The gitattributes machinery is being taught to work better in a
multi-threaded environment.
* bw/attr: (27 commits)
attr: reformat git_attr_set_direction() function
attr: push the bare repo check into read_attr()
attr: store attribute stack in attr_check structure
attr: tighten const correctness with git_attr and match_attr
attr: remove maybe-real, maybe-macro from git_attr
attr: eliminate global check_all_attr array
attr: use hashmap for attribute dictionary
attr: change validity check for attribute names to use positive logic
attr: pass struct attr_check to collect_some_attrs
attr: retire git_check_attrs() API
attr: convert git_check_attrs() callers to use the new API
attr: convert git_all_attrs() to use "struct attr_check"
attr: (re)introduce git_check_attr() and struct attr_check
attr: rename function and struct related to checking attributes
attr.c: outline the future plans by heavily commenting
Documentation: fix a typo
attr.c: add push_stack() helper
attr: support quoting pathname patterns in C style
attr.c: plug small leak in parse_attr_line()
attr.c: tighten constness around "git_attr" structure
...
"git repack --depth=<n>" for a long time busted the specified depth
when reusing delta from existing packs. This has been corrected.
* jk/delta-chain-limit:
pack-objects: convert recursion to iteration in break_delta_chain()
pack-objects: enforce --depth limit in reused deltas
Convert each_loose_object_fn and each_packed_object_fn to take a pointer
to struct object_id. Update the various callbacks. Convert several
40-based constants to use GIT_SHA1_HEXSZ.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The remaining callers are all simple "I have N attributes I am
interested in. I'll ask about them with various paths one by one".
After this step, no caller to git_check_attrs() remains. After
removing it, we can extend "struct attr_check" struct with data
that can be used in optimizing the query for the specific N
attributes it contains.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The traditional API to check attributes is to prepare an N-element
array of "struct git_attr_check" and pass N and the array to the
function "git_check_attr()" as arguments.
In preparation to revamp the API to pass a single structure, in
which these N elements are held, rename the type used for these
individual array elements to "struct attr_check_item" and rename
the function to "git_check_attrs()".
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The break_delta_chain() function is recursive over the depth
of a given delta chain, which can lead to possibly running
out of stack space. Normally delta depth is quite small, but
if there _is_ a pathological case, this is where we would
find and fix it, so we should be more careful.
We can do it without recursion at all, but there's a little
bit of cleverness needed to do so. It's easiest to explain
by covering the less-clever strategies first.
The obvious thing to try is just keeping our own stack on
the heap. Whenever we would recurse, push the new entry onto
the stack and loop instead. But this gets tricky; when we
see an ACTIVE entry, we need to care if we just pushed it
(in which case it's a cycle) or if we just popped it (in
which case we dealt with its bases, and no we need to clear
the ACTIVE flag and compute its depth).
You can hack around that in various ways, like keeping a
"just pushed" flag, but the logic gets muddled. However, we
can observe that we do all of our pushes first, and then all
of our pops afterwards. In other words, we can do this in
two passes. First dig down to the base, stopping when we see
a cycle, and pushing each item onto our stack. Then pop the
stack elements, clearing the ACTIVE flag and computing the
depth for each.
This works, and is reasonably elegant. However, why do we
need the stack for the second pass? We can just walk the
delta pointers again. There's one complication. Popping the
stack went over our list in reverse, so we could compute the
depth of each entry by incrementing the depth of its base,
which we will have just computed. To go forward in the
second pass, we have to compute the total depth on the way
down, and then assign it as we go.
This patch implements this final strategy, because it not
only keeps the memory off the stack, but it eliminates it
entirely. Credit for the cleverness in that approach goes to
Michael Haggerty; bugs are mine.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Since 898b14c (pack-objects: rework check_delta_limit usage,
2007-04-16), we check the delta depth limit only when
figuring out whether we should make a new delta. We don't
consider it at all when reusing deltas, which means that
packing once with --depth=250, and then again with
--depth=50, the second pack may still contain chains larger
than 50.
This is generally considered a feature, as the results of
earlier high-depth repacks are carried forward, used for
serving fetches, etc. However, since we started using
cross-pack deltas in c9af708b1 (pack-objects: use mru list
when iterating over packs, 2016-08-11), we are no longer
bounded by the length of an existing delta chain in a single
pack.
Here's one particular pathological case: a sequence of N
packs, each with 2 objects, the base of which is stored as a
delta in a previous pack. If we chain all the deltas
together, we have a cycle of length N. We break the cycle,
but the tip delta is still at depth N-1.
This is less unlikely than it might sound. See the included
test for a reconstruction based on real-world actions. I
ran into such a case in the wild, where a client was rapidly
sending packs, and we had accumulated 10,000 before doing a
server-side repack. The pack that "git repack" tried to
generate had a very deep chain, which caused pack-objects to
run out of stack space in the recursive write_one().
This patch bounds the length of delta chains in the output
pack based on --depth, regardless of whether they are caused
by cross-pack deltas or existed in the input packs. This
fixes the problem, but does have two possible downsides:
1. High-depth aggressive repacks followed by "normal"
repacks will throw away the high-depth chains.
In the long run this is probably OK; investigation
showed that high-depth repacks aren't actually
beneficial, and we dropped the aggressive depth default
to match the normal case in 07e7dbf0d (gc: default
aggressive depth to 50, 2016-08-11).
2. If you really do want to store high-depth deltas on
disk, they may be discarded and new delta computed when
serving a fetch, unless you set pack.depth to match
your high-depth size.
The implementation uses the existing search for delta
cycles. That lets us compute the depth of any node based on
the depth of its base, because we know the base is DFS_DONE
by the time we look at it (modulo any cycles in the graph,
but we know there cannot be any because we break them as we
see them).
There is some subtlety worth mentioning, though. We record
the depth of each object as we compute it. It might seem
like we could save the per-object storage space by just
keeping track of the depth of our traversal (i.e., have
break_delta_chains() report how deep it went). But we may
visit an object through multiple delta paths, and on
subsequent paths we want to know its depth immediately,
without having to walk back down to its final base (doing so
would make our graph walk quadratic rather than linear).
Likewise, one could try to record the depth not from the
base, but from our starting point (i.e., start
recursion_depth at 0, and pass "recursion_depth + 1" to each
invocation of break_delta_chains()). And then when
recursion_depth gets too big, we know that we must cut the
delta chain. But that technique is wrong if we do not visit
the nodes in topological order. In a chain A->B->C, it
if we visit "C", then "B", then "A", we will never recurse
deeper than 1 link (because we see at each node that we have
already visited it).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are three codepaths that use a variable whose name is
pack_compression_level to affect how objects and deltas sent to a
packfile is compressed. Unlike zlib_compression_level that controls
the loose object compression, however, this variable was static to
each of these codepaths. Two of them read the pack.compression
configuration variable, using core.compression as the default, and
one of them also allowed overriding it from the command line.
The other codepath in bulk-checkin did not pay any attention to the
configuration.
Unify the configuration parsing to git_default_config(), where we
implement the parsing of core.loosecompression and core.compression
and make the former override the latter, by moving code to parse
pack.compression and also allow core.compression to give default to
this variable.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This function is meant to be used when reading from files in the
object store, and the original objective was to avoid smudging atime
of loose object files too often, hence its name. Because we'll be
extending its role in the next commit to also arrange the file
descriptors they return auto-closed in the child processes, rename
it to lose "noatime" part that is too specific.
Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git pack-objects" in a repository with many packfiles used to
spend a lot of time looking for/at objects in them; the accesses to
the packfiles are now optimized by checking the most-recently-used
packfile first.
* jk/pack-objects-optim-mru:
pack-objects: use mru list when iterating over packs
pack-objects: break delta cycles before delta-search phase
sha1_file: make packed_object_info public
provide an initializer for "struct object_info"
Apply the semantic patch contrib/coccinelle/qsort.cocci to the code
base, replacing calls of qsort(3) with QSORT. The resulting code is
shorter and supports empty arrays with NULL pointers.
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Some codepaths in "git pack-objects" were not ready to use an
existing pack bitmap; now they are and as the result they have
become faster.
* ks/pack-objects-bitmap:
pack-objects: use reachability bitmap index when generating non-stdout pack
pack-objects: respect --local/--honor-pack-keep/--incremental when bitmap is in use
"git pack-objects --include-tag" was taught that when we know that
we are sending an object C, we want a tag B that directly points at
C but also a tag A that points at the tag B. We used to miss the
intermediate tag B in some cases.
* jk/pack-tag-of-tag:
pack-objects: walk tag chains for --include-tag
t5305: simplify packname handling
t5305: use "git -C"
t5305: drop "dry-run" of unpack-objects
t5305: move cleanup into test block
Starting from 6b8fda2d (pack-objects: use bitmaps when packing objects)
if a repository has bitmap index, pack-objects can nicely speedup
"Counting objects" graph traversal phase. That however was done only for
case when resultant pack is sent to stdout, not written into a file.
The reason here is for on-disk repack by default we want:
- to produce good pack (with bitmap index not-yet-packed objects are
emitted to pack in suboptimal order).
- to use more robust pack-generation codepath (avoiding possible
bugs in bitmap code and possible bitmap index corruption).
Jeff King further explains:
The reason for this split is that pack-objects tries to determine how
"careful" it should be based on whether we are packing to disk or to
stdout. Packing to disk implies "git repack", and that we will likely
delete the old packs after finishing. We want to be more careful (so
as not to carry forward a corruption, and to generate a more optimal
pack), and we presumably run less frequently and can afford extra CPU.
Whereas packing to stdout implies serving a remote via "git fetch" or
"git push". This happens more frequently (e.g., a server handling many
fetching clients), and we assume the receiving end takes more
responsibility for verifying the data.
But this isn't always the case. One might want to generate on-disk
packfiles for a specialized object transfer. Just using "--stdout" and
writing to a file is not optimal, as it will not generate the matching
pack index.
So it would be useful to have some way of overriding this heuristic:
to tell pack-objects that even though it should generate on-disk
files, it is still OK to use the reachability bitmaps to do the
traversal.
So we can teach pack-objects to use bitmap index for initial object
counting phase when generating resultant pack file too:
- if we take care to not let it be activated under git-repack:
See above about repack robustness and not forward-carrying corruption.
- if we know bitmap index generation is not enabled for resultant pack:
The current code has singleton bitmap_git, so it cannot work
simultaneously with two bitmap indices.
We also want to avoid (at least with current implementation)
generating bitmaps off of bitmaps. The reason here is: when generating
a pack, not-yet-packed objects will be emitted into pack in
suboptimal order and added to tail of the bitmap as "extended entries".
When the resultant pack + some new objects in associated repository
are in turn used to generate another pack with bitmap, the situation
repeats: new objects are again not emitted optimally and just added to
bitmap tail - not in recency order.
So the pack badness can grow over time when at each step we have
bitmapped pack + some other objects. That's why we want to avoid
generating bitmaps off of bitmaps, not to let pack badness grow.
- if we keep pack reuse enabled still only for "send-to-stdout" case:
Because pack-to-file needs to generate index for destination pack, and
currently on pack reuse raw entries are directly written out to the
destination pack by write_reused_pack(), bypassing needed for pack index
generation bookkeeping done by regular codepath in write_one() and
friends.
( In the future we might teach pack-reuse code about cases when index
also needs to be generated for resultant pack and remove
pack-reuse-only-for-stdout limitation )
This way for pack-objects -> file we get nice speedup:
erp5.git[1] (~230MB) extracted from ~ 5GB lab.nexedi.com backup
repository managed by git-backup[2] via
time echo 0186ac99 | git pack-objects --revs erp5pack
before: 37.2s
after: 26.2s
And for `git repack -adb` packed git.git
time echo 5c589a73 | git pack-objects --revs gitpack
before: 7.1s
after: 3.6s
i.e. it can be 30% - 50% speedup for pack extraction.
git-backup extracts many packs on repositories restoration. That was my
initial motivation for the patch.
[1] https://lab.nexedi.com/nexedi/erp5
[2] https://lab.nexedi.com/kirr/git-backup
NOTE
Jeff also suggests that pack.useBitmaps was probably a mistake to
introduce originally. This way we are not adding another config point,
but instead just always default to-file pack-objects not to use bitmap
index: Tools which need to generate on-disk packs with using bitmap, can
pass --use-bitmap-index explicitly. And git-repack does never pass
--use-bitmap-index, so this way we can be sure regular on-disk repacking
remains robust.
NOTE2
`git pack-objects --stdout >file.pack` + `git index-pack file.pack` is much slower
than `git pack-objects file.pack`. Extracting erp5.git pack from
lab.nexedi.com backup repository:
$ time echo 0186ac99 | git pack-objects --stdout --revs >erp5pack-stdout.pack
real 0m22.309s
user 0m21.148s
sys 0m0.932s
$ time git index-pack erp5pack-stdout.pack
real 0m50.873s <-- more than 2 times slower than time to generate pack itself!
user 0m49.300s
sys 0m1.360s
So the time for
`pack-object --stdout >file.pack` + `index-pack file.pack` is 72s,
while
`pack-objects file.pack` which does both pack and index is 27s.
And even
`pack-objects --no-use-bitmap-index file.pack` is 37s.
Jeff explains:
The packfile does not carry the sha1 of the objects. A receiving
index-pack has to compute them itself, including inflating and applying
all of the deltas.
that's why for `git-backup restore` we want to teach `git pack-objects
file.pack` to use bitmaps instead of using `git pack-objects --stdout
>file.pack` + `git index-pack file.pack`.
NOTE3
The speedup is now tracked via t/perf/p5310-pack-bitmaps.sh
Test 56dfeb62 this tree
--------------------------------------------------------------------------------
5310.2: repack to disk 8.98(8.05+0.29) 9.05(8.08+0.33) +0.8%
5310.3: simulated clone 2.02(2.27+0.09) 2.01(2.25+0.08) -0.5%
5310.4: simulated fetch 0.81(1.07+0.02) 0.81(1.05+0.04) +0.0%
5310.5: pack to file 7.58(7.04+0.28) 7.60(7.04+0.30) +0.3%
5310.6: pack to file (bitmap) 7.55(7.02+0.28) 3.25(2.82+0.18) -57.0%
5310.8: clone (partial bitmap) 1.83(2.26+0.12) 1.82(2.22+0.14) -0.5%
5310.9: pack to file (partial bitmap) 6.86(6.58+0.30) 2.87(2.74+0.20) -58.2%
More context:
http://marc.info/?t=146792101400001&r=1&w=2http://public-inbox.org/git/20160707190917.20011-1-kirr@nexedi.com/T/#t
Cc: Vicent Marti <tanoku@gmail.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Kirill Smelkov <kirr@nexedi.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Since 6b8fda2d (pack-objects: use bitmaps when packing objects) there
are two codepaths in pack-objects: with & without using bitmap
reachability index.
However add_object_entry_from_bitmap(), despite its non-bitmapped
counterpart add_object_entry(), in no way does check for whether --local
or --honor-pack-keep or --incremental should be respected. In
non-bitmapped codepath this is handled in want_object_in_pack(), but
bitmapped codepath has simply no such checking at all.
The bitmapped codepath however was allowing to pass in all those options
and with bitmap indices still being used under such conditions -
potentially giving wrong output (e.g. including objects from non-local or
.keep'ed pack).
We can easily fix this by noting the following: when an object comes to
add_object_entry_from_bitmap() it can come for two reasons:
1. entries coming from main pack covered by bitmap index, and
2. object coming from, possibly alternate, loose or other packs.
"2" can be already handled by want_object_in_pack() and to cover
"1" we can teach want_object_in_pack() to expect that *found_pack can be
non-NULL, meaning calling client already found object's pack entry.
In want_object_in_pack() we care to start the checks from already found
pack, if we have one, this way determining the answer right away
in case neither --local nor --honour-pack-keep are active. In
particular, as p5310-pack-bitmaps.sh shows (3 consecutive runs), we do
not do harm to served-with-bitmap clones performance-wise:
Test 56dfeb62 this tree
-----------------------------------------------------------------
5310.2: repack to disk 9.08(8.20+0.25) 9.09(8.14+0.32) +0.1%
5310.3: simulated clone 1.92(2.12+0.08) 1.93(2.12+0.09) +0.5%
5310.4: simulated fetch 0.82(1.07+0.04) 0.82(1.06+0.04) +0.0%
5310.6: partial bitmap 1.96(2.42+0.13) 1.95(2.40+0.15) -0.5%
Test 56dfeb62 this tree
-----------------------------------------------------------------
5310.2: repack to disk 9.11(8.16+0.32) 9.11(8.19+0.28) +0.0%
5310.3: simulated clone 1.93(2.14+0.07) 1.92(2.11+0.10) -0.5%
5310.4: simulated fetch 0.82(1.06+0.04) 0.82(1.04+0.05) +0.0%
5310.6: partial bitmap 1.95(2.38+0.16) 1.94(2.39+0.14) -0.5%
Test 56dfeb62 this tree
-----------------------------------------------------------------
5310.2: repack to disk 9.13(8.17+0.31) 9.07(8.13+0.28) -0.7%
5310.3: simulated clone 1.92(2.13+0.07) 1.91(2.12+0.06) -0.5%
5310.4: simulated fetch 0.82(1.08+0.03) 0.82(1.08+0.03) +0.0%
5310.6: partial bitmap 1.96(2.43+0.14) 1.96(2.42+0.14) +0.0%
with delta timings showing they are all within noise from run to run.
In the general case we do not want to call find_pack_entry_one() more than
once, because it is expensive. This patch splits the loop in
want_object_in_pack() into two parts: finding the object and seeing if it
impacts our choice to include it in the pack. We may call the inexpensive
want_found_object() twice, but we will never call find_pack_entry_one() if we
do not need to.
I appreciate help and discussing this change with Junio C Hamano and
Jeff King.
Signed-off-by: Kirill Smelkov <kirr@nexedi.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When pack-objects is given --include-tag, it peels each tag
ref down to a non-tag object, and if that non-tag object is
going to be packed, we include the tag, too. But what
happens if we have a chain of tags (e.g., tag "A" points to
tag "B", which points to commit "C")?
We'll peel down to "C" and realize that we want to include
tag "A", but we do not ever consider tag "B", leading to a
broken pack (assuming "B" was not otherwise selected).
Instead, we have to walk the whole chain, adding any tags we
find to the pack.
Interestingly, it doesn't seem possible to trigger this
problem with "git fetch", but you can with "git clone
--single-branch". The reason is that we generate the correct
pack when the client explicitly asks for "A" (because we do
a real reachability analysis there), and "fetch" is more
willing to do so. There are basically two cases:
1. If "C" is already a ref tip, then the client can deduce
that it needs "A" itself (via find_non_local_tags), and
will ask for it explicitly rather than relying on the
include-tag capability. Everything works.
2. If "C" is not already a ref tip, then we hope for
include-tag to send us the correct tag. But it doesn't;
it generates a broken pack. However, the next step is
to do a follow-up run of find_non_local_tags(),
followed by fetch_refs() to backfill any tags we
learned about.
In the normal case, fetch_refs() calls quickfetch(),
which does a connectivity check and sees we have no
new objects to fetch. We just write the refs.
But for the broken-pack case, the connectivity check
fails, and quickfetch will follow-up with the remote,
asking explicitly for each of the ref tips. This picks
up the missing object in a new pack.
For a regular "git clone", we are similarly OK, because we
explicitly request all of the tag refs, and get a correct
pack. But with "--single-branch", we kick in tag
auto-following via "include-tag", but do _not_ do a
follow-up backfill. We just take whatever the server sent us
via include-tag and write out tag refs for any tag objects
we were sent. So prior to c6807a4 (clone: open a shortcut
for connectivity check, 2013-05-26), we actually claimed the
clone was a success, but the result was silently
corrupted! Since c6807a4, index-pack's connectivity
check catches this case, and we correctly complain.
The included test directly checks that pack-objects does not
generate a broken pack, but also confirms that "clone
--single-branch" does not hit the bug.
Note that tag chains introduce another interesting question:
if we are packing the tag "B" but not the commit "C", should
"A" be included?
Both before and after this patch, we do not include "A",
because the initial peel_ref() check only knows about the
bottom-most level, "C". To realize that "B" is involved at
all, we would have to switch to an incremental peel, in
which we examine each tagged object, asking if it is being
packed (and including the outer tag if so).
But that runs contrary to the optimizations in peel_ref(),
which avoid accessing the objects at all, in favor of using
the value we pull from packed-refs. It's OK to walk the
whole chain once we know we're going to include the tag (we
have to access it anyway, so the effort is proportional to
the pack we're generating). But for the initial selection,
we have to look at every ref. If we're only packing a few
objects, we'd still have to parse every single referenced
tag object just to confirm that it isn't part of a tag
chain.
This could be addressed if packed-refs stored the complete
tag chain for each peeled ref (in most cases, this would be
the same cost as now, as each "chain" is only a single
link). But given the size of that project, it's out of scope
for this fix (and probably nobody cares enough anyway, as
it's such an obscure situation). This commit limits itself
to just avoiding the creation of a broken pack.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In the original implementation of want_object_in_pack(), we
always looked for the object in every pack, so the order did
not matter for performance.
As of the last few patches, however, we can now often break
out of the loop early after finding the first instance, and
avoid looking in the other packs at all. In this case, pack
order can make a big difference, because we'd like to find
the objects by looking at as few packs as possible.
This patch switches us to the same packed_git_mru list that
is now used by normal object lookups.
Here are timings for p5303 on linux.git:
Test HEAD^ HEAD
------------------------------------------------------------------------
5303.3: rev-list (1) 31.31(31.07+0.23) 31.28(31.00+0.27) -0.1%
5303.4: repack (1) 40.35(38.84+2.60) 40.53(39.31+2.32) +0.4%
5303.6: rev-list (50) 31.37(31.15+0.21) 31.41(31.16+0.24) +0.1%
5303.7: repack (50) 58.25(68.54+2.03) 47.28(57.66+1.89) -18.8%
5303.9: rev-list (1000) 31.91(31.57+0.33) 31.93(31.64+0.28) +0.1%
5303.10: repack (1000) 304.80(376.00+3.92) 87.21(159.54+2.84) -71.4%
The rev-list numbers are unchanged, which makes sense (they
are not exercising this code at all). The 50- and 1000-pack
repack cases show considerable improvement.
The single-pack repack case doesn't, of course; there's
nothing to improve. In fact, it gives us a baseline for how
fast we could possibly go. You can see that though rev-list
can approach the single-pack case even with 1000 packs,
repack doesn't. The reason is simple: the loop we are
optimizing is only part of what the repack is doing. After
the "counting" phase, we do delta compression, which is much
more expensive when there are multiple packs, because we
have fewer deltas we can reuse (you can also see that these
numbers come from a multicore machine; the CPU times are
much higher than the wall-clock times due to the delta
phase).
So the good news is that in cases with many packs, we used
to be dominated by the "counting" phase, and now we are
dominated by the delta compression (which is faster, and
which we have already parallelized).
Here are similar numbers for git.git:
Test HEAD^ HEAD
---------------------------------------------------------------------
5303.3: rev-list (1) 1.55(1.51+0.02) 1.54(1.53+0.00) -0.6%
5303.4: repack (1) 1.82(1.80+0.08) 1.82(1.78+0.09) +0.0%
5303.6: rev-list (50) 1.58(1.57+0.00) 1.58(1.56+0.01) +0.0%
5303.7: repack (50) 2.50(3.12+0.07) 2.31(2.95+0.06) -7.6%
5303.9: rev-list (1000) 2.22(2.20+0.02) 2.23(2.19+0.03) +0.5%
5303.10: repack (1000) 10.47(16.78+0.22) 7.50(13.76+0.22) -28.4%
Not as impressive in terms of percentage, but still
measurable wins. If you look at the wall-clock time
improvements in the 1000-pack case, you can see that linux
improved by roughly 10x as many seconds as git. That's
because it has roughly 10x as many objects, and we'd expect
this improvement to scale linearly with the number of
objects (since the number of packs is kept constant). It's
just that the "counting" phase is a smaller percentage of
the total time spent for a git.git repack, and hence the
percentage win is smaller.
The implementation itself is a straightforward use of the
MRU code. We only bother marking a pack as used when we know
that we are able to break early out of the loop, for two
reasons:
1. If we can't break out early, it does no good; we have
to visit each pack anyway, so we might as well avoid
even the minor overhead of managing the cache order.
2. The mru_mark() function reorders the list, which would
screw up our traversal. So it is only safe to mark when
we are about to break out of the loop. We could record
the found pack and mark it after the loop finishes, of
course, but that's more complicated and it doesn't buy
us anything due to (1).
Note that this reordering does have a potential impact on
the final pack, as we store only a single "found" pack for
each object, even if it is present in multiple packs. In
principle, any copy is acceptable, as they all refer to the
same content. But in practice, they may differ in whether
they are stored as deltas, against which base, etc. This may
have an impact on delta reuse, and even the delta search
(since we skip pairs that were already in the same pack).
It's not clear whether this change of order would hurt or
even help average cases, though. The most likely reason to
have duplicate objects is from the completion of thin packs
(e.g., you have some objects in a "base" pack, then receive
several pushes; the packs you receive may be thin on the
wire, with deltas that refer to bases outside the pack, but
we complete them with duplicate base objects when indexing
them).
In such a case the current code would always find the thin
duplicates (because we currently walk the packs in reverse
chronological order). Whereas with this patch, some of those
duplicates would be found in the base pack instead.
In my tests repacking a real-world case of linux.git with
3600 thin-pack pushes (on top of a large "base" pack), the
resulting pack was about 0.04% larger with this patch. On
the other hand, because we were more likely to hit the base
pack, there were more opportunities for delta reuse, and we
had 50,000 fewer objects to examine in the delta search.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We do not allow cycles in the delta graph of a pack (i.e., A
is a delta of B which is a delta of A) for the obvious
reason that you cannot actually access any of the objects in
such a case.
There's a last-ditch attempt to notice cycles during the
write phase, during which we issue a warning to the user and
write one of the objects out in full. However, this is
"last-ditch" for two reasons:
1. By this time, it's too late to find another delta for
the object, so the resulting pack is larger than it
otherwise could be.
2. The warning is there because this is something that
_shouldn't_ ever happen. If it does, then either:
a. a pack we are reusing deltas from had its own
cycle
b. we are reusing deltas from multiple packs, and
we found a cycle among them (i.e., A is a delta of
B in one pack, but B is a delta of A in another,
and we choose to use both deltas).
c. there is a bug in the delta-search code
So this code serves as a final check that none of these
things has happened, warns the user, and prevents us
from writing a bogus pack.
Right now, (2b) should never happen because of the static
ordering of packs in want_object_in_pack(). If two objects
have a delta relationship, then they must be in the same
pack, and therefore we will find them from that same pack.
However, a future patch would like to change that static
ordering, which will make (2b) a common occurrence. In
preparation, we should be able to handle those kinds of
cycles better. This patch does by introducing a
cycle-breaking step during the get_object_details() phase,
when we are deciding which deltas can be reused. That gives
us the chance to feed the objects into the delta search as
if the cycle did not exist.
We'll leave the detection and warning in the write_object()
phase in place, as it still serves as a check for case (2c).
This does mean we will stop warning for (2a). That case is
caused by bogus input packs, and we ideally would warn the
user about it. However, since those cycles show up after
picking reusable deltas, they look the same as (2b) to us;
our new code will break the cycles early and the last-ditch
check will never see them.
We could do analysis on any cycles that we find to
distinguish the two cases (i.e., it is a bogus pack if and
only if every delta in the cycle is in the same pack), but
we don't need to. If there is a cycle inside a pack, we'll
run into problems not only reusing the delta, but accessing
the object data at all. So when we try to dig up the actual
size of the object, we'll hit that same cycle and kick in
our usual complain-and-try-another-source code.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git pack-objects" has a few options that tell it not to pack
objects found in certain packfiles, which require it to scan .idx
files of all available packs. The codepaths involved in these
operations have been optimized for a common case of not having any
non-local pack and/or any .kept pack.
* jk/pack-objects-optim:
pack-objects: compute local/ignore_pack_keep early
pack-objects: break out of want_object loop early
find_pack_entry: replace last_found_pack with MRU cache
add generic most-recently-used list
sha1_file: drop free_pack_by_name
t/perf: add tests for many-pack scenarios
"git pack-objects" and "git index-pack" mostly operate with off_t
when talking about the offset of objects in a packfile, but there
were a handful of places that used "unsigned long" to hold that
value, leading to an unintended truncation.
* nd/pack-ofs-4gb-limit:
fsck: use streaming interface for large blobs in pack
pack-objects: do not truncate result in-pack object size on 32-bit systems
index-pack: correct "offset" type in unpack_entry_data()
index-pack: report correct bad object offsets even if they are large
index-pack: correct "len" type in unpack_data()
sha1_file.c: use type off_t* for object_info->disk_sizep
pack-objects: pass length to check_pack_crc() without truncation
In want_object_in_pack(), we can exit early from our loop if
neither "local" nor "ignore_pack_keep" are set. If they are,
however, we must examine each pack to see if it has the
object and is non-local or has a ".keep".
It's quite common for there to be no non-local or .keep
packs at all, in which case we know ahead of time that
looking further will be pointless. We can pre-compute this
by simply iterating over the list of packs ahead of time,
and dropping the flags if there are no packs that could
match.
Another similar strategy would be to modify the loop in
want_object_in_pack() to notice that we have already found
the object once, and that we are looping only to check for
"local" and "keep" attributes. If a pack has neither of
those, we can skip the call to find_pack_entry_one(), which
is the expensive part of the loop.
This has two advantages:
- it isn't all-or-nothing; we still get some improvement
when there's a small number of kept or non-local packs,
and a large number of non-kept local packs
- it eliminates any possible race where we add new
non-local or kept packs after our initial scan. In
practice, I don't think this race matters; we already
cache the packed_git information, so somebody who adds a
new pack or .keep file after we've started will not be
noticed at all, unless we happen to need to call
reprepare_packed_git() because a lookup fails.
In other words, we're already racy, and the race is not
a big deal (losing the race means we might include an
object in the pack that would not otherwise be, which is
an acceptable outcome).
However, it also has a disadvantage: we still loop over the
rest of the packs for each object to check their flags. This
is much less expensive than doing the object lookup, but
still not free. So if we wanted to implement that strategy
to cover the non-all-or-nothing cases, we could do so in
addition to this one (so you get the most speedup in the
all-or-nothing case, and the best we can do in the other
cases). But given that the all-or-nothing case is likely the
most common, it is probably not worth the trouble, and we
can revisit this later if evidence points otherwise.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When pack-objects collects the list of objects to pack
(either from stdin, or via its internal rev-list), it
filters each one through want_object_in_pack().
This function loops through each existing packfile, looking
for the object. When we find it, we mark the pack/offset
combo for later use. However, we can't just return "yes, we
want it" at that point. If --honor-pack-keep is in effect,
we must keep looking to find it in _all_ packs, to make sure
none of them has a .keep. Likewise, if --local is in effect,
we must make sure it is not present in any non-local pack.
As a result, the sum effort of these calls is effectively
O(nr_objects * nr_packs). In an ordinary repository, we have
only a handful of packs, and this doesn't make a big
difference. But in pathological cases, it can slow the
counting phase to a crawl.
This patch notices the case that we have neither "--local"
nor "--honor-pack-keep" in effect and breaks out of the loop
early, after finding the first instance. Note that our worst
case is still "objects * packs" (i.e., we might find each
object in the last pack we look in), but in practice we will
often break out early. On an "average" repo, my git.git with
8 packs, this shows a modest 2% (a few dozen milliseconds)
improvement in the counting-objects phase of "git
pack-objects --all <foo" (hackily instrumented by sticking
exit(0) right after list_objects).
But in a much more pathological case, it makes a bigger
difference. I ran the same command on a real-world example
with ~9 million objects across 1300 packs. The counting time
dropped from 413s to 45s, an improvement of about 89%.
Note that this patch won't do anything by itself for a
normal "git gc", as it uses both --honor-pack-keep and
--local.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git pack-objects" and "git index-pack" mostly operate with off_t
when talking about the offset of objects in a packfile, but there
were a handful of places that used "unsigned long" to hold that
value, leading to an unintended truncation.
* nd/pack-ofs-4gb-limit:
fsck: use streaming interface for large blobs in pack
pack-objects: do not truncate result in-pack object size on 32-bit systems
index-pack: correct "offset" type in unpack_entry_data()
index-pack: report correct bad object offsets even if they are large
index-pack: correct "len" type in unpack_data()
sha1_file.c: use type off_t* for object_info->disk_sizep
pack-objects: pass length to check_pack_crc() without truncation
A typical diff will not show what's going on and you need to see full
functions. The core code is like this, at the end of of write_one()
e->idx.offset = *offset;
size = write_object(f, e, *offset);
if (!size) {
e->idx.offset = recursing;
return WRITE_ONE_BREAK;
}
written_list[nr_written++] = &e->idx;
/* make sure off_t is sufficiently large not to wrap */
if (signed_add_overflows(*offset, size))
die("pack too large for current definition of off_t");
*offset += size;
Here we can see that the in-pack object size is returned by
write_object (or indirectly by write_reuse_object). And it's used to
calculate object offsets, which end up in the pack index file,
generated at the end.
If "size" overflows (on 32-bit sytems, unsigned long is 32-bit while
off_t can be 64-bit), we got wrong offsets and produce incorrect .idx
file, which may make it look like the .pack file is corrupted.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
On 32 bit systems with large file support, unsigned long is 32-bit
while the two offsets in the subtraction expression (pack-objects has
the exact same expression as in sha1_file.c but not shown in diff) are
in 64-bit. If an in-pack object is larger than 2^32 len/datalen is
truncated and we get a misleading "error: bad packed object CRC for
..." as a result.
Use off_t for len and datalen. check_pack_crc() already accepts this
argument as off_t and can deal with 4+ GB.
Noticed-by: Christoph Michelbach <michelbach94@gmail.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
If you use "repack -adk" currently, we will pack all objects
that are already packed into the new pack, and then drop the
old packs. However, loose unreachable objects will be left
as-is. In theory these are meant to expire eventually with
"git prune". But if you are using "repack -k", you probably
want to keep things forever and therefore do not run "git
prune" at all. Meaning those loose objects may build up over
time and end up fooling any object-count heuristics (such as
the one done by "gc --auto", though since git-gc does not
support "repack -k", this really applies to whatever custom
scripts people might have driving "repack -k").
With this patch, we instead stuff any loose unreachable
objects into the pack along with the already-packed
unreachable objects. This may seem wasteful, but it is
really no more so than using "repack -k" in the first place.
We are at a slight disadvantage, in that we have no useful
ordering for the result, or names to hand to the delta code.
However, this is again no worse than what "repack -k" is
already doing for the packed objects. The packing of these
objects doesn't matter much because they should not be
accessed frequently (unless they actually _do_ become
referenced, but then they would get moved to a different
part of the packfile during the next repack).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The code for warning_errno/die_errno has been refactored and a new
error_errno() reporting helper is introduced.
* nd/error-errno: (41 commits)
wrapper.c: use warning_errno()
vcs-svn: use error_errno()
upload-pack.c: use error_errno()
unpack-trees.c: use error_errno()
transport-helper.c: use error_errno()
sha1_file.c: use {error,die,warning}_errno()
server-info.c: use error_errno()
sequencer.c: use error_errno()
run-command.c: use error_errno()
rerere.c: use error_errno() and warning_errno()
reachable.c: use error_errno()
mailmap.c: use error_errno()
ident.c: use warning_errno()
http.c: use error_errno() and warning_errno()
grep.c: use error_errno()
gpg-interface.c: use error_errno()
fast-import.c: use error_errno()
entry.c: use error_errno()
editor.c: use error_errno()
diff-no-index.c: use error_errno()
...
It can be tempting for a server admin to want a stable set of
long-lived packs for dumb clients; but also want to enable bitmaps
to serve smart clients more quickly.
Unfortunately, such a configuration is impossible; so at least warn
users of this incompatibility since commit 21134714 (pack-objects:
turn off bitmaps when we split packs, 2014-10-16).
Tested the warning by inspecting the output of:
make -C t t5310-pack-bitmaps.sh GIT_TEST_OPTS=-v
Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Update various codepaths to avoid manually-counted malloc().
* jk/tighten-alloc: (22 commits)
ewah: convert to REALLOC_ARRAY, etc
convert ewah/bitmap code to use xmalloc
diff_populate_gitlink: use a strbuf
transport_anonymize_url: use xstrfmt
git-compat-util: drop mempcpy compat code
sequencer: simplify memory allocation of get_message
test-path-utils: fix normalize_path_copy output buffer size
fetch-pack: simplify add_sought_entry
fast-import: simplify allocation in start_packfile
write_untracked_extension: use FLEX_ALLOC helper
prepare_{git,shell}_cmd: use argv_array
use st_add and st_mult for allocation size computation
convert trivial cases to FLEX_ARRAY macros
use xmallocz to avoid size arithmetic
convert trivial cases to ALLOC_ARRAY
convert manual allocations to argv_array
argv-array: add detach function
add helpers for allocating flex-array structs
harden REALLOC_ARRAY and xcalloc against size_t overflow
tree-diff: catch integer overflow in combine_diff_path allocation
...
Each of these cases can be converted to use ALLOC_ARRAY or
REALLOC_ARRAY, which has two advantages:
1. It automatically checks the array-size multiplication
for overflow.
2. It always uses sizeof(*array) for the element-size,
so that it can never go out of sync with the declared
type of the array.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When we find a blob at "a/b/c", we currently pass this to
our show_object_fn callbacks as two components: "a/b/" and
"c". Callbacks which want the full value then call
path_name(), which concatenates the two. But this is an
inefficient interface; the path is a strbuf, and we could
simply append "c" to it temporarily, then roll back the
length, without creating a new copy.
So we could improve this by teaching the callsites of
path_name() this trick (and there are only 3). But we can
also notice that no callback actually cares about the
broken-down representation, and simply pass each callback
the full path "a/b/c" as a string. The callback code becomes
even simpler, then, as we do not have to worry about freeing
an allocated buffer, nor rolling back our modification to
the strbuf.
This is theoretically less efficient, as some callbacks
would not bother to format the final path component. But in
practice this is not measurable. Since we use the same
strbuf over and over, our work to grow it is amortized, and
we really only pay to memcpy a few bytes.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In the previous commit, we left name_path as a thin wrapper
around a strbuf. This patch drops it entirely. As a result,
every show_object_fn callback needs to be adjusted. However,
none of their code needs to be changed at all, because the
only use was to pass it to path_name(), which now handles
the bare strbuf.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Convert all instances of get_object_hash to use an appropriate reference
to the hash member of the oid member of struct object. This provides no
functional change, as it is essentially a macro substitution.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Jeff King <peff@peff.net>
struct object is one of the major data structures dealing with object
IDs. Convert it to use struct object_id instead of an unsigned char
array. Convert get_object_hash to refer to the new member as well.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Jeff King <peff@peff.net>
Convert most instances where the sha1 member of struct object is
dereferenced to use get_object_hash. Most instances that are passed to
functions that have versions taking struct object_id, such as
get_sha1_hex/get_oid_hex, or instances that can be trivially converted
to use struct object_id instead, are not converted.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Jeff King <peff@peff.net>
The unsigned long option parsing (including 'k'/'m'/'g' suffix
parsing) is more widely applicable. Add support for OPT_MAGNITUDE
to parse-options.h and change pack-objects.c use this support.
The error behavior on parse errors follows that of OPT_INTEGER. The
name of the option that failed to parse is reported with a brief
message describing the expect format for the option argument and
then the full usage message for the command invoked.
This differs from the previous behavior for OPT_ULONG used in
pack-objects for --max-pack-size and --window-memory which used to
display the value supplied in the error message and did not display
the full usage message.
Signed-off-by: Charles Bailey <cbailey32@bloomberg.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Change typedef each_ref_fn to take a "const struct object_id *oid"
parameter instead of "const unsigned char *sha1".
To aid this transition, implement an adapter that can be used to wrap
old-style functions matching the old typedef, which is now called
"each_ref_sha1_fn"), and make such functions callable via the new
interface. This requires the old function and its cb_data to be
wrapped in a "struct each_ref_fn_sha1_adapter", and that object to be
used as the cb_data for an adapter function, each_ref_fn_adapter().
This is an enormous diff, but most of it consists of simple,
mechanical changes to the sites that call any of the "for_each_ref"
family of functions. Subsequent to this change, the call sites can be
rewritten one by one to use the new interface.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When we find an object in a packfile index, we make sure we
can still open the packfile itself (or that it is already
open), as it might have been deleted by a simultaneous
repack. If we can't access the packfile, we print a warning
for the user and tell the caller that we don't have the
object (we can then look in other packfiles, or find a loose
version, before giving up).
The warning we print to the user isn't really accomplishing
anything, and it is potentially confusing to users. In the
normal case, it is complete noise; we find the object
elsewhere, and the user does not have to care that we racily
saw a packfile index that became stale. It didn't affect the
operation at all.
A possibly more interesting case is when we later can't find
the object, and report failure to the user. In this case the
warning could be considered a clue toward that ultimate
failure. But it's not really a useful clue in practice. We
wouldn't even print it consistently (since we are racing
with another process, we might not even see the .idx file,
or we might win the race and open the packfile, completing
the operation).
This patch drops the warning entirely (not only from the
fill_pack_entry site, but also from an identical use in
pack-objects). If we did find the warning interesting in the
error case, we could stuff it away and reveal it to the user
when we later die() due to the broken object. But that
complexity just isn't worth it.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Clear the git_zstream variable at the start of git_deflate_init() etc.
so that callers don't have to do that.
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When fetching into or pushing from a shallow repository, we want to
aggressively mark edges as uninteresting, since this decreases the pack
size. However, aggressively marking edges can negatively affect
performance on large non-shallow repositories with lots of refs.
Teach pack-objects a --shallow option to indicate that we're pushing
from or fetching into a shallow repository. Use
--objects-edge-aggressive only for shallow repositories and otherwise
use --objects-edge, which performs better in the general case. Update
the callers to pass the --shallow option when they are dealing with a
shallow repository.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In commit fbd4a70 (list-objects: mark more commits as edges in
mark_edges_uninteresting - 2013-08-16), we marked an increasing number
of edges uninteresting. This change, and the subsequent change to make
this conditional on --objects-edge, are used by --thin to make much
smaller packs for shallow clones.
Unfortunately, they cause a significant performance regression when
pushing non-shallow clones with lots of refs (23.322 seconds vs.
4.785 seconds with 22400 refs). Add an option to git rev-list,
--objects-edge-aggressive, that preserves this more aggressive behavior,
while leaving --objects-edge to provide more performant behavior.
Preserve the current behavior for the moment by using the aggressive
option.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
