contain an untracked cache.
In particular, users noticed that the untracked cache would not appear even with core.untrackedCache=true. Some users reported setting GIT_FORCE_UNTRACKED_CACHE=1 in their engineering system environment to ensure the untracked cache would be created.
The decision to not write the untracked cache without an environment variable tracks back to
fc9ecbeb9(dir.c: don't flag the index as dirty for changes to the untracked cache, 2018-02-05). The motivation of that change is that writing the index is expensive, and if the untracked cache is the only thing that needs to be written, then it is more expensive than the benefit of the cache. However, this also means that the untracked cache never gets populated, so the user who enabled it via config does not actually get the extension until running 'git update-index --untracked-cache' manually or using the environment variable.
Quoted 7 lines
We have had a version of this change in the microsoft/git fork for a few major releases now. It has been working well to get users into a good state. Yes, that first index write is slow, but the remaining index writes are much faster than they would be without this change.
Signed-off-by Derrick Stolee <[email protected]>---
Will queue.
Thanks.