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Our profile says we spend about 5% of the time transforming the
hex digits into the binary format used by HashsumValue, all for
comparing them against the other strings. That makes no sense
at all.
According to callgrind, this reduces the overall instruction
count from 5,3 billion to 5 billion in my example, which
roughly matches the 5%.
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This has the effect of significantly reducing actual string
comparisons, and should improve the performance of FindGrp
a bit, although it's hardly measureable (callgrind says it
uses 10% instructions less now).
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As the volatile sources are parsed last they were sorted behind the
dpkg/status file and hence are treated as a downgrade, which isn't
really what you want to happen as from a user POV its an upgrade.
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If an iterator or a stringview has multiple dynamic objects
registered with it, it may be remapped twice. Prevent that
by noting which iterators/views we have seen and not remapping
one if we have already seen it.
We most likely do not have any instance of multiple dynamics
on a single object, but let's play safe - the overhead is not
high.
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It is a bit academic to support values which aren't big enough to fit even
the hashtables without resizing, but cleaning up ensures that we do the
right thing (aka not segfaulting) even if something goes wrong in these
deep layers. You still can't have very very small values through…
Git-Dch: Ignore
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Part of hidden classes, so conversion is abi-free.
Git-Dch: Ignore
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build-dep was implemented by parsing the build-dependencies of a package
and figuring out which packages to install/remove based on this. That
means that for the first level of dependencies build-dep was
implementing its very own resolver with all the benefits (aka: bugs)
this gives us for not using the existing resolver for all levels.
Making this work involves generating a dummy binary package with fitting
Depends and Conflicts and as we can't create them out of thin air the
cache generation needs to be involved so we end up writing a Packages
file which we want to parse – after we have parsed the other Packages
files already. With .dsc/.deb files we could add them before we started
parsing anything.
With a bit of care we can avoid generating too much data we have to
throw away again (as many parts assume that e.g. the count of packages
doesn't change midair), so that on a speed front there shouldn't be
much of a difference, but output can be slightly confusing as if we have
a completely valid cache on disk the "Reading package lists... Done" is
printed two times – but apt is pretty quick about it in that case.
Closes: #137560, #444930, #489911, #583914, #728317, #812173
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Proper debian packages do not contain ':' in the package name, so for
real packages this is a non-issue, but apt itself frequently makes use
of packages with such an illegal name for internal proposes.
Git-Dch: Ignore
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To resolve dependencies like "pkg:arch" we create a package with the
name "pkg:arch" and the architecture "any". We create these packages
only if a dependency needs it as these kind of dependencies aren't that
common. This commit ensured that in the even this architecture specific
dependency is the only relation this package has we still create the
underlying package to have them available in provides resolution.
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I only looked at parameters in the previous commit, which was
not enough: One place also generated local string views. In this
case, we only need to make ArchA dynamic, as NameA is not used
after the FindPkg() call.
Gbp-Dch: ignore
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It turns out that StringViews might need to be remapped in some
places because they come from the cache. For example, some sites
pass a Ver.VerStr() to NewProvides().
Such a StringView would become invalid during the duration of
the call if the cache is remapped, causing the program to die
with a segmentation fault.
We can take care of those issues by remapping string views in
the same way we remap all the iterators. String views are only
remapped if they point into the cache though, this allows us
to write more generic code on the callee site without having
to check whether the view points into the cache or not.
That's not as efficient as possible, but the overhead does not
appear to be measurable.
Closes: #812251
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This allows us to check if a value to be remapped was inside
the cache or not, which will become useful at a later point.
Gbp-Dch: ignore
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Architectures for packages which do not belong to the native nor a
foreign architecture (dubbed barbarian for now) which are marked
M-A:foreign still provide in their own architecture even if not for
others. Also, other M-A:foreign (and allowed) packages provide in these
barbarian architectures.
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By storing the size of the string in the cache, we can make use of
it when comparing the names in the hashtable in pkgCache::FindGrp.
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It makes no sense to check if the value is empty, as it cannot
be. It will always be a hexstring of exactly 32 bytes.
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Instead of storing a string -> map_stringitem_t mapping, create
our own data type that can point to either a normal string or
a string inside the cache.
This avoids the creation of any string and improves performance
slightly (about 4%).
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This improves performance, as we now can ignore unequal strings
based on their length already.
Gbp-Dch: ignore
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This removes some minor overhead.
Gbp-Dch: ignore
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Moving the string is likely faster than copying it. We could probably
avoid strings alltogether in the future using some more crazy code,
but I have not looked at that yet.
Gbp-Dch: ignore
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This improves performance of the cache generation on my
ARM platform (4x Cortex A15) by about 10% to 20% from
2.35-2.50 to 2.1 seconds.
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Integrity is taken care of by the checksum now.
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If we already have opened a cache, there is no point in having
to open it again.
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std::unordered_map is faster than std::map in our use case,
reducing cache generation time by about 10% in my benchmark.
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Git-Dch: Ignore
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Out of memory and similar circumstanzas could cause MMap::Map to fail
and especially the mmap/malloc calls in it. With some additional
checking we can avoid segfaults and similar in such situations – at
least in theory as if this is a real out of memory everything we do to
handle the error could just as well run into a memory problem as well…
But at least in theory (if MMap::Map is made to fail always) we can deal
with it so good that a user actually never sees a failure (as the cache
it tries to load with it fails and is discarded, so that DynamicMMap
takes over and a new one is build) instead of segfaulting.
Closes: 803417
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Reported-By: cppcheck
Git-Dch: Ignore
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Reported-By: Konomi on IRC
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Our error reporting is historically grown into some kind of mess.
A while ago I implemented stacking for the global error which is used in
this commit now to wrap calls to functions which do not report (all)
errors via return, so that only failures in those calls cause a failure
to propergate down the chain rather than failing if anything
(potentially totally unrelated) has failed at some point in the past.
This way we can avoid stopping the entire acquire process just because a
single source produced an error for example. It also means that after
the acquire process the cache is generated – even if the acquire
process had failures – as we still have the old good data around we can and
should generate a cache for (again).
There are probably more instances of this hiding, but all these looked
like the easiest to work with and fix with reasonable (aka net-positive)
effects.
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How the Multi-Arch field and pkg:<arch> dependencies interact was
discussed at DebConf15 in the "MultiArch BoF". dpkg and apt (among other
tools like dose) had a different interpretation in certain scenarios
which we resolved by agreeing on dpkg view – and this commit realizes
this agreement in code.
As was the case so far libapt sticks to the idea of trying to hide
MultiArch as much as possible from individual frontends and instead
translates it to good old SingleArch. There are certainly situations
which can be improved in frontends if they know that MultiArch is upon
them, but these are improvements – not necessary changes needed
to unbreak a frontend.
The implementation idea is simple: If we parse a dependency on foo:amd64
the dependency is formed on a package 'foo:amd64' of arch 'any'. This
package is provided by package 'foo' of arch 'amd64', but not by 'foo'
of arch 'i386'. Both of those foo packages provide each other through
(assuming foo is M-A:foreign) to allow a dependency on 'foo' to be
satisfied by either foo of amd64 or i386. Packages can also declare to
provide 'foo:amd64' which is translated to providing 'foo:amd64:any' as
well.
This indirection over provides was chosen as the alternative would be to
teach dependency resolvers how to deal with architecture specific
dependencies – which violates the design idea of avoiding resolver
changes, especially as architecture-specific dependencies are a
cornercase with quite a few subtil rules. Handling it all over versioned
provides as we already did for M-A in general seems much simpler as it
just works for them.
This switch to :any has actually a "surprising" benefit as well: Even
frontends showing a package name via .Name() [which doesn't show the
architecture] will display the "architecture" for dependencies in which
it was explicitely requested, while we will not show the 'strange' :any
arch in FullName(true) [= pretty-print] either. Before you had to
specialcase these and by default you wouldn't get these details shown.
The only identifiable disadvantage is that this complicates error
reporting and handling. apt-get's ShowBroken has existing problems with
virtual packages [it just shows the name without any reason], so that
has to be worked on eventually. The other case is that detecting if a
package is completely unknown or if it was at least referenced somewhere
needs to acount for this "split" – not that it makes a practical
difference which error is shown… but its one of the improvements
possible.
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The parameter name suggests that it should forbid the building of the
entire cache in memory, but this isn't how it was previously and as
AllowMem is false by default it actually prevents previous usecases from
working like being root and configuring apt to build no caches at all.
This should be fixed at some point to actually work, but that is hard to
pull off as it means switching the default and some callers (including
apt itself) actually did call it explicitly with false in certain
cases for no apparent reason (at least now where it is common to have
enough memory to throw at every problem and even if not is a slow apt
usally better than an apt erroring out).
Closes: 796459
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After fixing Bug#796999, we noticed that there were
some more instances of iterators which had no associated
Dynamic object, causing them to not be updated when
the cache was remapped.
This happened in two places: In NewPackage() and in
NewProvidesAllArch().
Gbp-Dch: ignore
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In both the Ver and Dep variables, we need to account for remapping,
as otherwise we would still reference the old bug.
Reproduction environment:
* An i386 system with amd64 foreign architecture
* A sources.list with
deb http://snapshot.debian.org/archive/debian/20150826T102846Z/ unstable main
deb http://snapshot.debian.org/archive/debian/20150826T102846Z/ experimental main
Thanks: Jakub Wilk for the bug report and the backtraces
Closes: #796999
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More standardization
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Switch to std::unique_ptr, as this is safer than SPtr.
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We archieve the same without the special handling now, so drop this code.
Makes supporting this abdomination a little longer bearable as well.
Git-Dch: Ignore
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The code was never active in production, it just sits there collecting
dust and given that it is never tested probably doesn't even work
anymore the way it was supposed to be (whatever that was exactly in the
first place). So just remove it before I have to "fix" it again next
time.
Git-Dch: Ignore
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Trade deduplication of code for a bunch of new virtuals, so it is
actually visible how the different indexes behave cleaning up the
interface at large in the process.
Git-Dch: Ignore
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Sources are usually defined in sources.list (and co) and are pretty
stable, but once in a while a frontend might want to add an additional
"source" like a local .deb file to install this package (No support for
'real' sources being added this way as this is a multistep process).
We had a hack in place to allow apt-get and apt to pull this of for a
short while now, but other frontends are either left in the cold by this
and/or the code for it looks dirty with FIXMEs plastering it and has on
top of this also some problems (like including these 'volatile' sources
in the srcpkgcache.bin file).
So the biggest part in this commit is actually the rewrite of the cache
generation as it is now potentially a three step process. The biggest
problem with adding support now through is that this makes a bunch of
previously mostly unusable by externs and therefore hidden classes
public, so a bit of further tuneing on this now public API is in order…
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Now that we deal with provides in a more dynamic fashion the last
remaining problem is explicit dependencies like 'Conflicts: foo' which
have to apply to all architectures, but creating them all at the same
time requires us to know all architectures ending up in the cache which
isn't needed to be the same set as all foreign architectures.
The effect is visible already now through as this prevents the creation
of a bunch of virtual packages for arch:all packages and as such also
many dependencies, just not very visible if you don't look at the stats…
Git-Dch Ignore
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Expecting the worst is easy to code, but has its disadvantages e.g.
by creating package structures which otherwise would have never
existed. By creating the provides instead at the time a package
structure is added we are well prepared for the introduction of partial
architectures, massive amounts of M-A:foreign (and :allowed) and co as
far as provides are concerned at least. We have something relatively
similar for dependencies already.
Many tests are added for both M-A states and the code cleaned to
properly support implicit provides for foreign architectures and
architectures we 'just' happen to parse.
Git-Dch: Ignore
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Before MultiArch implicits weren't a thing, so they were hidden by
default by definition. Adding them for MultiArch solved many problems,
but having no reliable way of detecting which dependency (and provides)
is implicit or not causes problems everytime we want to output
dependencies without confusing our observers with unneeded
implementation details.
The really notworthy point here is actually that we keep now a better
record of how a dependency came to be so that we can later reason about
it more easily, but that is hidden so deep down in the library internals
that change is more the problems it solves than the change itself.
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Cache generation needs a way of quickly iterating over the unique potion
of the dependencies to be able to share them. By linking them together
we can reduce the speed penality (~ 80%) with only a small reduction in
saved size (~ 20%).
Git-Dch: Ignore
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Having dependency data separated from the link between version/package
and the dependency allows use to work on sharing the depdency data a bit
as it turns out that many dependencies are in fact duplicates. How many
are duplicates various heavily with the sources configured, but for a
single Debian release the ballpark is 2 duplicates for each dependency
already (e.g. libc6 counts 18410 dependencies, but only 45 unique). Add
more releases and the duplicates count only rises to get ~6 for 3
releases. For each architecture a user has configured which given the
shear number of dependencies amounts to MBs of duplication.
We can cut down on this number, but pay a heavy price for it: In my
many releases(3) + architectures(3) test we have a 10% (~ 0.5 sec)
increase in cache creationtime, but also 10% less cachesize (~ 10 MB).
Further work is needed to rip the whole benefits from this through, so
this is just the start.
Git-Dch: Ignore
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