- 31 12月, 2013 3 次提交
-
-
由 Vicent Marti 提交于
This commit extends more the functionality of `pack-objects` by allowing it to write out a `.bitmap` index next to any written packs, together with the `.idx` index that currently gets written. If bitmap writing is enabled for a given repository (either by calling `pack-objects` with the `--write-bitmap-index` flag or by having `pack.writebitmaps` set to `true` in the config) and pack-objects is writing a packfile that would normally be indexed (i.e. not piping to stdout), we will attempt to write the corresponding bitmap index for the packfile. Bitmap index writing happens after the packfile and its index has been successfully written to disk (`finish_tmp_packfile`). The process is performed in several steps: 1. `bitmap_writer_set_checksum`: this call stores the partial checksum for the packfile being written; the checksum will be written in the resulting bitmap index to verify its integrity 2. `bitmap_writer_build_type_index`: this call uses the array of `struct object_entry` that has just been sorted when writing out the actual packfile index to disk to generate 4 type-index bitmaps (one for each object type). These bitmaps have their nth bit set if the given object is of the bitmap's type. E.g. the nth bit of the Commits bitmap will be 1 if the nth object in the packfile index is a commit. This is a very cheap operation because the bitmap writing code has access to the metadata stored in the `struct object_entry` array, and hence the real type for each object in the packfile. 3. `bitmap_writer_reuse_bitmaps`: if there exists an existing bitmap index for one of the packfiles we're trying to repack, this call will efficiently rebuild the existing bitmaps so they can be reused on the new index. All the existing bitmaps will be stored in a `reuse` hash table, and the commit selection phase will prioritize these when selecting, as they can be written directly to the new index without having to perform a revision walk to fill the bitmap. This can greatly speed up the repack of a repository that already has bitmaps. 4. `bitmap_writer_select_commits`: if bitmap writing is enabled for a given `pack-objects` run, the sequence of commits generated during the Counting Objects phase will be stored in an array. We then use that array to build up the list of selected commits. Writing a bitmap in the index for each object in the repository would be cost-prohibitive, so we use a simple heuristic to pick the commits that will be indexed with bitmaps. The current heuristics are a simplified version of JGit's original implementation. We select a higher density of commits depending on their age: the 100 most recent commits are always selected, after that we pick 1 commit of each 100, and the gap increases as the commits grow older. On top of that, we make sure that every single branch that has not been merged (all the tips that would be required from a clone) gets their own bitmap, and when selecting commits between a gap, we tend to prioritize the commit with the most parents. Do note that there is no right/wrong way to perform commit selection; different selection algorithms will result in different commits being selected, but there's no such thing as "missing a commit". The bitmap walker algorithm implemented in `prepare_bitmap_walk` is able to adapt to missing bitmaps by performing manual walks that complete the bitmap: the ideal selection algorithm, however, would select the commits that are more likely to be used as roots for a walk in the future (e.g. the tips of each branch, and so on) to ensure a bitmap for them is always available. 5. `bitmap_writer_build`: this is the computationally expensive part of bitmap generation. Based on the list of commits that were selected in the previous step, we perform several incremental walks to generate the bitmap for each commit. The walks begin from the oldest commit, and are built up incrementally for each branch. E.g. consider this dag where A, B, C, D, E, F are the selected commits, and a, b, c, e are a chunk of simplified history that will not receive bitmaps. A---a---B--b--C--c--D \ E--e--F We start by building the bitmap for A, using A as the root for a revision walk and marking all the objects that are reachable until the walk is over. Once this bitmap is stored, we reuse the bitmap walker to perform the walk for B, assuming that once we reach A again, the walk will be terminated because A has already been SEEN on the previous walk. This process is repeated for C, and D, but when we try to generate the bitmaps for E, we can reuse neither the current walk nor the bitmap we have generated so far. What we do now is resetting both the walk and clearing the bitmap, and performing the walk from scratch using E as the origin. This new walk, however, does not need to be completed. Once we hit B, we can lookup the bitmap we have already stored for that commit and OR it with the existing bitmap we've composed so far, allowing us to limit the walk early. After all the bitmaps have been generated, another iteration through the list of commits is performed to find the best XOR offsets for compression before writing them to disk. Because of the incremental nature of these bitmaps, XORing one of them with its predecesor results in a minimal "bitmap delta" most of the time. We can write this delta to the on-disk bitmap index, and then re-compose the original bitmaps by XORing them again when loaded. This is a phase very similar to pack-object's `find_delta` (using bitmaps instead of objects, of course), except the heuristics have been greatly simplified: we only check the 10 bitmaps before any given one to find best compressing one. This gives good results in practice, because there is locality in the ordering of the objects (and therefore bitmaps) in the packfile. 6. `bitmap_writer_finish`: the last step in the process is serializing to disk all the bitmap data that has been generated in the two previous steps. The bitmap is written to a tmp file and then moved atomically to its final destination, using the same process as `pack-write.c:write_idx_file`. Signed-off-by: NVicent Marti <tanoku@gmail.com> Signed-off-by: NJeff King <peff@peff.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Vicent Marti 提交于
In this patch, we use the bitmap API to perform the `Counting Objects` phase in pack-objects, rather than a traditional walk through the object graph. For a reasonably-packed large repo, the time to fetch and clone is often dominated by the full-object revision walk during the Counting Objects phase. Using bitmaps can reduce the CPU time required on the server (and therefore start sending the actual pack data with less delay). For bitmaps to be used, the following must be true: 1. We must be packing to stdout (as a normal `pack-objects` from `upload-pack` would do). 2. There must be a .bitmap index containing at least one of the "have" objects that the client is asking for. 3. Bitmaps must be enabled (they are enabled by default, but can be disabled by setting `pack.usebitmaps` to false, or by using `--no-use-bitmap-index` on the command-line). If any of these is not true, we fall back to doing a normal walk of the object graph. Here are some sample timings from a full pack of `torvalds/linux` (i.e. something very similar to what would be generated for a clone of the repository) that show the speedup produced by various methods: [existing graph traversal] $ time git pack-objects --all --stdout --no-use-bitmap-index \ </dev/null >/dev/null Counting objects: 3237103, done. Compressing objects: 100% (508752/508752), done. Total 3237103 (delta 2699584), reused 3237103 (delta 2699584) real 0m44.111s user 0m42.396s sys 0m3.544s [bitmaps only, without partial pack reuse; note that pack reuse is automatic, so timing this required a patch to disable it] $ time git pack-objects --all --stdout </dev/null >/dev/null Counting objects: 3237103, done. Compressing objects: 100% (508752/508752), done. Total 3237103 (delta 2699584), reused 3237103 (delta 2699584) real 0m5.413s user 0m5.604s sys 0m1.804s [bitmaps with pack reuse (what you get with this patch)] $ time git pack-objects --all --stdout </dev/null >/dev/null Reusing existing pack: 3237103, done. Total 3237103 (delta 0), reused 0 (delta 0) real 0m1.636s user 0m1.460s sys 0m0.172s Signed-off-by: NVicent Marti <tanoku@gmail.com> Signed-off-by: NJeff King <peff@peff.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Jeff King 提交于
This function actually does three things: 1. Check whether we've already added the object to our packing list. 2. Check whether the object meets our criteria for adding. 3. Actually add the object to our packing list. It's a little hard to see these three phases, because they happen linearly in the rather long function. Instead, this patch breaks them up into three separate helper functions. The result is a little easier to follow, though it unfortunately suffers from some optimization interdependencies between the stages (e.g., during step 3 we use the packing list index from step 1 and the packfile information from step 2). More importantly, though, the various parts can be composed differently, as they will be in the next patch. Signed-off-by: NJeff King <peff@peff.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 25 10月, 2013 2 次提交
-
-
由 Vicent Marti 提交于
As the pack-objects system grows beyond the single pack-objects.c file, more parts (like the soon-to-exist bitmap code) will need to compute hashes for matching deltas. Factor out name_hash to make it available to other files. Signed-off-by: NVicent Marti <tanoku@gmail.com> Signed-off-by: NJeff King <peff@peff.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Vicent Marti 提交于
The hash table that stores the packing list for a given `pack-objects` run was tightly coupled to the pack-objects code. In this commit, we refactor the hash table and the underlying storage array into a `packing_data` struct. The functionality for accessing and adding entries to the packing list is hence accessible from other parts of Git besides the `pack-objects` builtin. This refactoring is a requirement for further patches in this series that will require accessing the commit packing list from outside of `pack-objects`. The hash table implementation has been minimally altered: we now use table sizes which are always a power of two, to ensure a uniform index distribution in the array. Signed-off-by: NVicent Marti <tanoku@gmail.com> Signed-off-by: NJeff King <peff@peff.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 29 8月, 2013 1 次提交
-
-
由 Nguyễn Thái Ngọc Duy 提交于
mark_edges_uninteresting() is always called with this form mark_edges_uninteresting(revs->commits, revs, ...); Remove the first argument and let mark_edges_uninteresting figure that out by itself. It helps answer the question "are this commit list and revs related in any way?" when looking at mark_edges_uninteresting implementation. Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 03 8月, 2013 1 次提交
-
-
由 Brandon Casey 提交于
Now that close_one_pack() has been introduced to handle file descriptor pressure, it is not strictly necessary to close the pack file descriptor in unuse_one_window() when we're under memory pressure. Jeff King provided a justification for leaving the pack file open: If you close packfile descriptors, you can run into racy situations where somebody else is repacking and deleting packs, and they go away while you are trying to access them. If you keep a descriptor open, you're fine; they last to the end of the process. If you don't, then they disappear from under you. For normal object access, this isn't that big a deal; we just rescan the packs and retry. But if you are packing yourself (e.g., because you are a pack-objects started by upload-pack for a clone or fetch), it's much harder to recover (and we print some warnings). Let's do so (or uh, not do so). Signed-off-by: NBrandon Casey <drafnel@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 05 2月, 2013 1 次提交
-
-
由 Junio C Hamano 提交于
Turn some boolean fields into bitfields and use uint32_t for name hash. This shrinks the size of the structure from 128 bytes to 120 bytes. Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 05 10月, 2012 1 次提交
-
-
由 Jeff King 提交于
The idea of the peel_ref function is to dereference tag objects recursively until we hit a non-tag, and return the sha1. Conceptually, it should return 0 if it is successful (and fill in the sha1), or -1 if there was nothing to peel. However, the current behavior is much more confusing. For a regular loose ref, the behavior is as described above. But there is an optimization to reuse the peeled-ref value for a ref that came from a packed-refs file. If we have such a ref, we return its peeled value, even if that peeled value is null (indicating that we know the ref definitely does _not_ peel). It might seem like such information is useful to the caller, who would then know not to bother loading and trying to peel the object. Except that they should not bother loading and trying to peel the object _anyway_, because that fallback is already handled by peel_ref. In other words, the whole point of calling this function is that it handles those details internally, and you either get a sha1, or you know that it is not peel-able. This patch catches the null sha1 case internally and converts it into a -1 return value (i.e., there is nothing to peel). This simplifies callers, which do not need to bother checking themselves. Two callers are worth noting: - in pack-objects, a comment indicates that there is a difference between non-peelable tags and unannotated tags. But that is not the case (before or after this patch). Whether you get a null sha1 has to do with internal details of how peel_ref operated. - in show-ref, if peel_ref returns a failure, the caller tries to decide whether to try peeling manually based on whether the REF_ISPACKED flag is set. But this doesn't make any sense. If the flag is set, that does not necessarily mean the ref came from a packed-refs file with the "peeled" extension. But it doesn't matter, because even if it didn't, there's no point in trying to peel it ourselves, as peel_ref would already have done so. In other words, the fallback peeling is guaranteed to fail. Signed-off-by: NJeff King <peff@peff.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 21 8月, 2012 1 次提交
-
-
由 Nguyễn Thái Ngọc Duy 提交于
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 10 7月, 2012 1 次提交
-
-
由 Junio C Hamano 提交于
The existing "cant_be_filename" that tells the function that the caller knows the arg is not a path (hence it does not have to be checked for absense of the file whose name matches it) is made into a bit in the flag word. Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 30 5月, 2012 1 次提交
-
-
由 Nguyễn Thái Ngọc Duy 提交于
git usually streams large blobs directly to packs. But there are cases where git can create large loose blobs (unpack-objects or hash-object over pipe). Or they can come from other git implementations. core.bigfilethreshold can also be lowered down and introduce a new wave of large loose blobs. Use streaming interface to read/compress/write these blobs in one go. Fall back to normal way if somehow streaming interface cannot be used. Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 19 5月, 2012 2 次提交
-
-
由 Nguyễn Thái Ngọc Duy 提交于
The function first decides if we want to copy data taken from existing pack verbatim or we want to encode the data ourselves for the packfile we are creating and then carries out the decision. Separate the latter phase into two helper functions, one for the case the data is reused, the other for the case the data is produced anew. A little twist is that it can later turn out that we cannot reuse the data after we initially decide to do so; in such a case, the "reuse" helper makes a call to "generate" helper. It is easier to follow than the current fallback code that uses "goto" inside a single large function. Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Nguyễn Thái Ngọc Duy 提交于
This is because all other places do "xx > big_file_threshold" Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 12 4月, 2012 1 次提交
-
-
由 Jeff King 提交于
When we pack everything into one big pack with "git repack -Ad", any unreferenced objects in to-be-deleted packs are exploded into loose objects, with the intent that they will be examined and possibly cleaned up by the next run of "git prune". Since the exploded objects will receive the mtime of the pack from which they come, if the source pack is old, those loose objects will end up pruned immediately. In that case, it is much more efficient to skip the exploding step entirely for these objects. This patch teaches pack-objects to receive the expiration information and avoid writing these objects out. It also teaches "git gc" to pass the value of gc.pruneexpire to repack (which in turn learns to pass it along to pack-objects) so that this optimization happens automatically during "git gc" and "git gc --auto". Signed-off-by: NJeff King <peff@peff.net> Acked-by: NNicolas Pitre <nico@fluxnic.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 27 2月, 2012 1 次提交
-
-
由 Michał Kiedrowicz 提交于
It looks like commit 99fb6e04 (pack-objects: convert to use parse_options(), 2012-02-01) moved the #ifdef NO_PTHREDS around but hasn't noticed that the 'arg' variable no longer is available. Signed-off-by: NMichał Kiedrowicz <michal.kiedrowicz@gmail.com> Acked-by: NNguyen Thai Ngoc Duy <pclouds@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 02 2月, 2012 3 次提交
-
-
由 Nguyễn Thái Ngọc Duy 提交于
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Nguyễn Thái Ngọc Duy 提交于
The comment was introduced in b5d97e6b (pack-objects: run rev-list equivalent internally. - 2006-09-04), stating that git pack-objects [options] base-name <refs...> is acceptable and refs should be passed into rev-list. But that's not true. All arguments after base-name are ignored. Remove the comment and reject this syntax (i.e. no more arguments after base name) Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Nguyễn Thái Ngọc Duy 提交于
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 13 1月, 2012 1 次提交
-
-
由 Jeff King 提交于
When creating a pack using objects that reside in existing packs, we try to avoid recomputing futile delta between an object (trg) and a candidate for its base object (src) if they are stored in the same packfile, and trg is not recorded as a delta already. This heuristics makes sense because it is likely that we tried to express trg as a delta based on src but it did not produce a good delta when we created the existing pack. As the pack heuristics prefer producing delta to remove data, and Linus's law dictates that the size of a file grows over time, we tend to record the newest version of the file as inflated, and older ones as delta against it. When creating a thin-pack to transfer recent history, it is likely that we will try to send an object that is recorded in full, as it is newer. But the heuristics to avoid recomputing futile delta effectively forbids us from attempting to express such an object as a delta based on another object. Sending an object in full is often more expensive than sending a suboptimal delta based on other objects, and it is even more so if we could use an object we know the receiving end already has (i.e. preferred base object) as the delta base. Tweak the recomputation avoidance logic, so that we do not punt on computing delta against a preferred base object. The effect of this change can be seen on two simulated upload-pack workloads. The first is based on 44 reflog entries from my git.git origin/master reflog, and represents the packs that kernel.org sent me git updates for the past month or two. The second workload represents much larger fetches, going from git's v1.0.0 tag to v1.1.0, then v1.1.0 to v1.2.0, and so on. The table below shows the average generated pack size and the average CPU time consumed for each dataset, both before and after the patch: dataset | reflog | tags --------------------------------- before | 53358 | 2750977 size after | 32398 | 2668479 change | -39% | -3% --------------------------------- before | 0.18 | 1.12 CPU after | 0.18 | 1.15 change | +0% | +3% This patch makes a much bigger difference for packs with a shorter slice of history (since its effect is seen at the boundaries of the pack) though it has some benefit even for larger packs. Signed-off-by: NJeff King <peff@peff.net> Acked-by: NNicolas Pitre <nico@fluxnic.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 02 12月, 2011 1 次提交
-
-
由 Junio C Hamano 提交于
This extends the earlier approach to stream a large file directly from the filesystem to its own packfile, and allows "git add" to send large files directly into a single pack. Older code used to spawn fast-import, but the new bulk-checkin API replaces it. Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 17 11月, 2011 1 次提交
-
-
由 Junio C Hamano 提交于
When --reuse-delta is in effect (which is the default), and an existing pack in the repository has the same object registered twice (e.g. one copy in a non-delta format and the other copy in a delta against some other object), an attempt to repack the repository can result in a cyclic delta dependency, causing write_one() function to infinitely recurse into itself. Detect such a case and break the loopy dependency by writing out an object that is involved in such a loop in the non-delta format. Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 29 10月, 2011 3 次提交
-
-
由 Junio C Hamano 提交于
Factor out a small logic out of the private write_pack_file() function in builtin/pack-objects.c. This changes the order of finishing multi-pack generation slightly. The code used to - adjust shared perm of temporary packfile - rename temporary packfile to the final name - update mtime of the packfile under the final name - adjust shared perm of temporary idxfile - rename temporary idxfile to the final name but because the helper does not want to do the mtime thing, the updated code does that step first and then all the rest. Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Junio C Hamano 提交于
Factor out a small logic out of the private write_pack_file() function in builtin/pack-objects.c Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Junio C Hamano 提交于
Factor out a small logic out of the private write_pack_file() function in builtin/pack-objects.c Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 28 10月, 2011 1 次提交
-
-
由 Nguyễn Thái Ngọc Duy 提交于
tree_entry_len() does not simply take two random arguments and return a tree length. The two pointers must point to a tree item structure, or struct name_entry. Passing random pointers will return incorrect value. Force callers to pass struct name_entry instead of two pointers (with hope that they don't manually construct struct name_entry themselves) Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 21 10月, 2011 1 次提交
-
-
由 Dan McGee 提交于
This brings back some of the performance lost in optimizing recency order inside pack objects. We were doing extreme amounts of object re-traversal: for the 2.14 million objects in the Linux kernel repository, we were calling add_to_write_order() over 1.03 billion times (a 0.2% hit rate, making 99.8% of of these calls extraneous). Two optimizations take place here- we can start our objects array iteration from a known point where we left off before we started trying to find our tags, and we don't need to do the deep dives required by add_family_to_write_order() if the object has already been marked as filled. These two optimizations bring some pretty spectacular results via `perf stat`: task-clock: 83373 ms --> 43800 ms (50% faster) cycles: 221,633,461,676 --> 116,307,209,986 (47% fewer) instructions: 149,299,179,939 --> 122,998,800,184 (18% fewer) Helped-by: Ramsay Jones (format string fix in "die" message) Signed-off-by: NDan McGee <dpmcgee@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 18 10月, 2011 3 次提交
-
-
由 Dan McGee 提交于
This removes the need to call this function recursively, shinking the code size slightly and netting a small performance increase. Signed-off-by: NDan McGee <dpmcgee@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Dan McGee 提交于
This is done in some of the new pack layout code introduced in commit 1b4bb16b. This more closely matches the nr_objects global that is unsigned that these variables are based off of and bounded by. Signed-off-by: NDan McGee <dpmcgee@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Dan McGee 提交于
This function is a whole 26 bytes when compiled on x86_64, but is currently invoked over 1.037 billion times when running pack-objects on the Linux kernel git repository. This is hitting the point where micro-optimizations do make a difference, and inlining it only increases the object file size by 38 bytes. As reported by perf, this dropped task-clock from 84183 to 83373 ms, and total cycles from 223.5 billion to 221.6 billion. Not astronomical, but worth getting for adding one word. Signed-off-by: NDan McGee <dpmcgee@gmail.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 15 10月, 2011 2 次提交
-
-
由 Jeff King 提交于
These can happen if another process simultaneously prunes a pack. But that is not usually an error condition, because a properly-running prune should have repacked the object into a new pack. So we will notice that the pack has disappeared unexpectedly, print a message, try other packs (possibly after re-scanning the list of packs), and find it in the new pack. Acked-by: NNicolas Pitre <nico@fluxnic.net> Signed-off-by: NJeff King <peff@peff.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Jeff King 提交于
It's possible that while pack-objects is running, a simultaneously running prune process might delete a pack that we are interested in. Because we load the pack indices early on, we know that the pack contains our item, but by the time we try to open and map it, it is gone. Since c715f783, we already protect against this in the normal object access code path, but pack-objects accesses the packs at a lower level. In the normal access path, we call find_pack_entry, which will call find_pack_entry_one on each pack index, which does the actual lookup. If it gets a hit, we will actually open and verify the validity of the matching packfile (using c715f783's is_pack_valid). If we can't open it, we'll issue a warning and pretend that we didn't find it, causing us to go on to the next pack (or on to loose objects). Furthermore, we will cache the descriptor to the opened packfile. Which means that later, when we actually try to access the object, we are likely to still have that packfile opened, and won't care if it has been unlinked from the filesystem. Notice the "likely" above. If there is another pack access in the interim, and we run out of descriptors, we could close the pack. And then a later attempt to access the closed pack could fail (we'll try to re-open it, of course, but it may have been deleted). In practice, this doesn't happen because we tend to look up items and then access them immediately. Pack-objects does not follow this code path. Instead, it accesses the packs at a much lower level, using find_pack_entry_one directly. This means we skip the is_pack_valid check, and may end up with the name of a packfile, but no open descriptor. We can add the same is_pack_valid check here. Unfortunately, the access patterns of pack-objects are not quite as nice for keeping lookup and object access together. We look up each object as we find out about it, and the only later when writing the packfile do we necessarily access it. Which means that the opened packfile may be closed in the interim. In practice, however, adding this check still has value, for three reasons. 1. If you have a reasonable number of packs and/or a reasonable file descriptor limit, you can keep all of your packs open simultaneously. If this is the case, then the race is impossible to trigger. 2. Even if you can't keep all packs open at once, you may end up keeping the deleted one open (i.e., you may get lucky). 3. The race window is shortened. You may notice early that the pack is gone, and not try to access it. Triggering the problem without this check means deleting the pack any time after we read the list of index files, but before we access the looked-up objects. Triggering it with this check means deleting the pack means deleting the pack after we do a lookup (and successfully access the packfile), but before we access the object. Which is a smaller window. Acked-by: NNicolas Pitre <nico@fluxnic.net> Signed-off-by: NJeff King <peff@peff.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 02 9月, 2011 1 次提交
-
-
由 Junio C Hamano 提交于
The traverse_commit_list() API takes two callback functions, one to show commit objects, and the other to show other kinds of objects. Even though the former has a callback data parameter, so that the callback does not have to rely on global state, the latter does not. Give the show_objects() callback the same callback data parameter. Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 05 8月, 2011 1 次提交
-
-
由 Michael Haggerty 提交于
Suggested by: Junio Hamano <gitster@pobox.com> Signed-off-by: NMichael Haggerty <mhagger@alum.mit.edu> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 09 7月, 2011 1 次提交
-
-
由 Junio C Hamano 提交于
This optimizes the "recency order" (see pack-heuristics.txt in Documentation/technical/ directory) used to order objects within a packfile in three ways: - Commits at the tip of tags are written together, in the hope that revision traversal done in incremental fetch (which starts by putting them in a revision queue marked as UNINTERESTING) will see a better locality of these objects; - In the original recency order, trees and blobs are intermixed. Write trees together before blobs, in the hope that this will improve locality when running pathspec-limited revision traversal, i.e. "git log paths..."; - When writing blob objects out, write the whole family of blobs that use the same delta base object together, by starting from the root of the delta chain, and writing its immediate children in a width-first manner, in the hope that this will again improve locality when reading blobs that belong to the same path, which are likely to be deltified against each other. I tried various workloads in the Linux kernel repositories (HEAD at v3.0-rc6-71-g4dd1b49) packed with v1.7.6 and with this patch, counting how large seeks are needed between adjacent accesses to objects in the pack, and the result looks promising. The history has 2072052 objects, weighing some 490MiB. * Simple commit-only log. $ git log >/dev/null There are 254656 commits in total. v1.7.6 with patch Total number of access : 258,031 258,032 0.0% percentile : 12 12 10.0% percentile : 259 259 20.0% percentile : 294 294 30.0% percentile : 326 326 40.0% percentile : 363 363 50.0% percentile : 415 415 60.0% percentile : 513 513 70.0% percentile : 857 858 80.0% percentile : 10,434 10,441 90.0% percentile : 91,985 91,996 95.0% percentile : 260,852 260,885 99.0% percentile : 1,150,680 1,152,811 99.9% percentile : 3,148,435 3,148,435 Less than 2MiB seek: 99.70% 99.69% 95% of the pack accesses look at data that is no further than 260kB from the previous location we accessed. The patch does not change the order of commit objects very much, and the result is very similar. * Pathspec-limited log. $ git log drivers/net >/dev/null The path is touched by 26551 commits and merges (among 254656 total). v1.7.6 with patch Total number of access : 559,511 558,663 0.0% percentile : 0 0 10.0% percentile : 182 167 20.0% percentile : 259 233 30.0% percentile : 357 304 40.0% percentile : 714 485 50.0% percentile : 5,046 3,976 60.0% percentile : 688,671 443,578 70.0% percentile : 319,574,732 110,370,100 80.0% percentile : 361,647,599 123,707,229 90.0% percentile : 393,195,669 128,947,636 95.0% percentile : 405,496,875 131,609,321 99.0% percentile : 412,942,470 133,078,115 99.5% percentile : 413,172,266 133,163,349 99.9% percentile : 413,354,356 133,240,445 Less than 2MiB seek: 61.71% 62.87% With the current pack heuristics, more than 30% of accesses have to seek further than 300MB; the updated pack heuristics ensures that less than 0.1% of accesses have to seek further than 135MB. This is largely due to the fact that the updated heuristics does not mix blobs and trees together. * Blame. $ git blame drivers/net/ne.c >/dev/null The path is touched by 34 commits and merges. v1.7.6 with patch Total number of access : 178,147 178,166 0.0% percentile : 0 0 10.0% percentile : 142 139 20.0% percentile : 222 194 30.0% percentile : 373 300 40.0% percentile : 1,168 837 50.0% percentile : 11,248 7,334 60.0% percentile : 305,121,284 106,850,130 70.0% percentile : 361,427,854 123,709,715 80.0% percentile : 388,127,343 128,171,047 90.0% percentile : 399,987,762 130,200,707 95.0% percentile : 408,230,673 132,174,308 99.0% percentile : 412,947,017 133,181,160 99.5% percentile : 413,312,798 133,220,425 99.9% percentile : 413,352,366 133,269,051 Less than 2MiB seek: 56.47% 56.83% The result is very similar to the pathspec-limited log above, which only looks at the tree objects. * Packing recent history. $ (git for-each-ref --format='^%(refname)' refs/tags; echo HEAD) | git pack-objects --revs --stdout >/dev/null This should pack data worth 71 commits. v1.7.6 with patch Total number of access : 11,511 11,514 0.0% percentile : 0 0 10.0% percentile : 48 47 20.0% percentile : 134 98 30.0% percentile : 332 178 40.0% percentile : 1,386 293 50.0% percentile : 8,030 478 60.0% percentile : 33,676 1,195 70.0% percentile : 147,268 26,216 80.0% percentile : 9,178,662 464,598 90.0% percentile : 67,922,665 965,782 95.0% percentile : 87,773,251 1,226,102 99.0% percentile : 98,011,763 1,932,377 99.5% percentile : 100,074,427 33,642,128 99.9% percentile : 105,336,398 275,772,650 Less than 2MiB seek: 77.09% 99.04% The long-tail part of the result looks worse with the patch, but the change helps majority of the access. 99.04% of the accesses need less than 2MiB of seeking, compared to 77.09% with the current packing heuristics. * Index pack. $ git index-pack -v .git/objects/pack/pack*.pack v1.7.6 with patch Total number of access : 2,791,228 2,788,802 0.0% percentile : 9 9 10.0% percentile : 140 89 20.0% percentile : 233 167 30.0% percentile : 322 235 40.0% percentile : 464 310 50.0% percentile : 862 423 60.0% percentile : 2,566 686 70.0% percentile : 25,827 1,498 80.0% percentile : 1,317,862 4,971 90.0% percentile : 11,926,385 119,398 95.0% percentile : 41,304,149 952,519 99.0% percentile : 227,613,070 6,709,650 99.5% percentile : 321,265,121 11,734,871 99.9% percentile : 382,919,785 33,155,191 Less than 2MiB seek: 81.73% 96.92% As the index-pack command already walks objects in the delta chain order, writing the blobs out in the delta chain order seems to drastically improve the locality of access. Note that a half-a-gigabyte packfile comfortably fits in the buffer cache, and you would unlikely to see much performance difference on a modern and reasonably beefy machine with enough memory and local disks. Benchmarking with cold cache (or over NFS) would be interesting. Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 11 6月, 2011 3 次提交
-
-
由 Junio C Hamano 提交于
The size of objects we read from the repository and data we try to put into the repository are represented in "unsigned long", so that on larger architectures we can handle objects that weigh more than 4GB. But the interface defined in zlib.h to communicate with inflate/deflate limits avail_in (how many bytes of input are we calling zlib with) and avail_out (how many bytes of output from zlib are we ready to accept) fields effectively to 4GB by defining their type to be uInt. In many places in our code, we allocate a large buffer (e.g. mmap'ing a large loose object file) and tell zlib its size by assigning the size to avail_in field of the stream, but that will truncate the high octets of the real size. The worst part of this story is that we often pass around z_stream (the state object used by zlib) to keep track of the number of used bytes in input/output buffer by inspecting these two fields, which practically limits our callchain to the same 4GB limit. Wrap z_stream in another structure git_zstream that can express avail_in and avail_out in unsigned long. For now, just die() when the caller gives a size that cannot be given to a single zlib call. In later patches in the series, we would make git_inflate() and git_deflate() internally loop to give callers an illusion that our "improved" version of zlib interface can operate on a buffer larger than 4GB in one go. Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Junio C Hamano 提交于
Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
由 Junio C Hamano 提交于
Wrap deflateInit, deflate, and deflateEnd for everybody, and the sole use of deflateInit2 in remote-curl.c to tell the library to use gzip header and trailer in git_deflate_init_gzip(). There is only one caller that cares about the status from deflateEnd(). Introduce git_deflate_end_gently() to let that sole caller retrieve the status and act on it (i.e. die) for now, but we would probably want to make inflate_end/deflate_end die when they ran out of memory and get rid of the _gently() kind. Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 06 4月, 2011 1 次提交
-
-
由 Junio C Hamano 提交于
The pack-objects command should take notice of the object file and refrain from attempting to delta large ones, to be consistent with the fast-import command. Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-
- 28 2月, 2011 1 次提交
-
-
由 Junio C Hamano 提交于
Remove two globals, pack_idx_default version and pack_idx_off32_limit, and place them in a pack_idx_option structure. Allow callers to pass it to write_idx_file() as a parameter. Adjust all callers to the API change. Signed-off-by: NJunio C Hamano <gitster@pobox.com>
-