The MRU cache that keeps track of recently used packs is represented
using two global variables:
struct mru packed_git_mru_storage;
struct mru *packed_git_mru = &packed_git_mru_storage;
Callers never assign to the packed_git_mru pointer, though, so we can
simplify by eliminating it and using &packed_git_mru_storage (renamed
to &packed_git_mru) directly. This variable is only used by the
packfile subsystem, making this a relatively uninvasive change (and
any new unadapted callers would trigger a compile error).
Noticed while moving these globals to the object_store struct.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
alloc_packed_git() in packfile.c is duplicated from sha1_file.c. In a
subsequent commit, alloc_packed_git() will be removed from sha1_file.c.
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When checking the conditional of "while (me->remaining)", we did not
hold the lock. Calling find_deltas would still be safe, since it checks
"remaining" (after taking the lock) and is able to handle all values. In
fact, this could (currently) not trigger any bug: a bug could happen if
`remaining` transitioning from zero to non-zero races with the evaluation
of the while-condition, but these are always separated by the
data_ready-mechanism.
Make sure we have the lock when we read `remaining`. This does mean we
release it just so that find_deltas can take it immediately again. We
could tweak the contract so that the lock should be taken before calling
find_deltas, but let's defer that until someone can actually show that
"unlock+lock" has a measurable negative impact.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
If done_pbase_paths is NULL then done_pbase_paths_num must be zero and
done_pbase_path_pos() returns -1 without accessing the array, so the
check is not necessary.
If the invariant was violated then the check would make sure we keep
on going and allocate the necessary amount of memory in the next
ALLOC_GROW call. That sounds nice, but all array entries except for
one would contain garbage data.
If the invariant was violated without the check we'd get a segfault in
done_pbase_path_pos(), i.e. an observable crash, alerting us of the
presence of a bug.
Currently there is no such bug: Only the functions check_pbase_path()
and cleanup_preferred_base() change pointer and counter, and both make
sure to keep them in sync. Get rid of the check anyway to allow us to
see if later changes introduce such a defect, and to simplify the code.
Detected by Coverity Scan.
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Simplify the code for moving members inside of an array and make it more
robust by using the helper macro MOVE_ARRAY. It calculates the size
based on the specified number of elements for us and supports NULL
pointers when that number is zero. Raw memmove(3) calls with NULL can
cause the compiler to (over-eagerly) optimize out later NULL checks.
This patch was generated with contrib/coccinelle/array.cocci and spatch
(Coccinelle).
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A common pattern to free a piece of memory and assign NULL to the
pointer that used to point at it has been replaced with a new
FREE_AND_NULL() macro.
* ab/free-and-null:
*.[ch] refactoring: make use of the FREE_AND_NULL() macro
coccinelle: make use of the "expression" FREE_AND_NULL() rule
coccinelle: add a rule to make "expression" code use FREE_AND_NULL()
coccinelle: make use of the "type" FREE_AND_NULL() rule
coccinelle: add a rule to make "type" code use FREE_AND_NULL()
git-compat-util: add a FREE_AND_NULL() wrapper around free(ptr); ptr = NULL
Fix configuration codepath to pay proper attention to commondir
that is used in multi-worktree situation, and isolate config API
into its own header file.
* bw/config-h:
config: don't implicitly use gitdir or commondir
config: respect commondir
setup: teach discover_git_directory to respect the commondir
config: don't include config.h by default
config: remove git_config_iter
config: create config.h
Apply the result of the just-added coccinelle rule. This manually
excludes a few occurrences, mostly things that resulted in many
FREE_AND_NULL() on one line, that'll be manually fixed in a subsequent
change.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Stop including config.h by default in cache.h. Instead only include
config.h in those files which require use of the config system.
Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"pack-objects" can stream a slice of an existing packfile out when
the pack bitmap can tell that the reachable objects are all needed
in the output, without inspecting individual objects. This
strategy however would not work well when "--local" and other
options are in use, and need to be disabled.
* jk/disable-pack-reuse-when-broken:
t5310: fix "; do" style
pack-objects: disable pack reuse for object-selection options
The internal implementation of "git grep" has seen some clean-up.
* ab/grep-preparatory-cleanup: (31 commits)
grep: assert that threading is enabled when calling grep_{lock,unlock}
grep: given --threads with NO_PTHREADS=YesPlease, warn
pack-objects: fix buggy warning about threads
pack-objects & index-pack: add test for --threads warning
test-lib: add a PTHREADS prerequisite
grep: move is_fixed() earlier to avoid forward declaration
grep: change internal *pcre* variable & function names to be *pcre1*
grep: change the internal PCRE macro names to be PCRE1
grep: factor test for \0 in grep patterns into a function
grep: remove redundant regflags assignments
grep: catch a missing enum in switch statement
perf: add a comparison test of log --grep regex engines with -F
perf: add a comparison test of log --grep regex engines
perf: add a comparison test of grep regex engines with -F
perf: add a comparison test of grep regex engines
perf: emit progress output when unpacking & building
perf: add a GIT_PERF_MAKE_COMMAND for when *_MAKE_OPTS won't do
grep: add tests to fix blind spots with \0 patterns
grep: prepare for testing binary regexes containing rx metacharacters
grep: add a test helper function for less verbose -f \0 tests
...
"pack-objects" can stream a slice of an existing packfile out when
the pack bitmap can tell that the reachable objects are all needed
in the output, without inspecting individual objects. This
strategy however would not work well when "--local" and other
options are in use, and need to be disabled.
* jk/disable-pack-reuse-when-broken:
t5310: fix "; do" style
pack-objects: disable pack reuse for object-selection options
Conversion from uchar[20] to struct object_id continues.
* bc/object-id: (53 commits)
object: convert parse_object* to take struct object_id
tree: convert parse_tree_indirect to struct object_id
sequencer: convert do_recursive_merge to struct object_id
diff-lib: convert do_diff_cache to struct object_id
builtin/ls-tree: convert to struct object_id
merge: convert checkout_fast_forward to struct object_id
sequencer: convert fast_forward_to to struct object_id
builtin/ls-files: convert overlay_tree_on_cache to object_id
builtin/read-tree: convert to struct object_id
sha1_name: convert internals of peel_onion to object_id
upload-pack: convert remaining parse_object callers to object_id
revision: convert remaining parse_object callers to object_id
revision: rename add_pending_sha1 to add_pending_oid
http-push: convert process_ls_object and descendants to object_id
refs/files-backend: convert many internals to struct object_id
refs: convert struct ref_update to use struct object_id
ref-filter: convert some static functions to struct object_id
Convert struct ref_array_item to struct object_id
Convert the verify_pack callback to struct object_id
Convert lookup_tag to struct object_id
...
Fix a buggy warning about threads under NO_PTHREADS=YesPlease. Due to
re-using the delta_search_threads variable for both the state of the
"pack.threads" config & the --threads option, setting "pack.threads"
but not supplying --threads would trigger the warning for both
"pack.threads" & --threads.
Solve this bug by resetting the delta_search_threads variable in
git_pack_config(), it might then be set by --threads again and be
subsequently warned about, as the test I'm changing here asserts.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
If certain options like --honor-pack-keep, --local, or
--incremental are used with pack-objects, then we need to
feed each potential object to want_object_in_pack() to see
if it should be filtered out. But when the bitmap
reuse_packfile optimization is in effect, we do not call
that function at all, and in fact skip adding the objects to
the to_pack list entirely. This means we have a bug: for
certain requests we will silently ignore those options and
include objects in that pack that should not be there.
The problem has been present since the inception of the
pack-reuse code in 6b8fda2db (pack-objects: use bitmaps when
packing objects, 2013-12-21), but it was unlikely to come up
in practice. These options are generally used for on-disk
packing, not transfer packs (which go to stdout), but we've
never allowed pack reuse for non-stdout packs (until
645c432d6, we did not even use bitmaps, which the reuse
optimization relies on; after that, we explicitly turned it
off when not packing to stdout).
We can fix this by just disabling the reuse_packfile
optimization when the options are in use. In theory we could
teach the pack-reuse code to satisfy these checks, but it's
not worth the complexity. The purpose of the optimization is
to keep the amount of per-object work we do to a minimum.
But these options inherently require us to search for other
copies of each object, drowning out any benefit of the
pack-reuse optimization. But note that the optimizations
from 56dfeb626 (pack-objects: compute local/ignore_pack_keep
early, 2016-07-29) happen before pack-reuse, meaning that
specifying "--honor-pack-keep" in a repository with no .keep
files can still follow the fast path.
There are tests in t5310 that check these options with
bitmaps and --stdout, but they didn't catch the bug, and
it's hard to adapt them to do so.
One problem is that they don't use --delta-base-offset;
without that option, we always disable the reuse
optimization entirely. It would be fine to add it in (it
actually makes the test more realistic), but that still
isn't quite enough.
The other problem is that the reuse code is very picky; it
only kicks in when it can reuse most of a pack, starting
from the first byte. So we'd have to start from a fully
repacked and bitmapped state to trigger it. But the tests
for these options use a much more subtle state; they want to
be sure that the want_object_in_pack() code is allowing some
objects but not others. Doing a full repack runs counter to
that.
So this patch adds new tests at the end of the script which
create the fully-packed state and make sure that each option
is not fooled by reusable pack.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Convert lookup_tag to take a pointer to struct object_id.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Convert struct pack_idx_entry to use struct object_id by changing the
definition and applying the following semantic patch, plus the standard
object_id transforms:
@@
struct pack_idx_entry E1;
@@
- E1.sha1
+ E1.oid.hash
@@
struct pack_idx_entry *E1;
@@
- E1->sha1
+ E1->oid.hash
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Convert register_shallow and unregister_shallow to take struct
object_id. register_shallow is a caller of lookup_commit, which we will
convert later. It doesn't make sense for the registration and
unregistration functions to have incompatible interfaces, so convert
them both.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git's source code assumes that unsigned long is at least as precise as
time_t. Which is incorrect, and causes a lot of problems, in particular
where unsigned long is only 32-bit (notably on Windows, even in 64-bit
versions).
So let's just use a more appropriate data type instead. In preparation
for this, we introduce the new `timestamp_t` data type.
By necessity, this is a very, very large patch, as it has to replace all
timestamps' data type in one go.
As we will use a data type that is not necessarily identical to `time_t`,
we need to be very careful to use `time_t` whenever we interact with the
system functions, and `timestamp_t` everywhere else.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Conversion from unsigned char [40] to struct object_id continues.
* bc/object-id:
Documentation: update and rename api-sha1-array.txt
Rename sha1_array to oid_array
Convert sha1_array_for_each_unique and for_each_abbrev to object_id
Convert sha1_array_lookup to take struct object_id
Convert remaining callers of sha1_array_lookup to object_id
Make sha1_array_append take a struct object_id *
sha1-array: convert internal storage for struct sha1_array to object_id
builtin/pull: convert to struct object_id
submodule: convert check_for_new_submodule_commits to object_id
sha1_name: convert disambiguate_hint_fn to take object_id
sha1_name: convert struct disambiguate_state to object_id
test-sha1-array: convert most code to struct object_id
parse-options-cb: convert sha1_array_append caller to struct object_id
fsck: convert init_skiplist to struct object_id
builtin/receive-pack: convert portions to struct object_id
builtin/pull: convert portions to struct object_id
builtin/diff: convert to struct object_id
Convert GIT_SHA1_RAWSZ used for allocation to GIT_MAX_RAWSZ
Convert GIT_SHA1_HEXSZ used for allocation to GIT_MAX_HEXSZ
Define new hash-size constants for allocating memory
Since this structure handles an array of object IDs, rename it to struct
oid_array. Also rename the accessor functions and the initialization
constant.
This commit was produced mechanically by providing non-Documentation
files to the following Perl one-liners:
perl -pi -E 's/struct sha1_array/struct oid_array/g'
perl -pi -E 's/\bsha1_array_/oid_array_/g'
perl -pi -E 's/SHA1_ARRAY_INIT/OID_ARRAY_INIT/g'
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Convert this function by changing the declaration and definition and
applying the following semantic patch to update the callers:
@@
expression E1, E2;
@@
- sha1_array_lookup(E1, E2.hash)
+ sha1_array_lookup(E1, &E2)
@@
expression E1, E2;
@@
- sha1_array_lookup(E1, E2->hash)
+ sha1_array_lookup(E1, E2)
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are a very small number of callers which don't already use struct
object_id. Convert them.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Convert the callers to pass struct object_id by changing the function
declaration and definition and applying the following semantic patch:
@@
expression E1, E2;
@@
- sha1_array_append(E1, E2.hash)
+ sha1_array_append(E1, &E2)
@@
expression E1, E2;
@@
- sha1_array_append(E1, E2->hash)
+ sha1_array_append(E1, E2)
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Code clean-up.
* jk/fast-import-cleanup:
pack.h: define largest possible encoded object size
encode_in_pack_object_header: respect output buffer length
fast-import: use xsnprintf for formatting headers
fast-import: use xsnprintf for writing sha1s
Several callers use fixed buffers for storing the pack
object header, and they've picked 10 as a magic number. This
is reasonable, since it handles objects up to 2^67. But
let's give them a constant so it's clear that the number
isn't pulled out of thin air.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The encode_in_pack_object_header() writes a variable-length
header to an output buffer, but it doesn't actually know
long the buffer is. At first glance, this looks like it
might be possible to overflow.
In practice, this is probably impossible. The smallest
buffer we use is 10 bytes, which would hold the header for
an object up to 2^67 bytes. Obviously we're not likely to
see such an object, but we might worry that an object could
lie about its size (causing us to overflow before we realize
it does not actually have that many bytes). But the argument
is passed as a uintmax_t. Even on systems that have __int128
available, uintmax_t is typically restricted to 64-bit by
the ABI.
So it's unlikely that a system exists where this could be
exploited. Still, it's easy enough to use a normal out/len
pair and make sure we don't write too far. That protects the
hypothetical 128-bit system, makes it harder for callers to
accidentally specify a too-small buffer, and makes the
resulting code easier to audit.
Note that the one caller in fast-import tried to catch such
a case, but did so _after_ the call (at which point we'd
have already overflowed!). This check can now go away.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
